Attaching Existing Entity to New Entity (1-1 Relationship)

Consider an association in EF4 as:

Child 1----0..1 Parent

So, there's a non nullable foreign key in Parent for the Child.

I create a new Parent and assign an existing child. Unfortunately, this is a somewhat strange family as there are 300 parents, many sharing the same child.

When I try to save the 300 parent records, I encounter an UpdateException:

Entities in 'MyEntities.Parents' participate in the 'Child' relationship. 0 related 'Child' were found. 1 'Child' is expected.

Here's some code to illustrate:

// scope autosaves
using (new UnitOfWorkScope(true))
{
    var allParents= (from DataRow dataRow in this.dataTable.Rows
                     where dataRow != null
                     select CreateParent(dataRow)
                     into parents
                     where parents != null 
             开发者_StackOverflow        select parents).ToList();

    var parentFacade = new ParentFacade();

    foreach (var newParent in allParents)
    {
        parentFacade.Add(newParent);
    }
}

private static Parent CreateParent(DataRow dataRow)
{
    var parent = new Parent
    {
        SomeProperty = 'Moo',
        Child = GetChild(someValue)
    }

    return Parent;
}

private static Child GetChild(string someValue)
{
    return new ChildFacade().GetChild(someValue);
}

// Facade
public Child GetChild(string someValue)
{
    return (from c in this.ObjectContext.Children
            where c.SomeProperty == someValue
            select c).FirstOrDefault();
}

I can't figure out how to get around it. I want to save a new parent with a reference to an existing child.

Thanks,

Richard

many sharing the same child.

Your relation cannot be 1 - 0..1 but one to many where one parent can have many children. Your current relation says that Child has optional Parent and Parent must have a Child.