Question

I have Users->Orders tables (one to many) and would like to select all users which have specified Orders. I have tried Linq below but it fails with error. How to write such Linq query?

DataAccess.Instance.Users.Where(p => p.Orders.Where(o => o.ProductId == productId))

Answer 1

You should try:

DataAccess.Instance.Users.Where(p => p.Orders.Any(o => o.ProductId == productId))

Note that the second Where is changed to Any which returns a boolean value and satisfies the type of the expression tree expected by the first Where: Where needs a condition, not a set of values retrieved from elsewhere.