Do you need to generate absolute URLs within your MVC application?

Often this will be in the form of URLs used outside of the web-browser such as those used within Atom Publishing Protocol collections or maybe links that are going to be sent out in emails. Basically, anything where the regular relative URL won’t do.

A quick search of Google will turn up a number of blog posts or forum answers showing how to do this by creating extension methods for the Url helper class but really, everything that is needed is already baked into the MVC framework already … and I’ve only just realized it after using it since the CTP releases!

All you need to do is specify the protocol within the Url.Action or Url.RouteUrl method. Here are some regular looking URLs:

<%= Url.Action("About", "Home") %><br />
<%= Url.RouteUrl("Default", new { Action = "About" }) %><br /> 

Which produce the same output:

/Home/About
/Home/About

If we add the protocol then it changes to:

<%= Url.Action("About", "Home", null, "http") %><br />
<%= Url.RouteUrl("Default", new { Action = "About" }, "http") %><br /> 

http://localhost:51868/Home/About
http://localhost:51868/Home/About

Instead of having the ‘http’ hard-coded like that you can instead use whatever protocol was used for the request so URLs will be correct whether they are using http or https (assuming they don’t need to be a specific one), e.g.:

<%= Url.Action("About", "Home", null, Request.Url.Scheme) %><br />
<%= Url.RouteUrl("Default", new { Action = "About" }, Request.Url.Scheme) %><br />

If you just pass the protocol / scheme then the host name and port number are generated automatically based on the site that the app is running on. You can also pass the host name as well if you want (if the public host name doesn’t match the one the site is actually running on).

This works for the Url helper only, the protocol isn’t an option in the Html helper used to general complete html anchor links but I’m guessing that if you need an absolute URL you are needing something else beyond a plain link anyway and it isn’t too much trouble to just define the anchor element in a view and use the Url helper in the href attribute only.

At first glance, RenderAction and RenderPartial both do a very similar thing – they load ‘some other content’ into the view being rendered at the place they are called. Personally, I think they should be used for different scenarios so these are my thoughts on where each one should be used and why.

First though, a quick recap on what they do:

• RenderPartial renders a control with some model passed to it.
• RenderAction (or RenderSubAction which addresses some issues) calls a controller action and then renders whatever view that returns with whatever model that controller action passes through it.

Hmmn, they sound pretty similar don’t they! The thing to note though is that the model passed to RenderPartial is either the current model being rendered by the calling view or a subset of it. Anything that a RenderPartial view being called is going to need has to be passed into the Model of the calling view. The view rendered using RenderAction on the other hand could contain a completely different model with no need for this to be passed in to our parent view.

Because of this, I think RenderPartial is most appropriate when what it is going to output could be considered part of the calling view but separating it out into a user control makes sense to allow re-use and avoid repeating the same rendering code in multiple views. For example, if you are rendering a person name in lots of places then instead of repeating within each view the code to output it:

<a href="<%= Url.Action("Display", "Person", new { id = Model.Person.Id}) %>">
  <%= Model.Person.Salutation %> <%= Model.Person.Forename %> <%= Model.Person.Surname %>
</a>

Instead, you move this to a separate user control such as ‘PersonName.ascx’ which expects a Person as the model:

<%@ Control Language="C#" Inherits="System.Web.Mvc.ViewUserControl<Person>" %>
<a href="<%= Url.Action("Display", "Person", new { id = Model.Id}) %>">
    <%= Model.Salutation %> <%= Model.Forename %> <%= Model.Surname %>
</a>

Now, any place a view wants to output a persons name then you can instead call a PartialView and pass in the appropriate model:

<%= Html.RenderPartial("PersonName", Model.Person); %> 

Why would you want to do this? Well, it helps consistency and avoids repetition which makes it easy if, for example, you decide that name should not longer be in the format “Mr John Smith” but instead “Smith, John (Mr)” and you want to throw in a little jQuery magic to display a profile popup whenever anyone hovers the mouse over the name. This is a simple example but hopefully it demonstrates some benefits of using it compared to repeating the code in each view – with larger chunks of output the benefits of using RenderPartial would be even more apparent

So that is where and how I think RenderPartial should be used. How about RenderAction?

Well, I think this has it’s place when the thing that needs to be rendered isn’t the responsibility of the calling view or controller.

For example, I may have a PersonController responsible for CRUD operations on the Person class including a Display action and view but I do not want either of these to have any responsibility for anything to do with the display of Projects that the person is working on. If I want to display a list of assigned projects within the Person Display view then I would use RenderAction to add it but the responsibility and knowledge of how to do this resides with the ProjectController and it’s views. This would be called as follows:

<% Html.RenderAction("List", "Project", new {personId = Model.Person.Id}); %> 

(incidentally … note that, unlike many of the other extension methods, RenderAction doesn’t return a string so there is no ‘=’ at the beginning and a ‘;’ at the end)

Now, how the Project List is retrieved and rendered is completely the concern of the ProjectController class as it should be and the output can contain whatever it needs to display the list, provide actions to edit project entries and so on.

Another benefit of this approach is if you create different skinned versions of an app. By keeping things modular it is much easier to decide to include something in the view for one skin but not another. So, the skin (set of views) for a full desktop browser may call RenderAction to include the list in the same page whereas the skin for a mobile device friendly interface (think iPhone) would perhaps just include a link instead – both are handled by changing the view instead of changing the controllers which could otherwise be the case.

The ASP.NET MVC Futures assembly contains several RenderAction extension methods for HtmlHelper to allow another action to be rendered at some point within a view. Typically, this allows each controller to handle different responsibilities rather than things being combined into the parent.

So, for example, a PersonController is responsible for retrieving and assembling the model to represent a Person and pass it to the View for rendering but it should not handle Contacts – the display and CRUD operations on contacts should be handled by a ContactController and RenderAction is a convenient way to insert a list of contacts for a person into the persion display view.

So, we have a PersonController which will retrieve a Person model and pass it to the Display view. Inside this Display view, we have a call to render a list of contacts for that person:

<% Html.RenderSubAction("List", "Contact", new { personId = Model.Id }); %>

I’ve come across two problems when using this though:

1. If the parent controller action requested uses the HTTP POST method then the controller action picked up for all child actions will also be the POST version (if there is one). This is rarely the desired behavior though – I’d only expect to be sending a POST to the ContactController when I want to change something related to a contact and not when updating a person.

2. If the [ValidateInput(false)] attribute is used to allow HTML code to be posted (imagine a ‘Biography’ field on Person with a nice WYSIWYG TinyMCE Editor control …) then the request will fail unless all the child actions are automatically marked with the same attribute. I would prefer to only have to mark the methods I specifically want a POST request containing HTML input to be called.

So, I created a set of alternative RenderSubAction extension methods which address both these issues:

1. Whatever the HTTP method used for the parent action, the routing will match the GET version for child actions called.

2. The state of the [ValidateInput()] attribute will be set on all child actions called.

The code is below … just reference the namespace that you put it in within your web.config file and then change the RenderAction method to RenderSubAction – the method signatures are identical so it is a drop-in replacement.

I’d be interested in any feedback on this approach.

public static class HtmlHelperExtensions {
    public static void RenderSubAction<TController>(this HtmlHelper helper, 
            Expression<Action<TController>> action)
        where TController : Controller {
        RouteValueDictionary routeValuesFromExpression = ExpressionHelper

            .GetRouteValuesFromExpression(action);
        helper.RenderRoute(routeValuesFromExpression);
    }

    public static void RenderSubAction(this HtmlHelper helper, string actionName) {
        helper.RenderSubAction(actionName, null);
    }

    public static void RenderSubAction(this HtmlHelper helper, string actionName, string controllerName) {
        helper.RenderSubAction(actionName, controllerName, null);
    }

    public static void RenderSubAction(this HtmlHelper helper, string actionName, string controllerName, 
            object routeValues) {
        helper.RenderSubAction(actionName, controllerName, new RouteValueDictionary(routeValues));
    }

    public static void RenderSubAction(this HtmlHelper helper, string actionName, string controllerName,
                                    RouteValueDictionary routeValues) {
        RouteValueDictionary dictionary = routeValues != null ? new RouteValueDictionary(routeValues) 
            : new RouteValueDictionary();
        foreach (var pair in helper.ViewContext.RouteData.Values) {
            if (!dictionary.ContainsKey(pair.Key)) {
                dictionary.Add(pair.Key, pair.Value);
            }
        }
        if (!string.IsNullOrEmpty(actionName)) {
            dictionary["action"] = actionName;
        }
        if (!string.IsNullOrEmpty(controllerName)) {
            dictionary["controller"] = controllerName;
        }
        helper.RenderRoute(dictionary);
    }

    public static void RenderRoute(this HtmlHelper helper, RouteValueDictionary routeValues) {
        var routeData = new RouteData();
        foreach (var pair in routeValues) {
            routeData.Values.Add(pair.Key, pair.Value);
        }
        HttpContextBase httpContext = new OverrideRequestHttpContextWrapper(HttpContext.Current);
        var context = new RequestContext(httpContext, routeData);
        bool validateRequest = helper.ViewContext.Controller.ValidateRequest;
        new RenderSubActionMvcHandler(context, validateRequest).ProcessRequestInternal(httpContext);
    }

    #region Nested type: RenderSubActionMvcHandler

    private class RenderSubActionMvcHandler : MvcHandler {
        private bool _validateRequest;
        public RenderSubActionMvcHandler(RequestContext context, bool validateRequest) : base(context) {
            _validateRequest = validateRequest;
        }

        protected override void AddVersionHeader(HttpContextBase httpContext) {}

        public void ProcessRequestInternal(HttpContextBase httpContext) {
            AddVersionHeader(httpContext);
            string requiredString = RequestContext.RouteData.GetRequiredString("controller");
            IControllerFactory controllerFactory = ControllerBuilder.Current.GetControllerFactory();
            IController controller = controllerFactory.CreateController(RequestContext, requiredString);
            if (controller == null)
            {
                throw new InvalidOperationException(string.Format(CultureInfo.CurrentUICulture, 
                    "The IControllerFactory '{0}' did not return a controller for a controller named '{1}'.", 
                    new object[] { controllerFactory.GetType(), requiredString }));
            }
            try
            {
                ((ControllerBase) controller).ValidateRequest = _validateRequest;
                controller.Execute(RequestContext);
            }
            finally
            {
                controllerFactory.ReleaseController(controller);
            }
        }
    }

    private class OverrideHttpMethodHttpRequestWrapper : HttpRequestWrapper {
        public OverrideHttpMethodHttpRequestWrapper(HttpRequest httpRequest) : base(httpRequest) { }

        public override string HttpMethod {
            get { return "GET"; }
        }
    }

    private class OverrideRequestHttpContextWrapper : HttpContextWrapper {
        private readonly HttpContext _httpContext;
        public OverrideRequestHttpContextWrapper(HttpContext httpContext) : base(httpContext) {
            _httpContext = httpContext;
        }

        public override HttpRequestBase Request {
            get { return new OverrideHttpMethodHttpRequestWrapper(_httpContext.Request); }
        }
    }

    #endregion
}

In Part 1 we looked at how to create a full-text index of NHibernate persisted domain objects using the Lucene.NET project. Part 2 then looked at how to query the index complete with query-parsing and hit-highlighting of the results.

Now that we have a full-text index there are other things that we can use it for. The easiest and most useful is probably adding a 'similar items' feature where the system can automatically display related items based on the text that they share in common. While it isn't exact the results are often surprisingly good and while a human editor could probably pick out some links with more finesse it can quickly become an impossible task as the number of items grow - the human will typically resort to searching for similar items using the index anyway so why not automate it?!

This feature can be used to display related web pages or blog entries or, in this case, related books. It probably isn't too far off from the system that Amazon uses. The benefit is that as new content is being added, the top related items can constantly be updated - even for existing items in the system. So, for example, if a new Harry Potter book is released then the existing books can immediately start linking to it and vice-versa or if a company starts offering a new training course or product then any related pages will immediately start to link together.

While it sounds complicated, it is actually quite easy thanks to the contrib assemblies provided with Lucene.NET. In fact, it's so simple it's almost trivial so this won't be a long post!

First, we need to add a new reference to the SimilarityNet.dll assembly (part of Lucene.NET contrib). This provides a SimilarityQueries class which contains a FormSimilarQuery method. Calling this will a piece of text (from an existing field), an analyzer and the field name will produce a boolean query using every unique word where all words are optional. If we repeat this with each field, boosting the relevance of the most important ones (such as title) then we end up with a query that will look for every word in each field of the original item.

To quote the Lucene documentation:

The philosophy behind this method is "two documents are similar if they share lots of words". Note that behind the scenes, Lucene's scoring algorithm will tend to give two documents a higher similarity score if the share more uncommon words.

What this means in practice is that the more unique a word is, the more likely it will be taken into account when ranking the similar items. So, if our original book has 'Agile' in the title and words such as 'scrum' and 'backlog' in the summary then chances are we will find other books that also have these more unique words ... and it's very likely that they will be related to our original book.

Of course, when we search our index for books with all these words there is going to be one obvious match - the original book! In fact, this should be the first result returned so we could either skip this when creating the result-set (looking for the same unique Id rather than just skipping the first one just to be safe) or, as in the example below, use a boolean search and specifically exclude the Id of the source item from the query. I haven't experimented to see which one is quicker but I prefer to let Lucene do all the work - I trust it and it saves me writing any more code or getting results back that I am just going to discard which feels wrong.

Here is the code to find the best 4 similar matches to any book passed in. Note that I include the Authors and Publisher fields when doing the comparison so it will tend to favour books by the same author or publisher - you will need to experiment to see what makes most sense for your application and usage.

/// <summary>
/// Gets similar books.
/// </summary>
/// <param name="book">The book.</param>
/// <returns></returns>
public override IList<IBook> GetSimilarBooks(IBook book)
{
    IFullTextSession session = (IFullTextSession)NHibernateHelper.GetCurrentSession();
    Analyzer analyzer = new StandardAnalyzer();
    BooleanQuery query = new BooleanQuery();

    Query title = Similarity.Net.SimilarityQueries.FormSimilarQuery(book.Title, analyzer, "Title", null);
    title.SetBoost(10);
    query.Add(title, BooleanClause.Occur.SHOULD);

    if (book.Summary != null) {
        Query summary =
            Similarity.Net.SimilarityQueries.FormSimilarQuery(book.Summary, analyzer, "Summary", null);
        summary.SetBoost(5);
        query.Add(summary, BooleanClause.Occur.SHOULD);
    }

    if (book.Authors != null) {
        Query authors =
            Similarity.Net.SimilarityQueries.FormSimilarQuery(book.Authors, analyzer, "Authors", null);
        query.Add(authors, BooleanClause.Occur.SHOULD);
    }

    if (book.Publisher != null) {
        Query publisher =
            Similarity.Net.SimilarityQueries.FormSimilarQuery(book.Publisher, analyzer, "Publisher", null);
        query.Add(publisher, BooleanClause.Occur.SHOULD);
    }

