Linq to SQL collections do not populate.

Question

I have a Linq to SQL class.

There is a one to many relationship in my database.

The relationship maps correctly in the designer, and an EntitySet<> property is created in the designer.

When I run the code, the EntitySet<> does not populate with any data, even though there are associated records, they do not populate into the EntitySet<>

Am I missing some property or setting? Do I have to write the query myself? I feel like I'm missing something obvious.

Here is the Designer code:

[Association(Name = "Bar_Foo", Storage = "_Foo", ThisKey = "ID", OtherKey = "BarID")]
[DataMember(Order = 15, EmitDefaultValue = false)]
public EntitySet<Foo> Foos
{
    get
    {
        if ((this.serializing && (this._Foo.HasLoadedOrAssignedValues == false)))
        {
            return null;
        }
        return this._Foo;
    }
    set
    {
        this._Foo.Assign(value);
    }
}

This is the code where I am trying to access the EntitySet<>:

    partial void OnCreated()
    {
        foreach (Foo foo in Foos)
        {
            foo.DoSomething();
        }
    }

More information about my situation:

So, from above I have a class Bar with a collection of Foo. What I am trying to do is pass Bar to a UI via a WCF service. Following is my primary service call:

public class TheService : ITheService
{
    public List<Bar> GetBars()
    {
        try
        {
            using (var db = new BarDataContext())
            {
                List<Bar> Bars = new List<Bar>();

                Bars = (from B in db.Bars
                            select B).ToList();

                return Bars;
            }
        }
        catch (Exception ex)
        {
            throw new FaultException(ex.Message + " Something in GetBars() Stack Trace: " + ex.StackTrace);
        }
    }
}

Currently, when the service returns the Bars the Foos inside each Bar is null.

If I create a property in Bar that looks at Foos, I get a null reference exception.

I try to run a query in the OnCreated method to fill Foos, the ID of the current Bar is 0.

Updated Query that still doesn't work:

                using (var ctx = new BarDataContext())
            {
                List<Bar> Bars= new List<Bar>();

                Bars= (from B in ctx.Bars
                             select B).ToList();

                foreach (Bar bar in Bars)
                {
                    bar.Foos= (from B in ctx.Bars
                               where B.ID == bar.ID
                               select B.Foos).SingleOrDefault();
                }

                return Bars;
            }

This code generates a null reference exception when I try to query Foos from Bar.

EDIT:

The code above magically stopped throwing null reference exceptions, dunno why. I find it interesting that you don't even need to set bar.Foos in the above query, you can put the Foos query into a variable that never gets used and it will fill in the Bar.Foos property, just because you looked at Foos. Reminds me of schrodinger's cat.

Answer 1

The OnCreated event applies to a single record object, not to the entire EntitySet. It's used primarily for setting default values for properties.

If you wish to retrieve a result set, you need to use a query to do so. For example:

var result = Foos.Where(a => a.ID == 7).Single();

The non-lambda equivalent would be:

var result = from a in Foos
             where (a => a.ID == 7)
             select a;

Edit

You can't use the OnCreated event to fill the Foos property in Bar, for the reason stated above. As a matter of fact, you don't have to manually fill the Foos property at all. If you have properly defined the foreign key relationship in your database and you have used the model designer to create the DataContext (*.dbml), the Foos property should already be filled when you retrieve Bar. You just need to access the Foos property from the Bar class:

var result = from a in DataContext.Bar
             where (a => a.ID == 7)
             select a.Foos;

This query will retrieve the collection of Foos associated with Bar #7.