CODEWITHSUNDEEP
entity-framework
MuriloKunze
MuriloKunze

Reputation: 15583

How to use 'Or' in Where clauses?

I need something like this: Select name from users where id = 1 or id = 2. I know I can do this:

_db.Users
.Where(u => u.Id == 1 || u.Id == 2);

But is there any alternative to this? Is there something like this:

_db.User
.Where(u => u.Id == 1)
.Or
.Where(u => u.Id == 2)

Upvotes: 0

Views: 150

Answers (3)

Alex M
Alex M

Reputation: 2548

I usually use next form to build dynamic linq with ORs and ANDs.

public class Linq
{
 public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expression1,
                                                        Expression<Func<T, bool>> expression2)
{
        if (expression1 == null) throw new ArgumentNullException("expression1", "Consider setting expression1 to Linq.True<T>() or Linq.False<T>()");
        var invokedExpr = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.OrElse(expression1.Body, invokedExpr), expression1.Parameters);
}


public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expression1,
                                                         Expression<Func<T, bool>> expression2)
    {
        if (expression1 == null) throw new ArgumentNullException("expression1", "Consider setting expression1 to Linq.True<T>() or Linq.False<T>()");
        var invokedExpr = Expression.Invoke(expression2, expression1.Parameters.Cast<Expression>());
        return Expression.Lambda<Func<T, bool>>
              (Expression.AndAlso(expression1.Body, invokedExpr), expression1.Parameters);
    }

public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }
}

And then use it in your code:

Expression<Func<User, bool>> searchExpression = Linq.False<User>();

searchExpression = Linq.Or<User>(searchExpression, b => b.Id==1);
searchExpression = Linq.Or<User>(searchExpression, b => b.Id==2);

Then you use this searchExpression as

_db.Users.Where(searchExpression);

With this form it is very easy to build dynamic queries, like:

Expression<Func<User, bool>> searchExpression = Linq.False<User>();
searchExpression = Linq.Or<User>(searchExpression, b => b.Id==1);
if (!String.IsNullOrEmpty(name))
    searchExpression = Linq.Or<User>(searchExpression, b => b.Name.StartsWith(name));
//combine with OR / AND as much as you need

It will generate only one query to the DB.

Upvotes: 2

Tiago Gouv&#234;a
Tiago Gouv&#234;a

Reputation: 16740

You just want:

_db.Users.Where(u => (u.Id == 1 || u.Id == 2));

Upvotes: 0

user743382
user743382

Reputation:

Not directly. Remember, _db.Users.Where(u => u.Id == 1) is the user whose id is 1. You cannot get the user with id 2 from that, because it isn't there.

You can use some other approach, such as

var user1 = _db.Users.Where(u => u.Id == 1);
var user2 = _db.Users.Where(u => u.Id == 2);
var users = user1.Union(user2);

or

var userids = new int[] { 1, 2 };
var users = _db.Users.Where(u => userids.Contains(u.Id));

though.

Upvotes: 2

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