    // avoid the book being similar to itself!
    query.Add(new TermQuery(new Term("Id", book.Id.ToString())), BooleanClause.Occur.MUST_NOT);

    IQuery nhQuery = session.CreateFullTextQuery(query, new Type[] { typeof(Book) })
                            .SetMaxResults(4);

    IList<IBook> books = nhQuery.List<IBook>();
    return books;
}

That about wraps it up for using NHibernate and Lucene. I'm expecting things to change when the new NHibernate version 2.0 is released so I'll probably post again to update you of any changes though when it is. Also, there are a few other features available in Lucene which I may blog about such as using Synonyms for the 'did you mean ...' type suggestions.

Please let me know if there is anything that I haven't explained particularly well or you would like to see more about.

In NHibernate.Search using Lucene.NET Full Text Index (Part 1) we looked at setting up the NHibernate.Search extension to add full-text searching of NHibernate-persisted objects.

Next, we'll look at how we can perform Google-like searches using the Lucene.NET index and some tips on displaying the results including highlighting the search-terms.

Our Book class has the Title, Summary, Authors and Publisher field indexed so we'll allow searching in any of these fields. However, if a search-term exists in the title it is probably more relevant than if it just exists in the summary so we want to give more priority to certain fields than to others. Likewise, we probably want to be able to specify which fields to search on otherwise we would get books that make mention of "Martin Fowler" in the summary whereas we may want to only see books that have "Martin Fowler" as an author for example.

Also worth mentioning is the Summary field. In the Book class there is a SummaryHtml field which (you'll never guess) contains the Html summary retrieved from Amazon and also a Summary field which is the one that is actually indexed. In the full app this text field is generated from the Html content using the HtmlAgility library. The reason we want a version of the Summary in plain text is to make indexing easier / more accurate (no HTML tags) and also to allow result fragments to be created: imagine if a section of the SummaryHtml was output - it could potentially split across an Html element or attribute (producing invalid markup) or include the opening tag but not the matching closing one (producing runaway bold-text for instance).

Back to our example though. To be able to show the highlighted search terms in the results I found it easier to create a special BookSearchResult class that I can return from the data provider - the highlighting is something Lucene.NET can do for us and avoids us having to write our own presentation code to handle it. Here is the class:

/// <summary>
/// A wrapper for a book object returned from a full text index query
/// with additional properties for highlighted segments
/// </summary>
public class BookSearchResult : IBookSearchResult
{
    private readonly IBook _book;
    private string _highlightedTitle;
    private string _highlightedSummary;
    private string _highlightedAuthors;
    private string _highlightedPublisher;

    /// <summary>
    /// Initializes a new instance of the <see cref="BookSearchResult"/> class.
    /// </summary>
    /// <param name="book">The book.</param>
    public BookSearchResult(IBook book)
    {
        _book = book;
    }

    /// <summary>
    /// Gets the book.
    /// </summary>
    /// <value>The book.</value>
    public IBook Book
    {
        get { return _book; }
    }

    /// <summary>
    /// Gets or sets the highlighted title.
    /// </summary>
    /// <value>The highlighted title.</value>
    public string HighlightedTitle
    {
        get
        {
            if (_highlightedTitle == null || _highlightedTitle.Length == 0)
            {
                return _book.Title;
            }
            return _highlightedTitle;
        }
        set { _highlightedTitle = value; }
    }

    /// <summary>
    /// Gets or sets the highlighted summary.
    /// </summary>
    /// <value>The highlighted summary.</value>
    public string HighlightedSummary
    {
        get
        {
            if (_highlightedSummary == null || _highlightedSummary.Length == 0)
            {
                if (_book.Summary == null || _book.Summary.Length < 300)
                {
                    return _book.Summary;
                }
                else
                {
                    return _book.Summary.Substring(0,300) + " ...";
                }
            }
            return _highlightedSummary;
        }
        set { _highlightedSummary = value; }
    }

    /// <summary>
    /// Gets or sets the highlighted authors.
    /// </summary>
    /// <value>The highlighted authors.</value>
    public string HighlightedAuthors
    {
        get
        {
            if (_highlightedAuthors == null || _highlightedAuthors.Length == 0)
            {
                return _book.Authors;
            }
            return _highlightedAuthors;
        }
        set { _highlightedAuthors = value; }
    }

    /// <summary>
    /// Gets or sets the highlighted publisher.
    /// </summary>
    /// <value>The highlighted publisher.</value>
    public string HighlightedPublisher
    {
        get
        {
            if (_highlightedPublisher == null || _highlightedPublisher.Length == 0)
            {
                return _book.Publisher;
            }
            return _highlightedPublisher;
        }
        set { _highlightedPublisher = value; }
    }
}

You'll notice that the Highlighted... fields return the equivalent book field if the highlighted field does not exist. This just saves us having to check whether there is a highlighted term in each field when we're building the search result list.

