Why is Dapper emitting IL code in CreateTableConstructor?

.net c# dapper il

Question

I'm looking at the excellent Dapper micro-orm, and in the Dapper.Rainbow project, there is some code that creates a table ctor, using IL. I was hoping someone could explain to me what this code is doing - obviously it's dynamically emitting code to create a constructor (or is it code to call a constructor, or both), but what is the code that's being emitted actually creating, and why is this needed?

Here's the code

protected Action<TDatabase> CreateTableConstructor(Type tableType)
{
    var dm = new DynamicMethod("ConstructInstances", null, new Type[] { typeof(TDatabase) }, true);
    var il = dm.GetILGenerator();

    var setters = GetType().GetProperties()
        .Where(p => p.PropertyType.IsGenericType && p.PropertyType.GetGenericTypeDefinition() == tableType)
        .Select(p => Tuple.Create(
                p.GetSetMethod(true),
                p.PropertyType.GetConstructor(new Type[] { typeof(TDatabase), typeof(string) }),
                p.Name,
                p.DeclaringType
         ));

    foreach (var setter in setters)
    {
        il.Emit(OpCodes.Ldarg_0);
        // [db]

        il.Emit(OpCodes.Ldstr, setter.Item3);
        // [db, likelyname]

        il.Emit(OpCodes.Newobj, setter.Item2);
        // [table]

        var table = il.DeclareLocal(setter.Item2.DeclaringType);
        il.Emit(OpCodes.Stloc, table);
        // []

        il.Emit(OpCodes.Ldarg_0);
        // [db]

        il.Emit(OpCodes.Castclass, setter.Item4);
        // [db cast to container]

        il.Emit(OpCodes.Ldloc, table);
        // [db cast to container, table]

        il.Emit(OpCodes.Callvirt, setter.Item1);
        // []
    }

    il.Emit(OpCodes.Ret);
    return (Action<TDatabase>)dm.CreateDelegate(typeof(Action<TDatabase>));
}

Accepted Answer

Basically, it takes all the properties of the current type (which is derived from Database<T>) that look something like:

public Table<SomeEntity> SomeTable { get; private set; }

And creates a delegate that executes code like the following for each such property:

var table = new Table<SomeEntity>(db, "SomeTable");
db.SomeTable = table;


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