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    Querying: Highlighting

    Another feature called Highlighting has been added to RavenDB to enhance the search UX.

    Setup

    public class BlogPost
{
	public string Id { get; set; }

	public string Title { get; set; }

	public string Category { get; set; }

	public string Content { get; set; }

	public DateTime PublishedAt { get; set; }

	public string[] Tags { get; set; }

	public BlogComment[] Comments { get; set; }
}
    public class BlogComment
{
	public string Title { get; set; }

	public string Content { get; set; }
}

    public class BlogPosts_ByContent : AbstractIndexCreationTask<BlogPost>
{
    public class Result
    {
        public string Content { get; set; }
    }

    public BlogPosts_ByContent()
    {
        Map = posts => from post in posts
                       select new Result
                       {
                           Content = post.Content
                       };

        Index(x => x.Content, FieldIndexing.Search);
        Store(x => x.Content, FieldStorage.Yes);
        TermVector(x => x.Content, FieldTermVector.WithPositionsAndOffsets);
    }
}

    Important

    Each of the fields on which we want to use Highlighting needs to have:

    • FieldIndexing set to Search
    • FieldStorage set to Yes
    • FieldTermVector set to WithPositionsAndOffsets

    Usage

    To use Highlighting we just need to use one of the Highlight query methods. The basic usage can be as simple as: 

    BlogPost[] results = session
    .Advanced
    .DocumentQuery<BlogPost, BlogPosts_ByContent>()
    .Highlight("Content", 128, 1, out Highlightings highlightings)
    .Search("Content", "raven")
    .ToArray();

StringBuilder builder = new StringBuilder()
    .AppendLine("<ul>");

foreach (BlogPost result in results)
{
    string[] fragments = highlightings.GetFragments(result.Id);
    builder.AppendLine($"<li>{fragments.First()}</li>");
}

string ul = builder
    .AppendLine("</ul>")
    .ToString();

    This will return the list of results and for each result we will be displaying first found fragment with the length up to 128 characters.

    Highlighting + Projections

    Highlighting can also be done when projections are performed.

    BlogPosts_ByContent.Result[] results = session
    .Query<BlogPosts_ByContent.Result, BlogPosts_ByContent>()
    .Highlight("Content", 128, 1, new HighlightingOptions
    {
        PreTags = new[] { "**" },
        PostTags = new[] { "**" }
    }, out Highlightings highlightings)
    .Search(x => x.Content, "raven")
    .ProjectInto<BlogPosts_ByContent.Result>()
    .ToArray();
    BlogPosts_ByContent.Result[] results = session
    .Advanced
    .DocumentQuery<BlogPost, BlogPosts_ByContent>()
    .Highlight("Content", 128, 1, new HighlightingOptions
    {
        PreTags = new[] { "**" },
        PostTags = new[] { "**" }
    }, out Highlightings highlightings)
    .Search("Content", "raven")
    .SelectFields<BlogPosts_ByContent.Result>()
    .ToArray();
    public class BlogPosts_ByContent : AbstractIndexCreationTask<BlogPost>
{
    public class Result
    {
        public string Content { get; set; }
    }

    public BlogPosts_ByContent()
    {
        Map = posts => from post in posts
                       select new Result
                       {
                           Content = post.Content
                       };

        Index(x => x.Content, FieldIndexing.Search);
        Store(x => x.Content, FieldStorage.Yes);
        TermVector(x => x.Content, FieldTermVector.WithPositionsAndOffsets);
    }
}

    Highlighting + Map-Reduce

    Highlighting can be performed when executing queries on map-reduce indexes.

    // highlighting 'Content', but marking 'Category' as key
BlogPosts_ByCategory_Content.Result[] results = session
    .Query<BlogPosts_ByCategory_Content.Result, BlogPosts_ByCategory_Content>()
    .Highlight("Content", 128, 1, new HighlightingOptions
    {
        PreTags = new[] { "**" },
        PostTags = new[] { "**" },
        GroupKey = "Category"
    }, out Highlightings highlightings)
    .Search(x => x.Content, "raven")
    .ToArray();

// get fragments for 'News' category
var newsHighlightings = highlightings.GetFragments("News");
    // highlighting 'Content', but marking 'Category' as key
BlogPosts_ByCategory_Content.Result[] results = session
    .Advanced
    .DocumentQuery<BlogPosts_ByCategory_Content.Result, BlogPosts_ByCategory_Content>()
    .Highlight("Content", 128, 1, new HighlightingOptions
    {
        PreTags = new[] { "**" },
        PostTags = new[] { "**" },
        GroupKey = "Category"
    }, out Highlightings highlightings)
    .Search("Content", "raven")
    .ToArray();

// get fragments for 'News' category
var newsHighlightings = highlightings.GetFragments("News");
    public class BlogPosts_ByCategory_Content : AbstractIndexCreationTask<BlogPost, BlogPosts_ByCategory_Content.Result>
{
    public class Result
    {
        public string Category { get; set; }

        public string Content { get; set; }
    }

    public BlogPosts_ByCategory_Content()
    {
        Map = posts => from post in posts
                       select new Result
                       {
                           Category = post.Category,
                           Content = post.Content
                       };

        Reduce = results => from result in results
                            group result by result.Category into g
                            select new
                            {
                                Category = g.Key,
                                Content = string.Join(" ", g.Select(r => r.Content))
                            };

        Index(x => x.Content, FieldIndexing.Search);
        Store(x => x.Content, FieldStorage.Yes);
        TermVector(x => x.Content, FieldTermVector.WithPositionsAndOffsets);
    }
}

    Remarks

    Note

    Default <b></b> tags are coloured and colours are returned in following order:

    •  yellow,
    •  lawngreen,
    •  aquamarine,
    •  magenta,
    •  palegreen,
    •  coral,
    •  wheat,
    •  khaki,
    •  lime,
    •  deepskyblue,
    •  deeppink,
    •  salmon,
    •  peachpuff,
    •  violet,
    •  mediumpurple,
    •  palegoldenrod,
    •  darkkhaki,
    •  springgreen,
    •  turquoise,
    •  powderblue

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