Question

I have this aggregate root

CustomerGroup
int Id
string Name
Customer[] Customers

And this one

Customer
int Id
string Name

My model was built using EF 4. What i’d prefer would be (for sticking to the concept of aggregate root)

CustomerGroup
int Id
string Name
int[] Customers

How would you do this ?

A customer might be in many gorup (many to many relationship) but I only need the relationship in one way group -> customer. I don’t have any use case where I need customer -> group.

Answer 1

As you have a many-to-many association between Customer and CustomerGroup there also is a so called junction table, let’s say CustomerGroupCustomer, that has CustomerId and CustomerGroupId.

If this table only has these two fields EF can use it implicitly, which means that CustomerGroup can have a Customers collection where in the mapping you indicate that CustomerGroupCustomer is the junction table. Here is an example. You can, but don’t have to, map Customer.CustomerGroups. When working database-first, this implicit behaviour is the default.

However, since you’re interested in CustomerIds only you could decide to have a regular one-to-many association CustomerGroup.CustomerGroupCustomers. If you address this navigation property only one join is required and the query is pretty light. If you have a CustomerGroup instance you can do

group.CustomerGroupCustomers.Select(c => c.CustomerId)

and only the CustomerIds will be queried.

If you want you can get the Customers directly by doing

group.CustomerGroupCustomers.Select(c => c.Customer)