Mappers - lobodava/artisan-orm GitHub Wiki

Mappers in Artisan.Orm are static classes decorated with MapperFor attribute.

Here is the mapper for User type:

[MapperFor(typeof(User)]
public static class UserMapper   -- Name of a class does not matter
{

Mapper methods work for two directions and each may have two static methods with reserved names:

DataToObject direction — is to read data by SqlDataReader and return an object of MapperFor type or an ObjectRow:
- CreateObject
- CreateObjectRow
ObjectToData direction — is to create DataTable and populate it with an object data (for further passing it as a parameter to a stored procedure):
- CreateDataTable
- CreateDataRow

CreateObject

CreateObject method reads data by SqlDataReader and returns an object of MapperFor type:

public static User CreateObject(SqlDataReader dr)
{
    var i = 0;
    return new User 
    {
        Id     =  dr.GetInt32(i)    ,
        Login  =  dr.GetString(++i) ,
        Name   =  dr.GetString(++i) ,
        Email  =  dr.GetString(++i) 
    };
}

The order and quantity of columns correspond to the select statement:

select Id, Login, Name, Email from dbo.Users;

CreateObjectRow

What is ObjectRow?

CreateObjectRow method reads data by SqlDataReader and returns an ObjectRow:

public static ObjectRow CreateObjectRow(SqlDataReader dr)
{
    var i = 0;
    return new ObjectRow(4)
    {
        /* 0 - Id    = */  dr.GetInt32(i)    ,
        /* 1 - Login = */  dr.GetString(++i) ,
        /* 2 - Name  = */  dr.GetString(++i) ,
        /* 3 - Email = */  dr.GetString(++i)
    };
}

CreateDataTable

CreateDataTable method creates DataTable which corresponds to a user-defined table type already existing in a database by quantity, type and order:

public static DataTable CreateDataTable()
{
    return new DataTable("UserTableType")
        .AddColumn< Int32  >( "Id"     )
        .AddColumn< String >( "Login"  )
        .AddColumn< String >( "Name"   )
        .AddColumn< String >( "Email"  );
}

The corresponding user-defined table type:

create type dbo.UserTableType as table
(
    Id       int           not null  primary key clustered,
    [Login]  varchar(20)   not null  ,
    Name     nvarchar(50)  not null  ,
    Email    varchar(50)   not null  
);

CreateDataRow

CreateDataRow method creates Object[] where items correspond to columns in DataTable by quantity and order:

public static Object[] CreateDataRow(User obj)
{
    if (obj.Id == 0) 
        obj.Id = Int32NegativeIdentity.Next;

    return new object[]
    {
        obj.Id    ,
        obj.Login ,
        obj.Name  ,
        obj.Email
    };
}

CreateDataRow is the right place to:

assign Negative Identity for Id of new objects,
propagate an object Id value to child items in its collections to make a link for a forign key,
assign integer ParentId from Parent object,
control and change data before it gets to a table valued parameter

Examples

See more examples of Mappers in Tests project: