Can I specify DB column names for dapper-dot-net mappings?

Question

Is there a way with dapper-dot-net to use an attribute to specify column names that should be used and not the property name?

public class Code
{
    public int Id { get; set; }
    public string Type { get; set; }
    // This is called code in the table.
    public string Value { get; set; }
    public string Description { get; set; }
}

I'd like to be able to name my properties whatever I choose. Our database has no consistent naming convention.

If not with dapper, are there any additional similar options?

Answer 1

You can also check out Dapper-Extensions.

Dapper Extensions is a small library that complements Dapper by adding basic CRUD operations (Get, Insert, Update, Delete) for your POCOs.

It has an auto class mapper, where you can specify your custom field mappings. For example:

public class CodeCustomMapper : ClassMapper<Code>
{
    public CodeCustomMapper()
    {
        base.Table("Codes");
        Map(f => f.Id).Key(KeyType.Identity);
        Map(f => f.Type).Column("Type");
        Map(f => f.Value).Column("Code");
        Map(f => f.Description).Column("Foo");
    }
}

Then you just do:

using (SqlConnection cn = new SqlConnection(_connectionString))
{
    cn.Open();
    var code= new Code{ Type = "Foo", Value = "Bar" };
    int id = cn.Insert(code);
    cn.Close();
}

Keep in mind that you must keep your custom maps in the same assembly as your POCO classes. The library uses reflection to find custom maps and it only scans one assembly.

Update:

You can now use SetMappingAssemblies to register a list of assemblies to scan:

DapperExtensions.SetMappingAssemblies(new[] { typeof(MyCustomClassMapper).Assembly });

Answer 2

If you are using a select statement directly or in a procedure you can just alias the columns.

SELECT code as Value FROM yourTable

Answer 3

Another approach is to just manually map it with the dynamic result.

var codes = conn.Query<dynamic>(...sql and params here...)
                 .Select<dynamic,Code>(s=>new Code{Id = s.Id, Type = s.Type, Value = s.code, Description = s.Description});

Clearly this introduces type-safety scenarios because you are querying on dynamic. Also, you have to manually map columns which is a bummer.

However, I tend to like this approach because it's so darned transparent. You can cast if need be (as is the case with Enums), and basically just do whatever it is you need to do to go from the db recordset to your properties.

Answer 4

For selects, you can add constructors to your classes to perform the mapping. The constructor parameter names must match the table columns.

Below is an example from the source. The table will be correctly mapped to the class.

Table:

CREATE TABLE #Users (Id int, Name varchar(20))

Class:

   class UserWithConstructor
    {
        public UserWithConstructor(int id, string name)
        {
            Ident = id;
            FullName = name;
        }
        public int Ident { get; set; }
        public string FullName { get; set; }
    }