Our data provider will accept a single string consisting of the entered search-terms and return a list of BookSearchResult objects that match. Here is the code and I'll then try and explain what it's doing:

/// <summary>
/// Finds the books.
/// </summary>
/// <param name="query">The query.</param>
/// <returns></returns>
public override IList<IBookSearchResult> FindBooks(string query)
{
    IList<IBookSearchResult> results = new List<IBookSearchResult>();

    Analyzer analyzer = new SimpleAnalyzer();
    MultiFieldQueryParser parser = new MultiFieldQueryParser(
                                   new string[] { "Title", "Summary", "Authors", "Publisher"}, 
                                   analyzer);
    Query queryObj;

    try
    {
        queryObj = parser.Parse(query);
    }
    catch (ParseException)
    {
        // TODO: provide feedback to user on failed search expressions
        return results;
    }

    IFullTextSession session = (IFullTextSession) NHibernateHelper.GetCurrentSession();
    IQuery nhQuery = session.CreateFullTextQuery(queryObj, new Type[] {typeof (Book) } );
    
    IList<IBook> books = nhQuery.List<IBook>();

    IndexReader indexReader = IndexReader.Open(SearchFactory.GetSearchFactory(session)
                                         .GetDirectoryProvider(typeof (Book)).Directory);
    Query simplifiedQuery = queryObj.Rewrite(indexReader);
    
    SimpleHTMLFormatter formatter = new SimpleHTMLFormatter("<b class='term'>", "</b>");

    Highlighter hTitle = GetHighlighter(simplifiedQuery, formatter, "Title", 100);
    Highlighter hSummary = GetHighlighter(simplifiedQuery, formatter, "Summary", 200);
    Highlighter hAuthors = GetHighlighter(simplifiedQuery, formatter, "Authors", 100);
    Highlighter hPublisher = GetHighlighter(simplifiedQuery, formatter, "Publisher", 100);

    foreach(IBook book in books)
    {
        IBookSearchResult result = new BookSearchResult(book);

        TokenStream tsTitle = analyzer.TokenStream("Title", 
                              new System.IO.StringReader(book.Title ?? string.Empty));
        result.HighlightedTitle = hTitle.GetBestFragment(tsTitle, book.Title);

        TokenStream tsAuthors = analyzer.TokenStream("Authors",
                              new System.IO.StringReader(book.Authors ?? string.Empty));
        result.HighlightedAuthors = hAuthors.GetBestFragment(tsAuthors, book.Authors);

        TokenStream tsPublisher = analyzer.TokenStream("Publisher", 
                              new System.IO.StringReader(book.Publisher ?? string.Empty));
        result.HighlightedPublisher = hPublisher.GetBestFragment(tsPublisher, book.Publisher);

        TokenStream tsSummary = analyzer.TokenStream("Summary", 
                              new System.IO.StringReader(book.Summary ?? string.Empty));
        result.HighlightedSummary = hSummary.GetBestFragments(tsSummary, 
                                    book.Summary, 3, " ... <br /><br /> ... ");

        results.Add(result);
    }

    return results;
}

/// <summary>
/// Gets the highlighter for the given field.
/// </summary>
/// <param name="query">The query.</param>
/// <param name="formatter">The formatter.</param>
/// <param name="field">The field.</param>
/// <param name="fragmentSize">Size of the fragment.</param>
/// <returns></returns>
private static Highlighter GetHighlighter(Query query, Formatter formatter,
                                          string field, int fragmentSize)
{
    // create a new query to contain the terms
    BooleanQuery termsQuery = new BooleanQuery();

    // extract terms for this field only
    WeightedTerm[] terms = QueryTermExtractor.GetTerms(query, true, field);
    foreach (WeightedTerm term in terms)
    {
        // create new term query and add to list
        TermQuery termQuery = new TermQuery(new Term(field, term.GetTerm()));
        termsQuery.Add(termQuery, BooleanClause.Occur.SHOULD);
    }

    // create query scorer based on term queries (field specific)
    QueryScorer scorer = new QueryScorer(termsQuery);

    Highlighter highlighter = new Highlighter(formatter, scorer);
    highlighter.SetTextFragmenter(new SimpleFragmenter(fragmentSize));

    return highlighter;
}

First, we parse the user-entered query string indicating that we want to match on the fields Title, Summary, Authors and Publisher using the MultiFieldQueryParser. This turns the user entered search expression into Lucene specific instructions. Most users when searching will enter a simple expression containing the words or phrase that they want to find. If the search term "XML' is entered for example Lucene will convert this into the expression "Title:XML Summary:XML Authors:XML Publisher:XML" which effectively means "find any record where 'XML' exists in any of the fields".

The user can enter specific instructions directly such as "Title:Architecture Authors:Fowler" which means "Find any books that have 'Architecture' in the Title field or 'Fowler' in the Authors field". Boolean expressions can be used to control this further allowing "(Title:Architecture) AND (Authors:Fowler)" to find any books titled 'Architecture' authored by 'Fowler'. When specific searches like this have been entered then the MultiFieldQueryParser doesn't expand the search to include all fields (except for un-field-prefixed words and phrases).

