Question

I had a MockDataStore that returns a List<Task>. Then I would use the Aggregate extension method to query that list. So I was doing a LINQ-to-Objects query which does the job quiet nicely. Now that I’ve replaced my mock data store with a class that inherits the DbContext class, the same query does not work anymore because I cannot use a lambda expression that has a body since it cannot be converted to an expression tree. So is there a way to get around it and still have the aggregation done in SQL and avoid having to do it in-memory? Below is my code:

        //List<Task> tasks = MockDataStore.GetData()
        //    .Aggregate(new List<Task>(), (accumulator, treaty) => { accumulator.AddRange(treaty.Tasks); return accumulator; })
        //    .Where(x => x.AssignedTo.Equals(companyId) && x.StatusId == statusId).ToList();

        using (SCGREDbContext context = new SCGREDbContext())
        {
            List<Task> tasks = context.Treaties.Aggregate(new List<Task>(), (accumulator, treaty) => { accumulator.AddRange(treaty.Tasks); return accumulator; })
                                .Where(x => x.AssignedTo.Equals(companyId) && x.StatusId == statusId).ToList();
            return tasks;
        }

Answer 1

Why exactly are you using Aggregate()? I think your Aggregate() call is equivalent to this call to SelectMany():

context.Treaties.SelectMany(treaty => treaty.Tasks)