Dynamic object property populator (without reflection)
- by grenade
I want to populate an object's properties without using reflection in a manner similar to the DynamicBuilder on CodeProject. The CodeProject example is tailored for populating entities using a DataReader or DataRecord. I use this in several DALs to good effect. Now I want to modify it to use a dictionary or other data agnostic object so that I can use it in non DAL code --places I currently use reflection. I know almost nothing about OpCodes and IL. I just know that it works well and is faster than reflection.
I have tried to modify the CodeProject example and because of my ignorance with IL, I have gotten stuck on two lines.
One of them deals with dbnulls and I'm pretty sure I can just lose it, but I don't know if the lines preceding and following it are related and which of them will also need to go.
The other, I think, is the one that pulled the value out of the datarecord before and now needs to pull it out of the dictionary. I think I can replace the "getValueMethod" with my "property.Value" but I'm not sure.
I'm open to alternative/better ways of skinning this cat too.
Here's the code so far (the commented out lines are the ones I'm stuck on):
using System;
using System.Collections.Generic;
using System.Reflection;
using System.Reflection.Emit;
public class Populator<T>
{
private delegate T Load(Dictionary<string, object> properties);
private Load _handler;
private Populator() { }
public T Build(Dictionary<string, object> properties)
{
return _handler(properties);
}
public static Populator<T> CreateBuilder(Dictionary<string, object> properties)
{
//private static readonly MethodInfo getValueMethod = typeof(IDataRecord).GetMethod("get_Item", new [] { typeof(int) });
//private static readonly MethodInfo isDBNullMethod = typeof(IDataRecord).GetMethod("IsDBNull", new [] { typeof(int) });
Populator<T> dynamicBuilder = new Populator<T>();
DynamicMethod method = new DynamicMethod("Create", typeof(T), new[] { typeof(Dictionary<string, object>) }, typeof(T), true);
ILGenerator generator = method.GetILGenerator();
LocalBuilder result = generator.DeclareLocal(typeof(T));
generator.Emit(OpCodes.Newobj, typeof(T).GetConstructor(Type.EmptyTypes));
generator.Emit(OpCodes.Stloc, result);
int i = 0;
foreach (var property in properties)
{
PropertyInfo propertyInfo = typeof(T).GetProperty(property.Key, BindingFlags.Public | BindingFlags.Instance | BindingFlags.IgnoreCase | BindingFlags.FlattenHierarchy | BindingFlags.Default);
Label endIfLabel = generator.DefineLabel();
if (propertyInfo != null && propertyInfo.GetSetMethod() != null)
{
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
//generator.Emit(OpCodes.Callvirt, isDBNullMethod);
generator.Emit(OpCodes.Brtrue, endIfLabel);
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ldarg_0);
generator.Emit(OpCodes.Ldc_I4, i);
//generator.Emit(OpCodes.Callvirt, getValueMethod);
generator.Emit(OpCodes.Unbox_Any, property.Value.GetType());
generator.Emit(OpCodes.Callvirt, propertyInfo.GetSetMethod());
generator.MarkLabel(endIfLabel);
}
i++;
}
generator.Emit(OpCodes.Ldloc, result);
generator.Emit(OpCodes.Ret);
dynamicBuilder._handler = (Load)method.CreateDelegate(typeof(Load));
return dynamicBuilder;
}
}
EDIT:
Using Marc Gravell's PropertyDescriptor implementation (with HyperDescriptor) the code is simplified a hundred-fold. I now have the following test:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using Hyper.ComponentModel;
namespace Test
{
class Person
{
public int Id { get; set; }
public string Name { get; set; }
}
class Program
{
static void Main()
{
HyperTypeDescriptionProvider.Add(typeof(Person));
var properties = new Dictionary<string, object> { { "Id", 10 }, { "Name", "Fred Flintstone" } };
Person person = new Person();
DynamicUpdate(person, properties);
Console.WriteLine("Id: {0}; Name: {1}", person.Id, person.Name);
Console.ReadKey();
}
public static void DynamicUpdate<T>(T entity, Dictionary<string, object> properties)
{
foreach (PropertyDescriptor propertyDescriptor in TypeDescriptor.GetProperties(typeof(T)))
if (properties.ContainsKey(propertyDescriptor.Name))
propertyDescriptor.SetValue(entity, properties[propertyDescriptor.Name]);
}
}
}
Any comments on performance considerations for both TypeDescriptor.GetProperties() & PropertyDescriptor.SetValue() are welcome...
