Try Catch in Repository

Question

None of the examples I have looked at for Repository Patterns include any kind of error handling. Why is this? Say for instance I have this:

public virtual TItem Insert<TItem>(TItem item) where TItem:class,new()
    {
        dbContext.Set<TItem>().Add(item);
        try
        {
            dbContext.SaveChanges();
        }
        catch (DbUpdateException)
        {

            return null;
        }

        return item;

    }

An instance where we violate a constraint. I catch the DbUpdateException... Where would this error handling live if not in the repository itself?

Answer 1

For the most part, a repository doesn't need to worry about handling exceptions. The classes that are consuming the repositories should handle that. In your example, why would want to return null if an insert error occurs? Isn't that less clear than just throwing an exception?

For example, let's say we want to insert a record through the repository and then print out the new ID. Assume that the insert is going to fail for any reason.

var myNewItem = myRepository.Insert(myItem);
Console.WriteLine("MyItem added with ID: {0}", myNewItem.ID);

Following the pattern in your question, you'd get a NullReference exception on the second line if the Insert fails. That's a little strange. It's more clear to see the DbUpdateException on the first line. It's also better to be able to count on Insert always either returning a valid instance or throwing an exception.