Question

I have an abstract class:

public abstract class LMManager<ENTITY, ILM_ENTITY> where ENTITY : ILM_ENTITY, IActiveRecord, ICallOnCreated, new( )

ENTITY is some kind of DataObject, ILM_ENTITY, IActiveRecord, and ICallOnCreated are interfaces that the DataObject implements.

Typically, I subclass this guy with classes something like

public class JobManager : LMManager<Job, ILMJob>
public class JobViewManager : LMManager<vwJob, ILMJobView>

Now, I have a case where two of the sub-classes have some code in common, so I want to insert another layer in between, something like

public abstract class JobManagerBase : LMManager<ENTITY, ILM_ENTITY>

and then change the other two guys to

public class JobManager : JobManagerBase<Job, ILMJob>
public class JobViewManager : JobManagerBase<vwJob, ILMJobView>

In the definition of my JobManagerBase, I get four errors related to ENTITY:

1. Must be a non-abstract type with a public parameterless constructor
2. No boxing conversion or type parameter conversion from ENTITY to ICallOnCreated
3. No boxing conversion or type parameter conversion from ENTITY to IActiveRecord
4. No boxing conversion or type parameter conversion from ENTITY to ILM_ENTITY

Is it terribly obvious what I am missing?

Answer 1

Your JobManagerBase attempts to use LMManager with the parameters ENTITY and ILM_ENTITY.
Since these parameters do not meet your constraints, you get an error. (What if someone makes a JobManagerBase<int, string>?)

You need to add generic parameters and the same where clause to JobManagerBase to ensure that its parameters meet the constraints required for LMManager.