Map 'SqlServer.Types.SqlGeometry' into 'Microsoft.Spatial' types for SQL-Server-Independent geography code with dapper

Question

I am using a Sql server database. I have some spatial data (geometry data type). I need to read them in a C# web project using dapper.

In my project I imported Microsoft.Spatial nuget package, that Support OData v4. I think in this way my project should be SQL-Server-Independent.

First problem I have found is understand which data type I should use to map Sql geometry data type. I am trying to use Microsfot.Spatial.Geometry that is an abstract class. But I am not sure.

Then this is the query I am writing and the mapping I am doing with dapper:

string sql = @"SELECT ..., departureAddress.GeometryLocation AS DepartureCoordinates, arrivalAddress.GeometryLocation AS ArrivalCoordinates ...";

var infoResultset = await this._connection.QueryAsync<MyInfoClass, ..., MyInfoClass>(
    sql,
    (request, ...) =>
    {
        /* Nothing about spatial types */

        return result;
    }
);

When I run the project I obtain this error:

Dapper: Error parsing column 3 (DepartureCoordinates=POINT (12.496365500000024 41.9027835) - Object). Unable to cast object of type 'Microsoft.SqlServer.Types.SqlGeometry' to type 'Microsoft.Spatial.Geometry'.

I have also tryed to use Microsoft.Spatial.GeometryPoint but I obtain same error (just the destination type change in the message).

Can anyone help me to solve the mapping? Thank you

Answer 1

I have solved by changing the query and creating a new type handler:

string sql = @"SELECT ..., departureAddress.GeometryLocation.STAsText() AS DepartureCoordinates, arrivalAddress.GeometryLocation.STAsText() AS ArrivalCoordinates ...";

And this is the type handler I have written:

public class GeometryPointTypeHandler : SqlMapper.TypeHandler<GeometryPoint>
{
    //      POINT(X Y)
    //      POINT(X Y Z M)
    public override GeometryPoint Parse(object value)
    {
        if (value == null)
            return null;

        if (!Regex.IsMatch(value.ToString(), @"^(POINT \()(.+)(\))"))
            throw new Exception("Value is not a Geometry Point");

        //Get values inside the brackets
        string geometryPoints = value.ToString().Split('(', ')')[1];

        //Split values by empty space
        string[] geometryValues = geometryPoints.Split(' ');

        double x = this.ConvertToDouble(geometryValues[0]);
        double y = this.ConvertToDouble(geometryValues[1]);

        double? z = null;
        if (geometryValues.Length >= 3)
            z = this.ConvertToDouble(geometryValues[2]);

        double? m = null;
        if (geometryValues.Length >= 4)
            m = this.ConvertToDouble(geometryValues[3]);

        return GeometryPoint.Create(x, y, z, m);
    }

    public override void SetValue(IDbDataParameter parameter, GeometryPoint value)
    {
        throw new NotImplementedException();
    }

    private double ConvertToDouble(string value)
    {
        return double.Parse(value, CultureInfo.InvariantCulture);
    }
}

I have not implemented SetValue because I do not need it.

Finally I added the handler to dapper:

Dapper.SqlMapper.AddTypeHandler(new GeometryPointTypeHandler());