NHibernate.OData is an OData parser for NHibernate.
The goal of NHibernate.OData is to parse OData query strings and turn them
into ICriteria. It currently implements the
$top sections of the OData specification located at
The availability of stand-alone parsers like these is very limited. At the time
this project was started, the only good parser available was part
of the WCF Web API project http://wcf.codeplex.com/.
This project contains a complete OData parser which applies the filters
of an OData query string to an
IQueryable. This code can be found in the
directory at http://wcf.codeplex.com/SourceControl/BrowseLatest.
However, the license of this source code limits its usage in production
environments. This project was created as an open source alternative.
There are two ways in which NHibernate.OData can be used. If all that is required
is a way to query the database, the
ODataQuery extension method can be used.
This method parses an OData query string and creates an
ICriteria for that
query string on a specific entity:
ICriteria query = session.ODataQuery<Customer>("$filter=substringof('Harry', Name)");
NHibernate.OData requires some caching based on the session factory associated
with the current session. When using the extension methods on
a static shared instance is used to manage this cache. If it is necessary to
manage the lifetime of this cache, the
ODataContext class can be used instead.
Internally the static extension methods on the
ODataParser class route calls
to the shared
ODataService class provides a service for implementing
a full OData service. To use the
ODataService class, a new instance of this
class must be instantiated for an
ISessionFactory and a few configuration
parameters (see the constructor documentation). Queries can then be
executed using the Query method on the
ODataService class which takes a
session, OData path and OData query string.
The demo application which is included in the ZIP file shows how such a service can be implemented with minimal effort. This demo application makes use of NHttp so it can run without a web server available.
The default join type of NHibernate.OData is the inner join type. This may not give
the expected results. If you want the join type to be the left outer join type, call the
overload that takes a configuration object and set the
OuterJoin property to true.
The current implementation does not access metadata while querying. This results in the following limitations:
The cast operator is a no-op except for when casting to integer types. In that case it is converted to a round call;
The isof operator is a no-op.
Also, currently NHibernate.OData is read-only and can only be used to query the database.
Bugs should be reported through github at http://github.com/pvginkel/NHibernate.OData/issues.
NHibernate.OData is licensed under the LGPL 3.