C# bindings for Xapian

The C# bindings for Xapian are packaged in the Xapian namespace and largely follow the C++ API, with the following differences and additions. C# strings and other types are converted automatically in the bindings, so generally it should just work as expected.

The examples subdirectory contains examples showing how to use the C# bindings based on the simple examples from xapian-examples: SimpleIndex.cs, SimpleSearch.cs, SimpleExpand.cs.

Note: the passing of strings from C# into Xapian and back isn't currently zero byte safe. If you try to handle string containing zero bytes, you'll find they get truncated at the zero byte.

Unicode Support

In Xapian 1.0.0 and later, the Xapian::Stem, Xapian::QueryParser, and Xapian::TermGenerator classes all assume text is in UTF-8. If you're using Mono on UNIX with a UTF-8 locale (which is the default on most modern Linux distributions), then Xapian appears to get passed Unicode strings as UTF-8, so it should just work. We tested with Mono 2.6.7 using the Mono C# 2.0 compiler (gmcs).

However, Microsoft and Mono's C# implementations apparently take rather different approaches to Unicode, and we've not tested with Microsoft's implementation. If you try it, please report how well it works (or how badly it fails...)

Method Naming Conventions

Methods are renamed to use the "CamelCase" capitalisation convention which C# normally uses. So in C# you use GetDescription instead of get_description.

Exceptions

Exceptions are thrown as SWIG exceptions instead of Xapian exceptions. This isn't done well at the moment; in future we will throw wrapped Xapian exceptions. For now, it's probably easier to catch all exceptions and try to take appropriate action based on their associated string.

Iterators

The C#-wrapped iterators work much like their C++ counterparts, with operators "++", "--", "==", and "!=" overloaded. E.g.:

   Xapian.MSetIterator m = mset.begin();
   while (m != mset.end()) {
     // do something
     ++m;
   }

Iterator dereferencing

C++ iterators are often dereferenced to get information, eg (*it). In C# these are all mapped to named methods, as follows:

IteratorDereferencing method
PositionIterator GetTermPos()
PostingIterator GetDocId()
TermIterator GetTerm()
ValueIterator GetValue()
MSetIterator GetDocId()
ESetIterator GetTerm()

Other methods, such as MSetIterator.GetDocument(), are available unchanged.

MSet

MSet objects have some additional methods to simplify access (these work using the C++ array dereferencing):

Method nameExplanation
GetHit(index)returns MSetIterator at index
GetDocumentPercentage(index)ConvertToPercent(GetHit(index))
GetDocument(index)GetHit(index).GetDocument()
GetDocumentId(index)GetHit(index).GetDocId()

Non-Class Functions

The C++ API contains a few non-class functions (the Database factory functions, and some functions reporting version information), but C# doesn't allow functions which aren't in a class so these are wrapped as static member functions of abstract classes like so:

Constants

The Xapian::DB_* constants are currently wrapped in a Xapian class within the Xapian namespace, so have a double Xapian prefix! So Xapian::DB_CREATE_OR_OPEN is available as Xapian.Xapian.DB_CREATE_OR_OPEN. The Query::OP_* constants are wrapped a little oddly too: Query::OP_OR is wrapped as Xapian.Query.op.OP_OR. Similarly, QueryParser::STEM_SOME as Xapian.QueryParser.stem_strategy.STEM_SOME. The naming here needs sorting out...

Query

In C++ there's a Xapian::Query constructor which takes a query operator and start/end iterators specifying a number of terms or queries, plus an optional parameter. This isn't currently wrapped in C#.

MatchAll and MatchNothing

In Xapian 1.3.0 and later, these are wrapped as static constants xapian.Query.MatchAll and xapian.Query.MatchNothing.

If you want to be compatible with earlier versions, you can continue to use new xapian.Query("") instead of xapian.Query.MatchAll and new xapian.Query() instead of xapian.Query.MatchNothing.

MatchDecider

Custom MatchDeciders can be created in C#; simply subclass Xapian.MatchDecider, and define an Apply method that will do the work. The simplest example (which does nothing useful) would be as follows:

class MyMatchDecider : Xapian.MatchDecider {
    public override bool Apply(Xapian.Document doc) {
	return true;
    }
}
Last updated $Date: 2005-12-12T02:56:23.742308Z $