Extracting matched phrases
ISearchResults<T> provides methods that allow you to combine the original source text with the search results and extract the matched phrases.CreateMatchPhrasesAsync and CreateMatchPhrases
The intent of the ISearchResults<T>.CreateMatchPhrasesAsync methods is to allow you to provide a mechanism by which
LIFTI can retrieve the original source text, from objects or loosely indexed text, and automatically
extract phrases for the matched token locations. Where a multiple tokens are matched in a sequence, they will be combined into
a single phrase.
For the CreateMatchPhrasesAsync<TObject> overloads that create the matched phrases from an indexed object of type TObject,
you can either fetch the objects one at a time, or be provided with a list of keys and fetch all the relevant objects
in bulk. The latter is more efficient if you are having to go to an external source for the data, e.g. using a database
query.
Example
This example demonstrates searching against an index of Book objects:
public class Book
{
public int BookId { get; set; }
public string Title { get; set; }
public string[] Authors { get; set; }
public string Synopsis { get; set; }
}
var bookIndex = new FullTextIndexBuilder<int>() // Books are indexed by their BookId property, which is an int.
.WithObjectTokenization<Book>(
options => options
.WithKey(b => b.BookId)
.WithField("Title", b => b.Title, tokenOptions => tokenOptions.WithStemming())
.WithField("Authors", b => b.Authors)
.WithField("Synopsis", b => b.Synopsis, tokenOptions => tokenOptions.WithStemming()))
.Build();
var results = bookIndex.Search("first | novel");
And then printing the matched phrases from each of the fields to the console window:
foreach (var result in await results.CreateMatchPhrasesAsync(i => books.First(x => x.BookId == i)))
{
Console.WriteLine($"{result.SearchResult.Key} ({result.SearchResult.Score})");
foreach (var fieldPhrase in result.FieldPhrases)
{
Console.Write($" {fieldPhrase.FoundIn}: ");
Console.WriteLine(string.Join(", ", fieldPhrase.Phrases.Select(x => $"\"{x}\"")));
}
}