CODEWITHSUNDEEP
c#dynamic
5SK5
5SK5

Reputation: 169

Dynamic Expression to query a list

I have a method that passes a field that belongs to type T, and then an operator like Contains or Equals or StartsWith

I have this code so far:

IQueryable<Review> queryable = this.rvCurReviewSet.AsQueryable<Review>();

var paramExp = Expression.Parameter(typeof(Review), "review");
var propExp = Expression.Property(paramExp, "ProductID");
MethodInfo method = typeof(string).GetMethod("Contains", new[] { typeof(string) });
var val = Expression.Constant(input, typeof(string));
var containsExp = Expression.Call(propExp, method, val);

Console.WriteLine(queryable.Provider.CreateQuery<Review>(containsExp).Count());

When I run this I get the error: Additional information: Argument expression is not valid

Basically, I want to see if a field in Review satisfies the criteria. So, for example I would find Review.ProductID contains "123" or Review.ProductID startsWith "123" and so on.

Upvotes: 1

Views: 359

Answers (1)

Rob
Rob

Reputation: 27357

You were nearly there - but you need to pass it a lambda expression..

var lam = Expression.Lambda<Func<Review, bool>>(containsExp, paramExp);
Console.WriteLine(queryable.Provider.CreateQuery<Review>(lam).Count());

What you had was a body expression, which operated on review, but didn't specify where the value for review comes from.

Upvotes: 2

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