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Another "generic" question. Coming up with BaseRepository

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Category: DevForce
Forum Name: DevForce 2010
Forum Discription: For .NET 4.0
URL: http://www.ideablade.com/forum/forum_posts.asp?TID=3210
Printed Date: 13-May-2026 at 1:58pm


Topic: Another "generic" question. Coming up with BaseRepository
Posted By: katit
Subject: Another "generic" question. Coming up with BaseRepository
Date Posted: 11-Jan-2012 at 9:30pm
I'm finding that all my data repositories look alike and decided to try and make one base class with generics.
 
However, I'm struggling with following piece of code(see screenshot). How do I create entity instance of <T> in this GetNew() method?
 


Replies:
Posted By: katit
Date Posted: 12-Jan-2012 at 6:32am
Found solution.. Needed to do where T: Entity, new()
var Entity = new T(); //works

Posted By: smi-mark
Date Posted: 12-Jan-2012 at 8:33am
Rather than create a repository per entity type, you may want to create one per unit-of-work. Otherwise you are going to be creating a lot more work for your self than needed.

By unit of work, I mean a related set of entities. An example might be employees, the primary entity is Employee, but you also may have contacts, addresses, and other such related entities.

This is what I do:

public abstract class RepositoryBase<T> : IRepository
        where T : EntityManager
    {
    }

then I would create an IEmployeeRepository that might look like this:

public interface  IEmployeeRepository : IRepository
    {
        INotifyCompleted GetEmployee(Guid employeeId, Action<Employee> onSuccess, Action<Exception> onFail);
        INotifyCompleted GetEmployeeHistory(Guid employeeId, Action<IEnumerable<EmployeeHistory>> onSuccess, Action<Exception> onFail);
     }

    public class EmployeeRepository :RepositoryBase<MyEntities>, IEmployeeRepository
    {
        public INotifyCompleted GetEmployee(Guid employeeId, Action<Employee> onSuccess, Action<Exception> onFail)
        {

        }

        public INotifyCompleted GetEmployeeHistory(Guid employeeId, Action<IEnumerable<EmployeeHistory>> onSuccess, Action<Exception> onFail)
        {

        }
     }

DevForce Caliburn is a great framework to look at, I believe they have examples very similar to this.

Posted By: katit
Date Posted: 12-Jan-2012 at 8:43am
Actually, I am creating repository per unit of work as you suggest. Entity type in this case represents primary entity and I use "includes" to get other related entities that I need. Each repository takes care of maintaining (CRUD) whole MVVM for Silverlight's view.
 
Since you posted this sample, I was wondering why do I want to use INotifyCompleted? I find it easier to write code like below. When do I see benefit of using this interface? Simple Actions work well for me.
 

public void SaveAll(Action onSuccess = null, Action<Exception> onFail = null)

{

var op = this.EntityManager.SaveChangesAsync();

op.OnComplete(onSuccess, onFail);

}

 

 

 

Posted By: smi-mark
Date Posted: 12-Jan-2012 at 9:11am
One of the places I make use of the INotifyCompleted is with my Busy indicators. I might write some code like this:

Employee employee;
Busy.AddWatch();
Repository.GetEmployees(123, e => employee = e, ErrorHandler.HandleError)
                .WhenCompleted(args => Busy.RemoveWatch());

This way it's saying, no matter what the result, success or fail, I want to make sure I am executing a certain action.

Without this, you are forced to write code that looks like this:

Busy.AddWatch();
Repository.GetEmployees(123, e =>
{
   employee = e
   Busy.RemoveWatch();
},
(ex) =>
{
    ErrorHandler.HandleError(ex);
    Busy.RemoveWatch();
});

Posted By: katit
Date Posted: 12-Jan-2012 at 9:13am
Fair enough. Yes, I was writing BusyOff on error and success, so that will help me make this async code even better..


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