Using Dapper with SQL Spatial Types as a parameter

dapper orm spatial sql-server-2008

Question

I've got a system which basically has to do a query like this:

SELECT * FROM MyTable WHERE @parameter.STIntersects(MyGeometryColumn)

This is quite simple to do when using vanilla SQL parameters, you just have to create your parameter in a non-typical way (where the builder variable is a SqlGeometryBuilder which I use to create a rectangle):

command.Parameters.Add(new SqlParameter
{
    UdtTypeName = "geometry",
    Value = builder.ConstructedGeometry,
    ParameterName = "@paremeter"
});

Now, When I try to do this using dapper, I get an error that it can't figure out how to use this as a parameter. Anyone who has got this working, or any pointers on how to enable this? I do have a workaround, but that involves using the string representation and converting that to a geometry type in my SQL query. I really don't want that.

To answer the comment, the error I'm getting is 'The member Parameter of type Microsoft.SqlServer.Types.SqlGeometry cannot be used as a parameter value'. In other words, dapper doesn't know how to deal with a SqlGeometry object as a parameter.

Accepted Answer

The key to implementing weird and wonderful DB specific params all boils down to SqlMapper.IDynamicParameters

This simple interface has a single endpoint:

public interface IDynamicParameters
{
    void AddParameters(IDbCommand command);
}

Dapper already has a DB generic implementation of this interface called: DynamicParameters which allows you to handle output and return values.

To emulate this spatial stuff I would try something like:

public class SpatialParam : SqlMapper.IDynamicParameters
{
    string name; 
    object val;

    public SpatialParam(string name, object val)
    {
       this.name = name; 
       this.val = val;
    }

    public void AddParameters(IDbCommand command, SqlMapper.Identity identity)
    {
       var sqlCommand = (SqlCommand)command;
       sqlCommand.Parameters.Add(new SqlParameter
       {
          UdtTypeName = "geometry",
          Value = val,
          ParameterName = name
       });
    }
}

Usage:

cnn.Query("SELECT * FROM MyTable WHERE @parameter.STIntersects(MyGeometryColumn)",
  new SpatialParam("@parameter", builder.ConstructedGeometry));

This simple implementation of the interface handles only a single param, but it can easily be extended to handle multiple params, either by passing in from the constructor or adding a helper AddParameter method.


Expert Answer

  • Dapper.EntityFramework 1.26 has support for DbGeography
  • Dapper 1.32 has inbuilt support for SqlGeography
  • Dapper 1.33 has inbuilt support for SqlGeometry
  • Dapper.EntityFramework 1.33 has inbuilt support for DbGeometry
  • Dapper 1.34 has inbuilt support for SqlHierarchyId

So with the latest libraries; it should simply work.



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