Find the Any method on an array of strings

c# expression-trees linq

Question

Given

string[] stringArray = { "test1", "test2", "test3" };

then this returns true:

bool doesContain = stringArray.Any(s => "testa test2 testc".Contains(s));

My ultimate goal is to make a linq expression tree out of this. The question is how do I get the method info of "Any"? The following doesn't work because it returns null.

MethodInfo info = typeof(string[]).GetMethod("Any", BindingFlags.Static | BindingFlags.Public);

Further explanation:

I am creating search functionality. I use EF and so far using linq expression trees works to create a dynamic lambda expression tree. In this case I have an array of strings from which any string should occur in a description field. The working lambda expression that goes into the Where clause is:

c => stringArray.Any(s => c.Description.Contains(s));

So, to make the body of the lambda expression I need a call to "Any".

Final code:

Thanks to I4V's answer, creating this part of the expression tree now looks like this (and works):

//stringArray.Any(s => c.Description.Contains(s));
if (!String.IsNullOrEmpty(example.Description))
{
    string[] stringArray = example.Description.Split(' '); //split on spaces
    ParameterExpression stringExpression = Expression.Parameter(typeof(string), "s");
    Expression[] argumentArray = new Expression[] { stringExpression };

    Expression containsExpression = Expression.Call(
        Expression.Property(parameterExpression, "Description"),
        typeof(string).GetMethod("Contains"),
        argumentArray);

    Expression lambda = Expression.Lambda(containsExpression, stringExpression);

    Expression descriptionExpression = Expression.Call(
        null,
        typeof(Enumerable)
            .GetMethods()
            .Where(m => m.Name == "Any")
            .First(m => m.GetParameters().Count() == 2)
            .MakeGenericMethod(typeof(string)),
        Expression.Constant(stringArray),
        lambda);}

And then descriptionExpression goes into a larger lambda expression tree.

1
4
5/7/2013 6:02:01 PM

Accepted Answer

Maybe something like this?

var mi = typeof(Enumerable)
            .GetMethods()
            .Where(m => m.Name == "Any")
            .First(m => m.GetParameters().Count() == 2)
            .MakeGenericMethod(typeof(string));

And you can invoke it as:

var result = mi.Invoke(null, new object[] { new string[] { "a", "b" }, 
                                           (Func<string, bool>)(x => x == "a") });
1
5/7/2013 4:01:55 PM

Popular Answer

You can also do

// You cannot assign method group to an implicitly-typed local variable,
// but since you know you want to operate on strings, you can fill that in here:
Func<IEnumerable<string>, Func<string,bool>, bool> mi = Enumerable.Any;

mi.Invoke(new string[] { "a", "b" }, (Func<string,bool>)(x=>x=="a"))

And if you're working with Linq to Entities, you might want the IQueryable overload:

Func<IQueryable<string>, Expression<Func<string,bool>>, bool> mi = Queryable.Any;

mi.Invoke(new string[] { "a", "b" }.AsQueryable(), (Expression<Func<string,bool>>)(x=>x=="b"));


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