向linq-to-sql表添加默认的where子句

Question

Is it possible to add a default where clause to every SQL statement generated by a Linq-to-SQL class?

I have a custom DataContext with a Customer class. The Customer class has a Deleted attribute, which is what I want to always be NULL whenever I query the table.

So for example, I could write:

List<Customer> customers = db.Customers.ToList<Customer>();

But really get:

List<Customer> customers = db.Customers.Where(o => o.Deleted == null).ToList<Customer>();

I want to maintain the "deleted" data in my DB, but will never need to see it in my .NET code. This sort of default would be handy, so I don't have to remember to add the filter to every query.

Answer 1

You can add a new property called ActiveCustomers that returns this:

public IQueryable<Customer> ActiveCustomers {
    get { return db.Customers.Where(e => e.Deleted == null); }
}

Any queries against that property can specify additional Where conditions and otherwise modify the results, but they will always be starting with customers who haven't been deleted. And due to LINQ's deferred execution this statement doesn't cause any additional queries to be executed.

If you need to ensure no one can access db.Customers you could try to hide it by doing something like this (may not work, I'd need to see your implementation):

public new IQueryable<Customer> Customers {
    get {
      throw new InvalidOperationException("Use property ActiveCustomers instead.");
    }
}

Answer 2

Instead of adding the table to your dbml designer, add a view that contains the default where clause, and just name the view Customer in your dbml.

To allow updates, inserts, and deletes, make sure you select the primary key columns in your DBML designer, and mark their Primary Key property as true.