filter a linq query based on the results of another query's results

Question

I am wanting to filter a linq query

I have 2 linq statements

The 1st gets all the stores I want and the 2nd is where I filter information based on the results found in the 1st query.

var stores = ctx.Stores.Where(ps => ps.ParentStoreID == parent.ParentStoreID && ps.StoreID!=storeID);

var query = (from a in ctx.TransactionTable
          from b in ctx.MappingTable.Where(x => x.TransactionId== a.TransactionId).DefaultIfEmpty()
             where a.StoreID!=storeID
                 select new
                           {
                              Transactions = a,
                              Mapping = b
                           }).ToList();

How do I add another where clause into my 2nd query to only return results where a.StoreId is contained within the stores result?

Answer 1

Like this:

var stores = ctx.Stores.Where(ps => ps.ParentStoreID == parent.ParentStoreID && ps.StoreID!=storeID);

var query = (from a in ctx.TransactionTable
            from b in ctx.MappingTable.Where(x => x.TransactionId==a.TransactionId).DefaultIfEmpty()
            where a.StoreID!=storeID && stores.Select(s => s.StoreID).Contains(a.StoreID)
            select new
            {
                Transactions = a,
                Mapping = b
            }).ToList();

You can find more info here: Linq to Entities - SQL "IN" clause