Custom mapping in Dapper

Question

I\'m attempting to use a CTE with Dapper and multi-mapping to get paged results. I\'m hitting an inconvenience with duplicate columns; the CTE is preventing me from having to Na

Answer 1

You can map a column name with another attribute using the ColumnAttributeTypeMapper.

See my first comment on the Gist for further details.

You can do the mapping like

public class Site
{
    public int SiteID { get; set; }
    [Column("SiteName")]
    public string Name { get; set; }
    public string Description { get; set; }
    public List Locations { get; internal set; }
}

public class Location
{
    public int LocationID { get; set; }
    [Column("LocationName")]
    public string Name { get; set; }
    [Column("LocationDescription")]
    public string Description { get; set; }
    public Guid ReportingID { get; set; }
    [Column("LocationSiteID")]
    public int SiteID { get; set; }
}

Mapping can be done using either of the following 3 methods

Method 1

Manually set the custom TypeMapper for your Model once as:

Dapper.SqlMapper.SetTypeMap(typeof(Site), new ColumnAttributeTypeMapper());
Dapper.SqlMapper.SetTypeMap(typeof(Location), new ColumnAttributeTypeMapper());

Method 2

For class libraries of .NET Framework >= v4.0, you can use PreApplicationStartMethod to register your classes for custom type mapping.

using System.Web;
using Dapper;

[assembly: PreApplicationStartMethod(typeof(YourNamespace.Initiator), "RegisterModels")]

namespace YourNamespace
{
    public class Initiator
    {
        private static void RegisterModels()
        {
             SqlMapper.SetTypeMap(typeof(Site), new ColumnAttributeTypeMapper());
             SqlMapper.SetTypeMap(typeof(Location), new ColumnAttributeTypeMapper());
             // ...
        }
    }
}

Method 3

Or you can find the classes to which ColumnAttribute is applied through reflection and set type mappings. This could be a little slower, but it does all the mappings in your assembly automatically for you. Just call RegisterTypeMaps() once your assembly is loaded.

    public static void RegisterTypeMaps()
    {
        var mappedTypes = Assembly.GetAssembly(typeof (Initiator)).GetTypes().Where(
            f =>
            f.GetProperties().Any(
                p =>
                p.GetCustomAttributes(false).Any(
                    a => a.GetType().Name == ColumnAttributeTypeMapper.ColumnAttributeName)));

        var mapper = typeof(ColumnAttributeTypeMapper<>);
        foreach (var mappedType in mappedTypes)
        {
            var genericType = mapper.MakeGenericType(new[] { mappedType });
            SqlMapper.SetTypeMap(mappedType, Activator.CreateInstance(genericType) as SqlMapper.ITypeMap);
        }
    }