Question

I have a linq to sql database. Very simplified we have 3 tables, Projects and Users. There is a joining table called User_Projects which joins them together.

I already have a working method of getting IEnumberable<Project> for a given user.

from up in User_Projects select up.Project; 

Now I want to get the projects the user isn’t involved with. I figured the except method of IEnumerable would be pretty good here:

return db.Projects.Except(GetProjects()); 

That compiles, however I get a runtime error: ‘Local sequence cannot be used in LINQ to SQL implementation of query operators except the Contains() operator.’

Is there any way to get around this?

---

Update:

A few views but no answers :p

I have tried this:

        IEnumerable<Project> allProjects = db.Projects;         IEnumerable<Project> userProjects = GetProjects();         return allProjects.Except(GetProjects()); 

I know it’s essentially the same as the original statement – but now i dont get a runtime error. Unfortunately, it doesn’t really do the except part and just returns all the projects, for some reason

Answer 1

Linq to Sql doesn’t understand how to work with an arbitrary in-memory sequence of objects. You need to express this in relational terms, which works on IDs:

var userProjectIds =     from project in GetProjects()     select project.ProjectId;  var nonUserProjects =     from project in db.Projects     where !userProjectIds.Contains(project.ProjectId)     select project;