Lazy Load not working in 3.5?

ifergus posted on Thursday, May 29, 2008

I've got a very large business object with numerous children. I’m attempting to use lazy loading so that I only need to load the children when necessary. However, I’m finding that the children are always loaded, even when the parent has no code in its DataPortal_Fetch method to populate them.

Is there something that I need to do to suppress this behavior? I’m using the note from your March 10^th posting as a guideline.

http://www.lhotka.net/weblog/CSLANET35CodeReductionWithChildObjects.aspx

RockfordLhotka replied on Thursday, May 29, 2008

Keep in mind that any attempt to read the specified property will trigger the lazy loading. If that property is data bound to any UI element (or a bindingsource) then data binding will read the property as the form is rendered, thus triggering the lazy loading to load immediately.

Or any other code that reads the property, in your object or elsewhere, will trigger the load.

The point being that the technique is great, but only if you are very careful to only read the property if you actually use the data in the property.

ifergus replied on Thursday, May 29, 2008

Thanks Rocky, but I'm not binding it to anything. In fact, I created a very simple test application and I put a breakpoint on the getter. The getter was never triggered.

RockfordLhotka replied on Thursday, May 29, 2008

Let's take this one step at a time then.

You have NO CODE in the root DP_Fetch() to load the child object?
The only place in your app where you call LoadProperty() or SetProperty() to set the child field is in the property get block of the root object?
You do not have a private backing field for the child property (you are allowing FieldManager to take care of the value)?
You have a DP_Fetch() in the child object to load the child, and an internal/Friend factory on the child class that calls DataPortal.Fetch()?
The only place in all your code that calls that child factory method is the LoadProperty() call in the root object's property get?

If this is all true, then the only way for the child property to end up with a valid value is in that one line of code in the property get. That's the only place the factory is called, which is the only place that can cause the child to load with data.

ifergus replied on Thursday, May 29, 2008

I believe so, but here is the source. It's pretty simple:

using System;
using System.Collections.Generic;
using Csla;

using System.Configuration;
using Microsoft.Practices.EnterpriseLibrary.Data;
using Microsoft.Practices.EnterpriseLibrary.Data.Sql;
using System.Data.Common;
using System.Data;

namespace ParentChild
{
    public class Parent : BusinessBase<Parent>
    {
        public static PropertyInfo<int> IdProperty =
            RegisterProperty<int>(new PropertyInfo<int>("Id"));
        public int Id
        {
            get { return GetProperty<int>(IdProperty); }
            set { SetProperty<int>(IdProperty, value); }
        }

        public static PropertyInfo<string> NameProperty =
            RegisterProperty<string>(new PropertyInfo<string>("Name"));
        public string Name
        {
            get { return GetProperty<string>(NameProperty); }
            set { SetProperty<string>(NameProperty, value); }
        }

        public static PropertyInfo<Child> ChildItemProperty =
            RegisterProperty<Child>(new PropertyInfo<Child>("ChildItem"));
        public Child ChildItem
        {
            get
            {
                if (!FieldManager.FieldExists(ChildItemProperty))
                {
                    LoadProperty<Child>(ChildItemProperty, Child.Get(Id));
                }

                return GetProperty<Child>(ChildItemProperty);
            }
            set { SetProperty<Child>(ChildItemProperty, value); }
        }

        public static Parent Get(int Id)
        {
            return DataPortal.Fetch<Parent>(new ById(Id));
        }

        private void DataPortal_Fetch(ById criteria)
        {
            SqlDatabase db = new SqlDatabase(ConfigurationManager.ConnectionStrings["Local"].ConnectionString);
            DbCommand cmd = db.GetStoredProcCommand("GetParentById");

db.AddInParameter(cmd, "id", System.Data.DbType.Int32, criteria.Id);

            using (IDataReader reader = db.ExecuteReader(cmd))
            {
                reader.Read();

