LINQ to SQL is a very easy to use and very powerful tool for many things when dealing with SQL. But the time has come that I need to wrap it all up and use an iRepository pattern. I’ve Googled for the IRepository and found a few useful references but none that will complete my picture. How ever I did get some good ideas when looking around othe rimplementation of the IRepository pattern that others had implmented.
So why whould I use the iRepository when Linq to Sql and so good?
There are a few time, and this keeps happening that when you come to save an object you forget to use the SubmitChanges(), and what happens if there is a conflict. You can handle conflicts in Linq to Sql but you need to add extra code for each time you SubmitChanges(). The iRepository I am going to use will wrap all this up and sort it out for us in to one place. There are a number of reasons, but mainly the iRepository will provide a layer that I can use to hold all these methods in one place.
First the pattern will use Generics. So this means that you can passing in any Linq to Sql object and it will perform a task.
So here is the Interface I’ll be using:
public interface IRepository<T> where T : class
{
/// <summary>
/// Return all instances of type T.
/// </summary>
/// <returns></returns>
IEnumerable<T> All();
/// <summary>
/// Return all instances of type T that match the expression exp.
/// </summary>
/// <param name="exp"></param>
/// <returns></returns>
IEnumerable<T> FindAll(Func<T, bool> exp);
/// <summary>Returns the single entity matching the expression. Throws an exception if there is not exactly one such entity.</summary>
/// <param name="exp"></param><returns></returns>
T Single(Func<T, bool> exp);
/// <summary>Returns the first element satisfying the condition.</summary>
/// <param name="exp"></param><returns></returns>
T First(Func<T, bool> exp);
/// <summary>
/// Mark an entity to be deleted when the context is saved.
/// </summary>
/// <param name="entity"></param>
void MarkForDeletion(T entity);
/// <summary>
/// Create a new instance of type T.
/// </summary>
/// <returns></returns>
T CreateInstance();
/// <summary>Persist the data context.</summary>
void SaveAll();
long Count(Expression<Func<T, bool>> criteria);
void Save(T entity);
}
So that is the easy part, next is the concreate implementation of the interface
public class Repository<T> : IRepository<T>
where T : class
{
protected DataContext DataContext;
/// <summary>
/// Return all instances of type T.
/// </summary>
/// <returns></returns>
public IEnumerable<T> All()
{
return GetTable;
}
/// <summary>
/// Return all instances of type T that match the expression exp.
/// </summary>
/// <param name="exp"></param>
/// <returns></returns>
public IEnumerable<T> FindAll(Func<T, bool> exp)
{
return GetTable.Where(exp);
}
/// <summary>See _vertexRepository.</summary>
/// <param name="exp"></param><returns></returns>
public T Single(Func<T, bool> exp)
{
return GetTable.SingleOrDefault(exp);
}
/// <summary>See _vertexRepository.</summary>
/// <param name="exp"></param><returns></returns>
public T First(Func<T, bool> exp)
{
return GetTable.First(exp);
}
/// <summary>See _vertexRepository.</summary>
/// <param name="entity"></param>
public virtual void MarkForDeletion(T entity)
{
DataContext.GetTable<T>().DeleteOnSubmit(entity);
}
/// <summary>
/// Create a new instance of type T.
/// </summary>
/// <returns></returns>
public virtual T CreateInstance()
{
var entity = Activator.CreateInstance<T>();
GetTable.InsertOnSubmit(entity);
return entity;
}
/// <summary>See _vertexRepository.</summary>
public void SaveAll()
{
DataContext.SubmitChanges();
}
public long Count(Expression<Func<T, bool>> exp)
{
return GetTable.Where(exp).Count();
}
public void Save(T entity)
{
Save(new List<T> { entity });
return;
}
public void Save(IEnumerable<T> entities)
{
var table = DataContext.GetTable<T>();
foreach (var entity in entities)
{
var entity1 = entity;
var dbEntity = (from p in table
where p == entity1
select p).FirstOrDefault();
if (dbEntity == null)
table.InsertOnSubmit(entity);
try
{
// Save the changes.
DataContext.SubmitChanges();
}
// Detect concurrency conflicts.
catch (ChangeConflictException)
{
// Resolve conflicts.
DataContext.ChangeConflicts.ResolveAll(RefreshMode.KeepChanges);
}
}
}
public Repository(DataContext dataContext)
{
DataContext = dataContext;
}
#region Properties
private Table<T> GetTable
{
get { return DataContext.GetTable<T>(); }
}
#endregion
}
That is it, job done.
You’ll notice that in the Save method it handles quite a lot from inserting a new record, updating an exisiting record if one is found with the addition of an object copier to make life easier and then will save the changes to the database and if there happens to be any conflicts it deals with them.
The Save() will accept either single objects or and IEnumerable of an object making things easier and simpler.
I would love any feed back on what I have produced
To compliment the IRepository concreate class I’ve built a set of tests using MS Test that create and use a test database:
