NHibernate.Spatial, spatial extensions for NHibernate, allows you to connect NHibernate to a spatially enabled database and manipulate geometries in HQL or in .NET code using NetTopologySuite, providing you with a fully integrated GIS programming experience.

There is also a similar but independent effort for Java: Hibernate Spatial.

Features: 

• Geometry types: Geometry columns are mapped to .NET geometry types compliant with OGC specifications.
• Dialects: MsSqlSpatial, PostGIS  MySQL and SQL Server 2008 are supported. The most common spatial functions are registered for use within HQL, providing compatible queries among different dialects.
• Criteria: Spatial relations functions such as Intersects, Within, Crosses, etc.
• Projections: Spatial aggregate, analysis and tranformation functions.
• Schema generation: Support for automatic creation and droping of auxiliary data objects (eg. registering of geometry columns in metadata table).
• Metadata mappings: Built-in mappings to spatial metadata through GeometryColumns and SpatialReferenceSystem classes. 

Requirements:

• .NET 2.0
• NHibernate 2.1.2.GA

Installation:

• Download latest sources and build. Copy the binaries to your project's libraries folder.
• In you project, add references to NHibernate.dll, NHibernate.Spatial.dll, NetTopologySuite.dll, GeoAPI.dll and to provider assembly (eg. NHibernate.Spatial.PostGis.dll).