PropertyAccess类 Linq.Expressions 实现

    public class PropertyAccess
    {
        public const BindingFlags PropertyBinding = BindingFlags.Public | BindingFlags.Instance | BindingFlags.GetProperty
            //| BindingFlags.DeclaredOnly
            ;

        public readonly Func<object, object> GetValue;
        public readonly Action<object, object> SetValue;

        protected PropertyAccess(string name, bool nullable, PropertyInfo property)
        {
            // target: (object)((({TargetType})instance).{Property}) 
            // preparing parameter, object type 
            ParameterExpression instance = Expression.Parameter(typeof(object), "instance");
            // ({TargetType})instance 
            UnaryExpression instanceCast = Expression.Convert(instance, property.ReflectedType);
            if (property.CanRead)
            {
                // (({TargetType})instance).{Property} 
                MemberExpression propertyAccess = Expression.Property(instanceCast, property);
                // (object)((({TargetType})instance).{Property}) 
                UnaryExpression castPropertyValue = Expression.Convert(propertyAccess, typeof(object));
                // Lambda expression 
                GetValue = Expression.Lambda<Func<object, object>>(castPropertyValue, instance).Compile();
            }
            if (property.CanWrite)
            {
                ParameterExpression propertyValue = Expression.Parameter(typeof(object), "value");
                UnaryExpression propertyValueCast = Expression.Convert(propertyValue, property.PropertyType);
                MethodCallExpression callPropertyValue = Expression.Call(instanceCast, property.GetSetMethod(), propertyValueCast);
                SetValue = Expression.Lambda<Action<object, object>>(callPropertyValue, instance, propertyValue).Compile();
            }
        }

        public object ChangeType(object value)
        {
            return Convert.ChangeType(value, Nullable.GetUnderlyingType(base.EntityProperty.PropertyType) ?? base.EntityProperty.PropertyType);
        }
    }