Is such a thing available or doable with Dapper to automatically expand the members of a class

Question

Is there a way to do something like this? Let's say I have two classes:

public class Class_A
{
  public string Name {get;}
  public string Age  {get;}
  public int    Key  {get;}
}
public class Class_B
{
  public string Doors {get;}
  public string Windows  {get;}
  public int    Key  {get;}
}

and then a combined class like this:

public class Class_C
{
  public Class_A CA {get;}
  public Class_B CB {get;}
}

now let's say I am saying

_connection.Query<Class_C>("A SQL that returns results from JOIN of Clas_A and Class_B")

So then it would be able to somehow know what field to map to what. Because otherwise I have to copy paste the fields of those two classes inside the Class_C again like this:

public class Class_C
{
      public string Name {get;}
      public string Age  {get;}
      public string Doors {get;}
      public string Windows {get;}
}

Answer 1

Following your comments, for removing all redundancy you can add a PropertyB to class A and let Dapper to bind that property to the result of your query.

public class A
{
    public string Name { get; set; }
    public string Age { get; set; }
    public int Key { get; set; }
    public B PropertyB { get; set; }
}

public class B
{
    public string Doors { get; set; }
    public string Windows { get; set; }
    public int Key { get; set; }
}

The query is:

SELECT * FROM A INNER JOIN B ON A.[Key] = B.[Key];

Results are fields in this order Name, Age, Key, Doors, Windows, Key.

So if you split by Doors:

• The group on the left is A (Name, Age, Key)
• The group on the right is B (Doors, Windows, Key).

var results = connection.Query<A, B, A>(
        sql,
        (a, b) =>
        {
            a.PropertyB = b;
            return a;
        },
        splitOn: "Doors")
    .Distinct()
    .ToList();

Query<A, B, A> means left is type A, right is type B and the combined result is A generated by the above function.

For more information see documentation Dapper Multi-Mapping Result. There is support for One-To-One mapping and One-to-Many.