Question

So basically I have an application that works with just one user, but I’d like to make it multi-user. This would involve me logging a user in, and keeping the user ID in session, plus adding a user id column to my database tables. no biggy.

I’d like to change my dbml, or use it’s partial, so that any query I throw through it also gets

.WHERE(user=>user.id=MYPARAM) 

added to it, to return just records for the logged in user.

Is there a quick win to be had? A single place where I can specify this in the .dbml?

Answer 1

I would perhaps create a lambda expression dynamically.

The Where clause takes an object of type Expression>

You can then create an expression using the following.

Expression<Func<User,bool>> func = null; 

Then

ParameterExpression xParam = Expression.Parameter(typeof(User), 'u'); 

You would then create an expression for u.id = ‘test’ by using a binary expression.

BinaryExpression uidTest = Expression.Equal(Expression.Property(xParam, 'id'),                                                                Expression.Constant('test'); 

and then attaching it to the Expression as follows:

func = Expression.Lambda<Func<User, bool>>(uidTest, xParam) 

In effect this is building a lambda expression u=> u.id = ‘test’

The func object can then be used in the .Where as follows: .Where(func)

Obviously, you can dynamically build this to any criteria you need at any time in your application.