Setting sub object property with ILGenerator.Emit
I have some code that uses IlGenerator.Emit to create and populate a generic object using a datareader. It works great, but I need to extend it to populate simple child objects when the database field name contains an underscore character.
For example, a database field named "Address_Line1" should populate the Line1 property, which is the Address property of the Entity. In C # code which is basically ...
Entity.Address.Line1 = "value from reader";
I tried writing C # code and used ILSpy to try and identify the IL code I should be writing, but I keep getting memory errors etc.
The code below includes the currently valid IL code and I've included my commented code attempt. Can anyone help me?
public static DynamicBuilder<T> CreateBuilder(IDataRecord reader)
{
var result = new DynamicBuilder<T>();
var method = new DynamicMethod("DynamicCreate", typeof(T), new Type[] { typeof(IDataReader) }, typeof(T), true);
var generator = method.GetILGenerator();
generator.DeclareLocal(typeof(T));
generator.Emit(OpCodes.Newobj, typeof(T).GetConstructor(Type.EmptyTypes));
generator.Emit(OpCodes.Stloc_0);
var getValue = reader.GetType().GetMethod("get_Item", new Type[] { typeof(int) });
for (int i = 0; i < reader.FieldCount; i++)
{
var name = reader.GetName(i).Split('_'); // MY CODE
var propertyInfo = typeof(T).GetProperty(name[0]);
if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
{
var endIfLabel = generator.DefineLabel();
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
generator.Emit(OpCodes.Callvirt, typeof(IDataRecord).GetMethod("IsDBNull"));
generator.Emit(OpCodes.Brtrue, endIfLabel);
generator.Emit(OpCodes.Ldloc_0);
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
generator.Emit(OpCodes.Callvirt, getValue);
if (propertyInfo.PropertyType.Name.ToLower().Contains("nullable"))
generator.Emit(OpCodes.Unbox_Any, GetNullableType(reader.GetFieldType(i)));
else
generator.Emit(OpCodes.Unbox_Any, reader.GetFieldType(i));
// START MY CODE TO GET THE SUB PROPERTY
if (name.Length > 1)
{
generator.Emit(OpCodes.Callvirt, propertyInfo.GetGetMethod());
propertyInfo = propertyInfo.PropertyType.GetProperty(name[1]);
}
// END MY CODE
generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod());
generator.MarkLabel(endIfLabel);
}
}
generator.Emit(OpCodes.Ldloc_0);
generator.Emit(OpCodes.Ret);
result.handler = (Load)method.CreateDelegate(typeof(Load));
return result;
}
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Code like this:
static Entity DynamicCreate(IDataReader reader)
{
var entity = new Entity();
entity.Property = (int)reader[0];
return entity;
}
compiled to IL, which looks exactly the same as the code you are using (nonessential parts omitted):
ldloc.0 // entity
ldarg.0 // reader
ldc.i4.0
callvirt System.Data.IDataRecord.get_Item
unbox.any System.Int32
callvirt UserQuery+Entity.set_Property
But if you add this second resource access:
static Entity DynamicCreate(IDataReader reader)
{
var entity = new Entity();
entity.SubEntity.Property = (int)reader[0];
return entity;
}
Then the IL looks like this:
ldloc.0 // entity
callvirt UserQuery+Entity.get_SubEntity
ldarg.0 // reader
ldc.i4.0
callvirt System.Data.IDataRecord.get_Item
unbox.any System.Int32
callvirt UserQuery+SubEntity.set_Property
Note that the call get_SubEntity
is between ldloc.0
and ldarg.0
and not right before set_Property
as in your code, so you need to move it in your code as well.
The reason your code doesn't work is because IL is a stack based language: when you call a method with no parameters (like the getter property), the object at the top of the stack (which is the result here unbox.any
) will be used like this
, what you don't like here. Basically, your code is trying to do something like:
entity.Property = ((int)reader[0]).SubEntity;
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I suggest not using IL / Emit code at all, as it is difficult to create expressions with it. Try using the new Roslyn to generate delegates instead.
Here are some examples: https://github.com/dotnet/roslyn/wiki/Scripting-API-Samples
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