                LoadProperty<int>(IdProperty, Convert.ToInt32(reader["Id"]));
                LoadProperty<string>(NameProperty, reader["Name"].ToString());
            }
        }
        [Serializable()]
        private class ById
        {
            private int _id;

            public int Id
            {
                get
                {
                    return _id;
                }
            }
            public ById(int id)
            {
                _id = id;
            }
        }
    }
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Csla;
using Microsoft.Practices.EnterpriseLibrary.Data.Sql;
using System.Data.Common;
using System.Data;
using System.Configuration;

namespace ParentChild
{
    public class Child : BusinessBase<Child>
    {
        public static PropertyInfo<int> IdProperty =
            RegisterProperty<int>(new PropertyInfo<int>("Id"));
        public int Id
        {
            get { return GetProperty<int>(IdProperty); }
            set { SetProperty<int>(IdProperty, value); }
        }

        public static Child Get(int id)
        {
            return DataPortal.Fetch<Child>(new ById(id));
        }

db.AddInParameter(cmd, "id", System.Data.DbType.Int32, criteria.Id);

            using (IDataReader reader = db.ExecuteReader(cmd))
            {
                reader.Read();

                LoadProperty<int>(IdProperty, Convert.ToInt32(reader["Id"]));
                LoadProperty<string>(NameProperty, reader["Name"].ToString());
            }
        }

        [Serializable()]
        private class ById
        {
            private int _id;

RockfordLhotka replied on Thursday, May 29, 2008

One thing - a child property should never have a set block, only a get block. But I don't see how that would be your problem.

So what I'd do is put a breakpoint in your child object's Get() method and look at the stack trace to see how you got there. Very clearly SOME code is calling that method when you don't expect it :)

ifergus replied on Friday, May 30, 2008

Rocky, I don't think that Lazy Load works.

Calling a simple Get on the Parent results in the child being loaded. I could not get the applicaation to break when calling the Child's Get method. I do know that immediately after excuting the line:

result = methodHandle.DynamicMethod(obj, inParams);

in MehtodCaller.cs, both parent and child were set.

Csla.dll!Csla.Reflection.MethodCaller.CallMethod(object obj = {ParentChild.Parent}, Csla.Reflection.DynamicMethodHandle methodHandle = {Csla.Reflection.DynamicMethodHandle}, object[] parameters = {object[1]}) Line 221 + 0x1c bytes C#

Csla.dll!Csla.Reflection.MethodCaller.CallMethod(object obj = {ParentChild.Parent}, string method = "DataPortal_Fetch", object[] parameters = {object[1]}) Line 149 + 0xe bytes C#

Csla.dll!Csla.Reflection.LateBoundObject.CallMethod(string method = "DataPortal_Fetch", object[] parameters = {object[1]}) Line 86 + 0x17 bytes C#

Csla.dll!Csla.Server.SimpleDataPortal.Fetch(System.Type objectType = {Name = "Parent" FullName = "ParentChild.Parent"}, object criteria = {ParentChild.Parent.ById}, Csla.Server.DataPortalContext context = {Csla.Server.DataPortalContext}) Line 126 + 0x33 bytes C#

Csla.dll!Csla.Server.DataPortal.Fetch(System.Type objectType = {Name = "Parent" FullName = "ParentChild.Parent"}, object criteria = {ParentChild.Parent.ById}, Csla.Server.DataPortalContext context = {Csla.Server.DataPortalContext}) Line 120 + 0x12 bytes C#

Csla.dll!Csla.DataPortalClient.LocalProxy.Fetch(System.Type objectType = {Name = "Parent" FullName = "ParentChild.Parent"}, object criteria = {ParentChild.Parent.ById}, Csla.Server.DataPortalContext context = {Csla.Server.DataPortalContext}) Line 42 + 0x15 bytes C#

Csla.dll!Csla.DataPortal.Fetch(System.Type objectType = {Name = "Parent" FullName = "ParentChild.Parent"}, object criteria = {ParentChild.Parent.ById}) Line 219 + 0x12 bytes C#

Csla.dll!Csla.DataPortal.Fetch<ParentChild.Parent>(object criteria = {ParentChild.Parent.ById}) Line 165 + 0x34 bytes C#

ParentChild.dll!ParentChild.Parent.Get(int Id = 1) Line 50 + 0x23 bytes C#

ParentChildTest.dll!ParentChildTest.UnitTest1.TestMethod2() Line 27 + 0xb bytes C#

RockfordLhotka replied on Friday, May 30, 2008

I just created a test (though I already have other tests too) to firmly establish that a child isn’t created unless some code calls the child’s factory method. That statement is a truism of course J

Seriously though, lazy loading works fine. You absolutely have some code that is calling the child’s factory method when you don’t expect it. The easiest way to find the issue is to put a breakpoint in the child factory and then look at the stack trace to see who called it.

Here’s my test code:

var p = AParent.GetParent();

Display.AppendText(string.Format("{0}: {1}", "parent data", p.Data));