Incidentally, in the original Book class we included attributes to control the indexing such as [Boost(10)] for the Title. This boosts the relevance of searches on certain fields so a search for 'XML' in the Title and Summary of a document will rank books with 'XML' in the Title higher than books that have 'XML' in the summary - they are more likely to be what the user is searching for in this case.

Lucene does provide many other ways to define a query but this is simple and easy for this example.

Once we have our Lucene query object we use this to create an NHibernate.Search full-text query to return Book objects. This is where NHibernate and Lucene meet (from a querying point of view). It is possible to combine full-text-queries of Lucene with NHibernate queries of the database - NHibernate.Search handles the searching and returns the relevant objects.

So, we now have a list of Book objects just the same as if it had come directly from NHibernate except that the results are in order based on the rank provided by the Lucene search.

Now, we'll use another part of Lucene to highlight the matches. This is done using the SimpleHTMLFormatter, QueryScorer and Highlighter objects which combined allow us to get a fragment for each field with the search terms highlighted.

Note that the SimpleHtmlFormatter class is not in the main Lucene.Net.dll assembly but instead in a separate contrib assembly called Highlighter.Net.dll - there are also some other interesting utilities worth exploring in the contrib folder of the Lucene.NET distribution. Remember in Part 1 I mentioned that I had problems with assembly references and different versions of Lucene.Net.dll being used by NHibernate.Search so if you have problems building the solution after adding references to these contrib assemblies, consider building NHibernate.Search making sure that it references the same Lucene.Net.dll as the Lucene contrib assemblies were built against.

The Highlighter object for each field has to be based on the query terms for that field only so the original query is re-written and split up so that only the terms searched for that field are used. This isn't strictly necessary but I think it makes more sense if when you search for 'Microsoft' in the Title of a book only that occurrences of 'Microsoft' in the Summary or Publisher fields are not highlighted: the highlighted results then show clearly which found terms influenced the results. I have split this functionality into a separate GetHighlighter() method.

For example, without doing this a search for 'Title:Microsoft' incorrectly highlights the occurrences of 'Microsoft' found within the Author, Publisher and Summary fields even though they did not really contribute to the Book being included in the results or it's rank within them:

By creating the proper Highlighter for each field based on the terms used to search it the search results can be shown correctly without highlighting the un-searched fields / terms:

Also, not that the fragments produced for the Summary are different - if a separate terms are used for the Title and Summary then having the Title terms highlighted in the Summary would possibly produce incorrect or sub-standard fragments.

Having built our Highlighters we can then iterate over the results creating a BookSearchResult to wrap each book in the result set. The same analyzer used in the initial query is then used to get a TokenStream for each field which the Highlighter instance needs to create the highlighted fragment from.

For the Title, Authors and Publisher fields we return a single Fragment which will normally be the field itself with the highlighted search terms wrapped in <b class='term'> ... </b> Html tags (courtesy of the SimpleHtmlFormatter class). The highlighted Summary is set to the best 3 fragments separated by '... <br /><br /> ... '. However big the summary is this ensures that the results contain a similar sized chunk of text with the best fragments shown (those containing the most highlighted terms).

Here is an example of the results for 'Title:Software Summary:Requirements Authors:Steve' after formatting and CSS applied to show the highlighted terms in yellow:

Lucene.NET can do a lot more than I've shown here. I found the best resource for learning about how to use it is the 'Lucene in Action' book:

Lucene in Action (In Action series) by Otis Gospodnetic, Erik Hatcher Read more about this book...

Note that this covers the Java version but applies equally well to the .NET port which is practically identical.

I hope this has been useful. In Part 3 I'll try and demonstrate using the Lucene.NET index to find similar items based on the frequency of shared terms. This can be used to provide 'other books you may like' or 'blog posts like this one' type functionality.

This is a little tip that I've found useful when working on projects on different machines.

If you have a desktop machine and separate database server then you generally wouldn't need to have SQL server running locally - either the full version OR the SQL Express edition.

So, within your app the connection string would reference the name of the server, e.g.:

The problem is of course when you checkout this code on another machine such as a laptop when working on-the-road (or just down in the basement while watching an episode of 'Lost' )

Sure, you can just change the config to say '(local)' or '(local)\SQL2005' or whatever ... but you run into issues with the file being changed and then having to change it back if you check it in.

Urgh.

The simplest solution I've found is to setup an Alias using the SQL Server Configuration Manager:

• On the desktop machine, setup an alias called 'dbserver' pointing to the proper database server.
• On the laptop machine, setup the same alias called 'dbserver' this time pointing to the local instance.

Now, the same connection string can be run on both machines (using 'Data Source=dbserver' in the connection string) without having to worry about changing it when checking it out and not checking it in if you changed it.

NOTE: I usually generate the database schema from the C# classes and NHibernate mapping file and include a data-setup tool so it isn't an issue having two separate databases and normally most of the work is on the actual application and not so much on the database schema.

