Query spatial data with dapper

c# dapper micro-orm spatial sql-server

Question

I've found some related questions, but the author gave up and went ahead with using stored procedures to do the 'mapping'.

This is actually a continuation question from here

Model

public class Store
{
    public int Id { get; private set; }
    public string Name { get; set; }
    public string Address { get; set; }
    public DbGeography Location { get; set; }
}

Querying

using (SqlConnection conn = SqlHelper.GetOpenConnection())
{
    const string sql = "Select * from Stores";
    return conn.Query<Store>(sql, new { Tenant_Id = tenantId });
}

Dapper doesn't understand spatial data, and as many had said, it wasn't the authors original intention to support vendor specific implementations. But the documentation to extend the Query<T> support is hard to find

Accepted Answer

I have an exploration into this here, for which the following test passes:

class HazGeo
{
    public int Id { get;set; }
    public DbGeography Geo { get; set; }
}
public void DBGeography_SO24405645_SO24402424()
{
    global::Dapper.SqlMapper.AddTypeHandler(typeof(DbGeography), new GeographyMapper());
    connection.Execute("create table #Geo (id int, geo geography)");

    var obj = new HazGeo
    {
        Id = 1,
        Geo = DbGeography.LineFromText("LINESTRING(-122.360 47.656, -122.343 47.656 )", 4326)
    };
    connection.Execute("insert #Geo(id, geo) values (@Id, @Geo)", obj);
    var row = connection.Query<HazGeo>("select * from #Geo where id=1").SingleOrDefault();
    row.IsNotNull();
    row.Id.IsEqualTo(1);
    row.Geo.IsNotNull();
}

class GeographyMapper : Dapper.SqlMapper.TypeHandler<DbGeography>
{
    public override void SetValue(IDbDataParameter parameter, DbGeography value)
    {
        parameter.Value = value == null ? (object)DBNull.Value : (object)SqlGeography.Parse(value.AsText());
        ((SqlParameter)parameter).UdtTypeName = "GEOGRAPHY";
    }
    public override DbGeography Parse(object value)
    {
        return (value == null || value is DBNull) ? null : DbGeography.FromText(value.ToString());
    }
}

It looks viable, but I haven't dotted every i and crossed every t just yet. You're welcome to experiment with that commit locally - I'd love feedback.



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