How can I get the name of an ICollection<> property from a reference to the contained type?

Question

I have type references A and B but I want the name of the ICollection<A> which is a property of B. How can I get the collection name "BunchOfX" if I only have the two types?

public class X
{
}

public class Y
{
   public virtual ICollection<X> BunchOfX { get; set; }
}

I need something that can give me the property name "BunchOfX" when all I have is the type references A and B. Let's say A will reference the type that the ICollection<> holds, and B will reference the type the ICollection<> is defined on.

The Real Code

var entityType = Type.GetType(nameSpace + "." + entityTypeName);
var foreignType = Type.GetType(nameSpace + "." + foreignTypeName);
var names = foreignType.GetProperties()
    .Where(p => typeof(ICollection<entityType>).IsAssignableFrom(p.PropertyType))
    .Select(p => p.Name);
var foreignCollectionName = names.FirstOrDefault();

entityType gives "type or namespace unknown" when it is in the <>

Solution based on Jon and Ani's replies

var foreignCollectionName = foreignType.GetProperties()
    .Where(p => typeof(ICollection<>)
        .MakeGenericType(entityType)
        .IsAssignableFrom(p.PropertyType))
    .Select(p => p.Name).FirstOrDefault();

You'll most likely have to do it through reflection, or are you asking for specific code to find it? — Roman, Sep 04 '11 at 17:17
Are you saying that you want to call `Method(b.BunchOfA)` and be able to have `Method` know that it was passed in a property called `BunchOfA`? — Gabe, Sep 04 '11 at 17:17
@R0MANARMY I figured reflection, but I am a total beginner with .NET - specific code would be ideal. If it is very complicated then being pointed in the right direction would also be helpful. Thanks for your reply! — Benjamin, Sep 04 '11 at 17:19
possible duplicate of [workarounds for nameof() operator in C#: typesafe databinding](http://stackoverflow.com/questions/301809/workarounds-for-nameof-operator-in-c-typesafe-databinding) — Gabe, Sep 04 '11 at 17:19
@Gabe I'm not sure what you mean. But I think I asked the question the wrong way so I edited it. Thanks for your reply! — Benjamin, Sep 04 '11 at 18:05

score 4 · Answer 1 · answered Sep 04 '11 at 17:17

4

You'd need to look through the properties with reflection. The easiest way to do this is using LINQ:

var names = typeOfB.GetProperties()
                   .Where(p => p.PropertyType == typeof(desiredPropertyType))
                   .Select(p => p.Name);

answered Sep 04 '11 at 17:17

Jon Skeet

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The PropertyType of the PropertyInfo ICollection is the type 'A' ? Not just some collection type? Am I misunderstanding? It seems too easy. Thanks! – Benjamin Sep 04 '11 at 17:29
@Benjamin: No, the property type will be `ICollection` - that's what it's declared as. The type of the *value* returned from the property would be some concrete implementation, but the type of the property itself is `ICollection `. – Jon Skeet Sep 04 '11 at 17:33
Thanks, that makes sense. I think I botched this question though. I will only have run-time references to the two types. I will not have the type of the collection, only a reference to the type the collection property is designed to hold. I will have a reference to the type the collection is ON, and a reference to the type the collection can "collect". I didn't know how to ask this better. Does that make sense? Thanks for you help. – Benjamin Sep 04 '11 at 17:55
@Benjamin: Then I think your predicate in the `Where` clause should be: `p => typeof(ICollection).IsAssignableFrom(p.propertyType)` or similar. Or maybe `IEnumerable `? – Ani Sep 04 '11 at 18:05
Interesting, I will try it out. – Benjamin Sep 04 '11 at 18:08
@Benjamin: A reference to the type itself, or a reference to an instance of the type? It would *really* help if you'd give a short but complete example... – Jon Skeet Sep 04 '11 at 18:14
@Ani I get the error "The type or namespace name 'A' could not be found (are you missing a using directive or an assembly reference?)" - A is from Type.GetType(string) and debugs ok but as soon as I put it in between the <> in the ICollection<> then it is not recognized. – Benjamin Sep 04 '11 at 18:15
@Benjamin: It's far too unclear *exactly* what you've got, because you haven't shown us the code. Give us a complete example and it'll be easy to work out. – Jon Skeet Sep 04 '11 at 18:16
@Jon I pasted in my actual code above. I can give more if it is needed. I can never figure out what is helpful to provide with my questions so thanks for telling me. – Benjamin Sep 04 '11 at 18:23
1

@Benjamin: Looking at your update, looks like you want to replace the `typeof(..)` bit with `typeof(ICollection<>).MakeGenericType(entityType).IsAssignableFrom(p.propertyType)`. Goodness knows why you are playing around with so many strings though... – Ani Sep 04 '11 at 18:24
@Ani it works! Thank you to both of you. I will try to clean up the original post. If you have any advice regarding "so many strings" I certainly welcome it. My background is lame QBASIC screensavers, this is my first .NET project. Thanks again. – Benjamin Sep 04 '11 at 18:44

How can I get the name of an ICollection<> property from a reference to the contained type?

1 Answers1