Advanced querying with LIFTI

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As always, you can find the LIFTI project at its CodePlex home:

Until now, the way in which you can query against LIFTI has been pretty basic. If you searched for “apple orange”, you would only get items back that had words starting with both apple and orange in their associated text.

For simple scenarios this is fine, but what if you wanted to search for apple or orange? What if you actually wanted both apple and orange, but they had to be near to each other? Well I have a extra special treat for you this Christmas.

Introducing better, more expressive queries

I’ve just checked in changes to the LIFTI library that will allow you to perform these sort of queries:

Query Meaning
Deployment Items that contain the word deployment exactly*.
doc* Items that contain words that start with doc.
Deployment & document Items that contain both deployment and document.
Deployment document
Deployment ~ doc* Items containing the word deployment near a word that starts with doc.
Deployment ~> document Items containing the word deployment that are followed closely by document.
Deployment » document Items containing the word deployment followed by document anywhere after it.
“the bug catcher” Items that have the words the bug catcher one after another.
“notr* dam*” Items that have a word that start with notr then a word that starts with dam, one after another.
Deploy* ~> (document server)

* “Exactly” is not quite accurate - if you’re using the stemming word splitter, then it will also match other derivatives of the word.

The more things change, the more they stay the same

Don’t panic if you only want the simple search behaviour! LIFTI was created to be really simple to use, with a really simple API, and I haven’t forgotten that. With that in mind, simple searching is still the default behaviour.

In order to use to this shiny new query engine, you need to set the new QueryParser property to an instance of LiftiQueryParser when you create a new FullTextIndexer, like this:

2var index = new FullTextIndexer<customer>(c => c.Biography)
4    QueryParser = new LiftiQueryParser()

(For those interested, the default query parser class is called SimpleQueryParser, unsurprisingly)

Words are boring, show me a picture!

In the Samples folder of the LIFTI solution, you’ll now find a new sample called StackOverflowSample - when you run it, you’ll see something like this:


You can type in the query at the top, and once you press search, 3 things will happen:

  • The titles of any matching questions are shown in the left panel of the search results - clicking on one of these will show the question body on the right. Note that only the text in the body of the article is indexed.
  • A textual version of the query will be shown below your search (this is just the result of a ToString on the parsed query)
  • The time it took to parse and then execute the search is shown under the search results.

This sample application is also included in the latest binaries download (v0.3).

What about the documentation?

Ok, so LIFTI is getting a little more complex and I’m going to have to start finding some time to write the documentation on CodePlex. There’s nothing substantial there at the moment, but I’m hoping to find some time to get something written over the holiday - bear with me!

I hope that someone out there is finding this useful, or at least interesting - I am!

Happy Christmas!