Question

I have a very simple set-up. Table “Node” has a nullable foreign key “ObjectId.” This is represented in my database model with a one-to-many association. Now, I want to run a query that gives me all Node-Objects with a particular object id. In straight SQL, this is very easy:

SELECT Node.*, Object.*
FROM Node INNER JOIN Object
    ON Node.ObjectId = Object.ObjectId
WHERE Node.ObjectId = @objectId

But now I want to do the same thing in LINQ to SQL:

private static Func<MyDataContext, string, IQueryable<DataNode>> _queryGet =
        CompiledQuery.Compile(
            (MyDataContext context, string objectId) =>
                (from node in context.DataNodes
                 where node.ObjectId == objectId
                 select node));

var loadOptions = new DataLoadOptions();
loadOptions.LoadWith<DataNode>(node => node.DataObject);
context.LoadOptions = loadOptions;

DataNode node = _queryGet.Invoke(context, objectId).FirstOrDefault();
...

The frustrating thing is that LINQ always generates a LEFT OUTER JOIN for this query and nothing I’ve tried makes difference.

On the face of it, this seems to make sense. The ObjectId foreign key is nullable, so some nodes won’t have an associated object. But in my query, I’m supplying an object id. I’m not interested in nodes without an associated object.

In this case, an INNER JOIN is the right thing to do, but how do I convince LINQ?

Answer 1

I did eventually find a good solution to this. The answer is to simply get LINQ to SQL out of the way. Like so:

using (MyDataContext context = CreateDataContext())
{
    // Set the load options for the query (these tell LINQ that the
    // DataNode object will have an associated DataObject object just
    // as before).
    context.LoadOptions = StaticLoadOptions;

    // Run a plain old SQL query on our context.  LINQ will use the
    // results to populate the node object (including its DataObject
    // property, thanks to the load options).
    DataNode node = context.ExecuteQuery<DataNode>(
        "SELECT * FROM Node INNER JOIN Object " +
        "ON Node.ObjectId = Object.ObjectId " +
        "WHERE ObjectId = @p0",
        objectId).FirstOrDefault();

    //...
}