Linq one to many insert when many already exists

Question

So I'm new to linq so be warned what I'm doing may be completely stupid!

I've got a table of caseStudies and a table of Services with a many to many relasionship

the case studies already exist and I'm trying to insert a service whilst linking some case studies that already exist to it. I was presuming something like this would work?

 Service service = new Service()
        {
            CreateDate = DateTime.Now,
            CreatedBy = (from u in db.Users
                         where u.Id == userId
                         select u).Take(1).First(),
            Description = description,
            Title = title,
            CaseStudies = (from c in db.CaseStudies
                           where c.Name == caseStudy
                           select c),
            Icon = iconFile,
            FeatureImageGroupId = imgGroupId,
            UpdateDate = DateTime.Now,
            UpdatedBy = (from u in db.Users
                         where u.Id == userId
                         select u).Take(1).First()

        };

But This isn't correct as it complains about

Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Data.Objects.DataClasses.EntityCollection'

Can somebody please show me the correct way.

Thanks in advance

Answer 1

Yo have to add the query result to the case studies collection instead of trying to replace it.

var service = new Service { ... };                     

foreach (var caseStudy in db.CaseStudies.Where(s => s.Name == caseStudyName)
{
    service.CaseStudies.Add(caseStudy);
}

You can wrap this in an extension method and get a nice syntax.

public static class ExtensionMethods
{
    public static void AddRange<T>(this EntityCollection<T> entityCollection,
                                        IEnumerable<T> entities)
    {
        // Add sanity checks here.
        foreach (T entity in entities)
        {
            entityCollection.Add(entity);
        }
    }
}

And now you get the following.

var service = new Service { ... };                     

service.CaseStudies.AddRange(db.CaseStudies.Where(s => s.Name == caseStudyName));