CODEWITHSUNDEEP
c#expressioniqueryablepredicateicollectionview
Marc Canals Giraut
Marc Canals Giraut

Reputation: 354

Convert Predicate<T> to Expression<Func<T, bool>>

Is possible to convert a Predicate<T> to Expression<Func<T, bool>> in some way?

I would like to use the next IQueryable function using the filters of the my ICollectionView:

public static System.Linq.IQueryable<TSource> Where<TSource>(this System.Linq.IQueryable<TSource> source, System.Linq.Expressions.Expression<System.Func<TSource, bool>> predicate)

Thanks

Upvotes: 7

Views: 9076

Answers (3)

user3830154
user3830154

Reputation: 25

namespace ConsoleApplication1
{
    static class Extensions
    {
        public static Expression<Func<T, bool>> ToExpression<T>(this Predicate<T> p)
        {
            ParameterExpression p0 = Expression.Parameter(typeof(T));
            return Expression.Lambda<Func<T, bool>>(Expression.Call(p.Method, p0), 
                  new ParameterExpression[] { p0 });
        }
    }
}

Upvotes: 1

Steven
Steven

Reputation: 172835

In theory it is possible to convert a delegate 'back' to an expression, because you can request the emitted IL of a delegate, which gives you the information you need to transform it back.

However, it's for a reason that neither LINQ to SQL and Entity Framework do this. It is complex, fragile, and performance intensive to do so.

So the short answer is, you can't transform it to an expression.

Upvotes: 5

Jesse van Assen
Jesse van Assen

Reputation: 2290

Something like this?

Predicate<string> predicate = input => input.Length > 0;
Expression<Func<string, bool>> expression = (input) => predicate(input);

You can probably make an extension Where method for your ICollectionView which takes a predicate, converts it to an Expression like this, and then call the Where method provided by Linq.

public static IQueryable<T> Where(this IQueryable<T> source, Predicate<T> predicate)
{
    return source.Where(x => predicate(x));
}

Upvotes: 6

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