Ayende added the NHibernate.Search last year but I've never seen a great deal of documentation or examples around it so hopefully this post will help others to get started with it.

Basically, this addition to NHibernate brings two of the best open source libraries together - NHibernate as the Object Relational Mapper that persists your objects to a database and Lucene.NET which provides full-text indexing and query support.

So how do you use it?

The first problem you will run into is actually finding it. Unfortunately the release of NHibernate does not include it in the \bin although it is there in the source. Download the latest version of the NHibernate source (1.2.1 GA as of writing) and compile it to produce the NHibernate.Search.dll assembly.

Before you do this though, you may want to also download the latest Lucene.NET release (2.0.004) and replace the Lucene.NET.dll assembly in the NHibernate \lib\net\2.0 folder (I'm assuming you are using .NET 2.0). While the Lucene.NET library has the same version number and did work fine, the sizes are different and I ran into some problems when trying to use some of the extra Lucene.NET assemblies for hit-highlighting and similarity matching.

The first step is of course to add a reference to NHibernate.Search.dll to your Visual Studio.NET Project.

Next, you need to add some additional properties to the session-factory element of the NHibernate configuration section(normally stored in your web.config file):

<property name="hibernate.search.default.directory_provider">NHibernate.Search.Storage.FSDirectoryProvider, NHibernate.Search</property><property name="hibernate.search.default.indexBase">~/Index</property>

If you've used Lucene.NET much you will know that it has the concept of different directory providers for storing the indexed such as RAM or FS (File System). The entries above are used to indicate that we want the Lucene index to be stored on the file system and located in the /Index folder of the website (it could of course be outside the website mapped folder). It's well worth reading a book such as Lucene in Action to get a good idea of how Lucene works and what it can do (it's for the Java version but is still excellent for learning the .NET implementation).

The next step requires that you decorate your C# class with some attributes to control the indexing operation. Personally, I don't like this as it means I need to start referencing NHibernate and Lucene assemblies from my otherwise nice, clean POCO (Plain Old CLR/C# Classes) project. It would have been much nicer IMO if this information could have been put in the NHibernate .hbm.xml mapping files but it's a small price to pay and some people already use the attribute approach for NHibernate anyway.

Here is an example of a Book class for a library application with the additional attributes:

[Indexed(Index = "Book")] public class Book : IBook {     private Guid _id;     private string _title;     private string _summary;     private string _summaryHtml;     private string _authors;     private string _url;     private string _smallImageUrl;     private string _mediumImageUrl;     private string _largeImageUrl;     private string _isbn;     private string _published;     private string _publisher;     private string _binding;     [DocumentId]     [FieldBridge(typeof(GuidBridge))]     public Guid Id     {         get { return _id; }         set { _id = value; }     }     [Field(Index.Tokenized, Store = Store.No)]     [Analyzer(typeof(StandardAnalyzer))]     [Boost(2)]     public string Title     {         get { return _title; }         set { _title = value; }     }     [Field(Index.Tokenized, Store = Store.No)]     [Analyzer(typeof(StandardAnalyzer))]     public string Summary     {         get { return _summary; }         set { _summary = value; }     }     public string SummaryHtml     {         get         {             if (_summaryHtml == null || _summaryHtml.Length == 0)             {                 return _summary;             }             return _summaryHtml;         }         set { _summaryHtml = value; }     }     [Field(Index.Tokenized, Store = Store.No)]     [Analyzer(typeof(StandardAnalyzer))]     public string Authors     {         get { return _authors; }         set { _authors = value; }     }     public string Url     {         get { return _url; }         set { _url = value; }     }     public string SmallImageUrl     {         get { return _smallImageUrl; }         set { _smallImageUrl = value; }     }     public string MediumImageUrl     {         get { return _mediumImageUrl; }         set { _mediumImageUrl = value; }     }     public string LargeImageUrl     {         get { return _largeImageUrl; }         set { _largeImageUrl = value; }     }     [Field(Index.UnTokenized, Store = Store.Yes)]     public string Isbn     {         get { return _isbn; }         set { _isbn = value; }     }     [Field(Index.UnTokenized, Store = Store.No)]     public string Published     {         get { return _published; }         set { _published = value; }     }     [Field(Index.Tokenized, Store = Store.No)]     [Analyzer(typeof(StandardAnalyzer))]     public string Publisher     {         get { return _publisher; }         set { _publisher = value; }     }     public string Binding     {         get { return _binding; }         set { _binding = value; }     } } 

Now we're ready to start using it from NHibernate. To do this we need to create a FullTextSession and use this instead of the regular NHibernate Session (which it wraps / extends):

ISession session = sessionFactory.OpenSession(new SearchInterceptor());IFullTextSession fullTextSession = Search.CreateFullTextSession(session);

And that's it. You can use the IFullTextSession in place of the regular ISession (even casting it for places where you are just doing normal NHibernate operations). All the magic happens inside NHibernate.Search - when you add, update or delete records the 'documents' in the Lucene index are automatically updated which provides you with an excellent Full Text index without a Windows Service in sight!

