Databases
StackOverflow2013
Postsdbo
POReflection to call generic method with lambda expression parameter
Body
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POReflection to call generic method with lambda expression parameter
    text
    copied!<p>I'm looking for a way to call a generic method with a lambda expression that calls Contains in an array of items. </p> <p>In this case I'm using Entity Framework Where method, but the scenario could be applied in other IEnumerables.</p> <p>I need to call the last line of the above code through Reflection, so I can use any type and any property to pass to the Contains method.</p> <pre><code>var context = new TestEntities(); var items = new[] {100, 200, 400, 777}; //IN list (will be tested through Contains) var type = typeof(MyType); context.Set(type).Where(e =&gt; items.Contains(e.Id)); //**What is equivalent to this line using Reflection?** </code></pre> <p>In research, I've noticed that I should use GetMethod, MakeGenericType and Expression to achieve that, but I couldn't figure out how to do it. It would be very helpful to have this sample so I can understand how Reflection works with Lambda and Generic concepts.</p> <p>Basically the objective is to write a correct version of a function like this:</p> <pre><code>//Return all items from a IEnumerable(target) that has at least one matching Property(propertyName) //with its value contained in a IEnumerable(possibleValues) static IEnumerable GetFilteredList(IEnumerable target, string propertyName, IEnumerable searchValues) { return target.Where(t =&gt; searchValues.Contains(t.propertyName)); //Known the following: //1) This function intentionally can't be compiled //2) Where function can't be called directly from an untyped IEnumerable //3) t is not actually recognized as a Type, so I can't access its property //4) The property "propertyName" in t should be accessed via Linq.Expressions or Reflection //5) Contains function can't be called directly from an untyped IEnumerable } //Testing environment static void Main() { var listOfPerson = new List&lt;Person&gt; { new Person {Id = 3}, new Person {Id = 1}, new Person {Id = 5} }; var searchIds = new int[] { 1, 2, 3, 4 }; //Requirement: The function must not be generic like GetFilteredList&lt;Person&gt; or have the target parameter IEnumerable&lt;Person&gt; //because the I need to pass different IEnumerable types, not known in compile-time var searchResult = GetFilteredList(listOfPerson, "Id", searchIds); foreach (var person in searchResult) Console.Write(" Found {0}", ((Person) person).Id); //Should output Found 3 Found 1 } </code></pre> <p>I'm not sure if the other questions address this scenario, because I don't think I could clearly understand how Expressions work.</p> <p><strong>Update:</strong></p> <p>I can't use Generics because I only have the type and the property to be tested (in Contains) at run-time. In the first code sample, suppose "MyType" is not known at compile time. In the second code sample, the type could be passed as a parameter to the GetFilteredList function or could be get via Reflection (GetGenericArguments).</p> <p>Thanks,</p>
 

Querying!

 
Guidance
An individual column

Larger individual text columns get their own page to allow for proper reading.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload