Query Entity Framework for list of dynamic type

Question

When querying entity framework for all objects of a given type, you'd do something like this:

List<MyDesiredObjects> = _myContext.MyDesiredObjects.ToList();

But is there a way one can create a function to query EF to find all objects of a given type if the type is variable? I've created this function, which at least compiles:

private List<TEntity> GetFromEF<TEntity>() where TEntity : class
{
    MyDBEntities context = new UnityDBEntities(_entityConnection);

    IObjectContextAdapter adapter = (IObjectContextAdapter)context;
    System.Data.Objects.ObjectContext oContext = adapter.ObjectContext;

    return oContext.CreateObjectSet<TEntity>().ToList();
}

But I'm struggling to see how I can call it, never mind actually extract data from it. Using reflection, like this (ucm.MappingType is a Type):

MethodInfo method = typeof(BaseXmlReader).GetMethod("GetFromEF");
MethodInfo gMethod = method.MakeGenericMethod(  ucm.MappingType.GetType() );
var meh = gMethod.Invoke(null, null);

Fails with object reference not set to instance of object. And I've not even got to paging my list yet.

Any other way to approach this problem?

Where are you getting the exception? Is it when you are invoking the method or in GetFromEF? — Mike Norgate
– Mike Norgate, Commented Nov 18, 2013 at 15:10
It's on method.MakeGenericMethod - but I just spotted that's because method is null. — Bob Tway
– Bob Tway, Commented Nov 18, 2013 at 15:12
One way to call a generic method is like this: var list = GetFromEF<MyDesiredObjects>(); No need to get into reflection. msdn.microsoft.com/en-us/library/ms379564(v=vs.80).aspx — Colin
– Colin, Commented Nov 18, 2013 at 15:20
You will probably need to provide these binding flags to GetMethod to enable it to get your private method BindingFlags.NonPublic | BindingFlags.Instance — Mike Norgate
– Mike Norgate, Commented Nov 18, 2013 at 15:21
The first parameter of the invoke needs to be an instance of BaseXmlReader, you cannot invoke on a null instance — Mike Norgate
– Mike Norgate, Commented Nov 18, 2013 at 15:31

mayabelle · Accepted Answer · 2013-11-18 15:53:29Z

1

To address your issue of having a null MethodInfo method:

GetMethod will only search for public members. You can change your method to public, or include nonpublic methods like this:

MethodInfo method = typeof(BaseXmlReader)
                       .GetMethod("GetFromEF", 
                                  BindingFlags.Instance | BindingFlags.NonPublic);

Also, I'm assuming that your GetFromEF method is on a class called BaseXmlReader? If not, that needs to be replaced with the class name.

Then you can invoke like this:

BaseXmlReader instance = new BaseXmlReader();
MethodInfo method = typeof(BaseXmlReader)
                       .GetMethod("GetFromEF", 
                                  BindingFlags.Instance | BindingFlags.NonPublic);
MethodInfo gMethod = method.MakeGenericMethod(typeof(ucm.MappingType));
var result = gMethod.Invoke(instance, null);

or like this if being called from inside itself:

MethodInfo method = typeof(BaseXmlReader)
                       .GetMethod("GetFromEF", 
                                  BindingFlags.Instance | BindingFlags.NonPublic);
MethodInfo gMethod = method.MakeGenericMethod(typeof(ucm.MappingType));
var result = gMethod.Invoke(this, null);

edited Nov 18, 2013 at 15:53

answered Nov 18, 2013 at 15:32

mayabelle

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1 Comment

Bob Tway Over a year ago

It's actually being called from inside itself, so the Invoke is gMethod.Invoke(this, null) ... but the principal is the same. Thanks!

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