You can check that it's working by looking in the Index folder - there should be a 'Book' folder containing the Lucene index files (with CFS extensions).

In the next post I'll demonstrate using the index to do some queries including hit-highlighting for presenting the results but for now you may want to download and try Luke - a Java program to browser Lucene index catalogs (the file format is identical between the two implementations).

I recently inherited an application to work on which for whatever reason didn't have the code-behind files linked with the corresponding .aspx and .ascx files.

Visual studio looks for a codefile="class.cs" attribute in the page or control directive and this was missing.

So, when opening the application in Visual Studio the list of files was twice as long as it should have been and prevented Visual Studio from working some of it's magic like it does.

There were hundreds of files and editing each one to add the codefile="..." attribute to each page or control tag would have taken far too long.

What is the quickest way of turning this:

<%@ page language="c#" inherits="Company.Application.Class, Assembly" theme="Default" %>

... into this:

<%@ page language="c#" inherits="Company.Application.Class, Assembly" theme="Default" CodeBehind="Class.aspx.cs" %>

? Regular expressions of course !

Visual Studio can do search and replace and provides it own Regular Expression syntax that can be used (slightly different to most other versions strangely including the .NET framework itself but it works).

In case anyone needs to do this the syntax I used was:

Find what:
^{\<\%\@:bpage.+inherits=\"}{.+}\.{.+}\,{.+\"}{.+}$

Replace with:
\1\2.\3,\4 Codebehind="\3.aspx.cs"\5

Not forgetting to make sure that the 'Use:' option has 'Regular Expressions' selected.

Now, one click of the 'Replace All' button and the files were re-associated (after saving and re-opening the project).

For controls, I just replaced the 'page' part of the Find text with 'control'.

If you don't use a namespace then you may need to tweak the regex's a little but hopefully this should save you some work.

This is an old project I came across while seaching for a different project called Html2Image (which, given a URL would produce an image of the rendered page). I can only describe this as a 'stupid web trick' although there may be some uses for it. This one will take an image file and convert it to HTML.

Not to an HTML <img src="theimage.gif"/> tag though, to actual HTML - each pixel is an HTML element with the background color coming from a 'palette' of CSS styles. This is done to try and reduce the size of the generated XHTML and some RLE (Run Length Encoding) is also used to shrink repeated pixels of the same color to a single element entry in the output. For large images the output size will be prohibitive but for small images and icons it becomes more usable.

The net result is that you see the same image on the screen in the browser (or in an email client?) even if images are turned off. I did some experiments (again, several years ago) and it was possible to have richer-looking emails without needing images but again, things may have moved on and it may not be viable anymore.

The original project (at least 3 or 4 years years old) used <p> elements for each pixel but browsers must have moved on (and XHTML rendering is different to ye-olde-HTML) so I had to change the element tags to make it work again. It runs ok on IE and Safari but Mozilla / Firefox doesn't render it as it is (I honestly really don't know why people rave about it). I'm sure a bit of playing around with different element types and CSS attributes (line-height, font-size etc...) will produce something that runs. It may require different element types on different browsers (to cater for browsers that refuse to render empty elements and such like) but the approach will be the same.

Here are some screenshots of an example page which shows the same image displayed as a regular XHTML <img> tag and also as XHTML ...

Internet Explorer:

Safari:

Source Code: 

The VS.NET 2008 project is downloadable from the bottom of this post but here is the actual class that does the work and is usable in any version of the .NET runtime:

Enjoy!

Download source: Image2Html.zip (8.23 kb)

The normal behavior for .NET 2.0 applications compiled with the default 'Any CPU' platform is to run as 32-bit on x86 (32-bit) Windows and as 64-bit on x64 (64-bit) Windows.

Occasionally, some apps won't run correctly - I've recently run into this with CCNetConfig (a CruiseControl.NET Configuration tool) and have seen it before with other tools. Another obscure scenario where it shows up is if you try to use the JET OleDB driver which will fail in 64-bit mode because there isn't one! (it has to be 32-bit).

Rather than have to recompile the app or even worse, run a 32-bit Virtual Machine, there is an easy way to force .NET to run an app in 32-bit mode using the 'CorFlags.exe' tool.

Depending on your system this may be installed in different places. I've seen it in different places on XP64 and Vista X64:

• C:\Program Files\Microsoft SDKs\Windows\v6.0\Bin\x64\CorFlags.exe
• C:\Program Files (x86)\Microsoft Visual Studio 8\SDK\v2.0\Bin\CorFlags.exe

Running this from the command line with the path / filename of the app you want to change and the switch /32BIT+ to turn on 32-bit mode, e.g.:

   CoreFlags.exe TheApp.exe /32BIT+ 

If that fixes the problem then you know that it is a 64-bit issue. You can re-enable 64-bit operation for the app by turning off the 32-bit switch with the parameter /32BIT-, e.g.:

   CoreFlags.exe TheApp.exe /32BIT- 

Voila ... control over 32-bit and 64-bit execution without doing a recompile! I'm not 100% certain but I think that this switch sets the same flag that the 'x86' and 'Any CPU' targets set in Visual Studio.