CODEWITHSUNDEEP
c#linq
Shaul Behr
Shaul Behr

Reputation: 38003

How to make a compound "or" clause in Linq?

If you're adding "and" conditions to a Linq query, it's easy to do it like so:

var q = MyTable;
if (condition1)
  q = q.Where(t => t.Field1 == value1);
if (condition2)
  q = q.Where(t => t.Field2 > t.Field3);
// etc.

Is there any clever way of doing the same thing, when you want to add "or" conditions?

Upvotes: 8

Views: 4217

Answers (5)

John Leidegren
John Leidegren

Reputation: 60997

There is one way to do this that involves using expression trees. This way you build the Boolean expression yourself. It's pretty straight forward the tricky part though is that you need to rebase the parameters because otherwise it is going to refer the original lambda expression. See below for an example:

static void Main(string[] args)
{
    var source = new List<int> { 1, 2, 3 };

    var any = new List<Expression<Func<int, bool>>>();

    any.Add(x => x == 1);
    any.Add(x => x == 3);

    foreach (var item in source.AsQueryable().WhereDisjunction(any))
    {
        Console.WriteLine(item);
    }
}

class RewriteSingleParameterUsage : ExpressionVisitor
{
    public ParameterExpression Parameter { get; set; }

    protected override Expression VisitParameter(ParameterExpression node)
    {
        return Parameter;
    }
}

public static IQueryable<T> WhereDisjunction<T>(this IQueryable<T> source, IList<Expression<Func<T, bool>>> any)
{
    switch (any.Count)
    {
        case 0: return source;
        case 1: return source.Where(any[0]);
        default:
            var p = Expression.Parameter(any[0].Parameters[0].Type, any[0].Parameters[0].Name);
            var rw = new RewriteSingleParameterUsage { Parameter = p };
            var expr = rw.Visit(any[0].Body);
            for (int i = 1; i < any.Count; i++)
            {
                expr = Expression.Or(expr, rw.Visit(any[i].Body));
            }
            return source.Where(Expression.Lambda<Func<T, bool>>(expr, p));
    }
}

In the above example I'm being very harsh, I'm effectively replacing any parameter with this single new parameter that is being used to create the new expression. However, given the signature of this extension method it shouldn't really be possible to call this method with parameters such that it would cause an error. It is however going to be a problem if you involve more than one parameter.

Upvotes: 2

Eranga
Eranga

Reputation: 32437

This is the same answer I gave here

As Marc Gravell said it involves expression-tree combining.

This article shows you how to do that. It takes a bit of work to initially set it up. But its worth it.

Alternate solution is to use Predicate Builder. The article does not explain very well what is actually happening under-the-hood. But the above article explains it nicely

Upvotes: 1

Variant
Variant

Reputation: 17365

You can use a PredicateBuilder and use it to build an Or based expression:

 var predicate = PredicateBuilder.False<Product>();

 predicate = predicate.Or (t => t.Field1 == value1);
 predicate = predicate.Or (t => t.Field2 > t.Field3);

 q = q.Where (predicate);

You can read more about it here: http://www.albahari.com/nutshell/predicatebuilder.aspx

Replace the Product in PredicateBuilder.False<Product>() with your queried object.

Note that you start from a False predicate as you want to use Or. If You'd want an And predicate, Yuo should start from a True

Upvotes: 10

adrianm
adrianm

Reputation: 14726

var q = MyTable;
var conditions = new List<Func<T, bool>>();

 if (condition1)
     conditions.Add(t => ...);
 if (condition2)
     conditions.Add(t => ...);

 q.Where(x => conditions.Any(y => y(x)));

Upvotes: 2

Akram Shahda
Akram Shahda

Reputation: 14781

Use the following:

var q = MyTable;
q = q.Where(
     t => (condition1 && t.Field1 == value1) || (condition2 && t.Field2 > t.Field3));

Upvotes: 4

Related Questions