Question

I have a LINQ to Entities statement that joins two models on an AlphaGroupID, like this:

IEnumerable<ICD.ViewModels.HomeSearchViewModel> ICDList = (from a in ICDUnitOfWork.AlphaGroups.Find()
                                                                       join e in ICDUnitOfWork.Alphas.Find()
                                                                       on a.AlphaGroupID equals e.AlphaGroupID)

I need to join the two tables on AlphaGroupID, but I also need all of the ICDUnitOfWork.AlphaGroups regardless of whether or not they have a corresponding AlphaGroupID in ICDList. How can I accomplish this?

Answer 1

Use join into (it is same as GroupJoin):

var query = from a in ICDUnitOfWork.AlphaGroups.Find()
            join e in ICDUnitOfWork.Alphas.Find()
                   on a.AlphaGroupID equals e.AlphaGroupID into g
            select new { AlphaGroup = a, Alphas = g };

GroupJoin produces hierarchical result – for each item in outer sequence will be generated sequence of corresponding items in inner sequence (sequence could be empty).