CODEWITHSUNDEEP
c#linq
Robert
Robert

Reputation: 1726

Remove entities from collection

I have 3 tables; Groups, Customers, and GroupCustomers. Groups can have many customers, hence the reason for the GroupCustomers table. In my C# WinForms program, I am trying to delete all the Customers for a specific Group using Linq. Here's my code that seems to work but it I think I am missing something to make this query a lot smaller/easier/faster to read & execute.

Context.Groups.Where(g => g.Id == group.Id)
                        .FirstOrDefault()
                        .Customers.ToList()
                        .ForEach(gc =>
                            {
                                Context.Groups.Where(g => g.Id == group.Id)
                                                            .FirstOrDefault()
                                                            .Customers.Remove(gc);
                            });
Context.SaveChanges();

group.Id is a variable that is passed into this method.

Upvotes: 1

Views: 82

Answers (2)

Jeff Mercado
Jeff Mercado

Reputation: 134841

Write a query to select all the items you wish to remove. You wish to remove all customers that are within a particular group. That would correspond to the GroupCustomers that was created to link the two. Select those, then remove them.

var toBeRemoved =
    from gc in Context.GroupCustomers
    where gc.GroupId == group.Id
    select gc;
foreach (var gc in toBeRemoved)
    Context.GroupCustomers.DeleteObject(gc);
Context.SaveChanges();

Otherwise, what you have is logically fine, but I would make a few adjustments. Select the group to remove customers from and remove the customers from the group. .ToList().ForEach() should never be used as a substitute for a regular call to foreach.

var removeFromGroup = Context.Groups.FirstOrDefault(g => g.Id == group.Id);
foreach (var c in removeFromGroup.Customers)
    removeFromGroup.Remove(c);
Context.SaveChanges();

Upvotes: 0

mazharenko
mazharenko

Reputation: 635

I think you're too stuck on LINQ. I'd write this:

 var group = Context.Groups.First(g => g.Id == group.Id); // if you're sure of existing
 foreach (var customer in group.Customers.ToList()) // ToList is required to avoid 'Collection was modified' exception, I think
      Context.Customers.Remove(customer);
 Context.SaveChanges();

Upvotes: 1

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