Question

Why the below code throws ‘… has some invalid arguments at’

    var qry = listFoo.Where(lambda);

How should i write my listFoo inorder to call the Where on it by passing the predicate delegate. My entire code follow below,

    List<Foo> listFoo = new List<Foo>();

    ParameterExpression foo = Expression.Parameter(typeof(Foo), "foo");
    MemberExpression bar = Expression.PropertyOrField(foo, "Bar");
    ConstantExpression abc = Expression.Constant("abc", typeof(string)); 
    BinaryExpression test = Expression.Equal(bar, abc);

    Expression<Func<Foo, bool>> lambda = Expression.Lambda<Func<Foo, bool>>(test, foo);

    var qry = listFoo.Where(lambda);

Answer 1

Because your list is not IQueryable. Why don’t you just do this?

var qry = listFoo.Where(foo => foo.Bar == "abc");

If you can’t do that, do this:

var qry = listFoo.Where(lambda.Compile()); //warning, slow performance