How to filter a query with the values from a list in ef core

I have a list that is the result of a db query. I need to be able to query another table but filter that query based on the first list. In a perfect world I would join these two tables but they are from different databases that reside on different servers and as far as I know the only way to do this is to link the servers which I'm not allowed to do.

I have already queried both tables and joined the results in a separate list, but the second query returns massive results when run wide-open and it bogs everything down. list1 is a list of Areas that references "SubAreas", which then references "Operations" which correlates to "OperationName" in list2.

I thought I could add a ".where" clause to list2 like this but it didn't work:

.Where(a => list1.Any(b => b.Subareas.Any(c => c.Operations.Any(d => d.Name == a.OperationName)))) Note: selectedArea!.Name is a form value the user must select before any of this happens. private async Task GetRecords( { var list1 = await dbcontext1.Areas .Where(a => a.Name == selectedArea!.Name) .Include(a => a.Subareas) .ThenInclude(a => a.Operations) .ToListAsync(); var list2 = await dbcontext2.ProdDetails .Where(a => !string.IsNullOrEmpty(a.OperationName)) .Select(a => new { Customer = a.Customer, Assembly = a.Assembly, AssemblyDescription = a.AssemblyDescription, AssemblyRevision = a.AssemblyRevision, WorkOrder = a.WorkOrder, Batch = a.Batch, BatchQuantity = a.BatchQuantity, Barcode = a.Barcode, LastWipTime = a.LastWipTime, InProcess = a.InProcess, OperationName = a.OperationName }) .ToListAsync(); //do more stuff not relevant to this question... }

Hopefully I have explained myself clearly enough.