Question

I have implemented in the Add() method of my generic EF repository a check whether the row I’m going to insert already exists in the table, if it does, update it with the currently available info.

private List<T> _previousEntries;

//Try and find one with same PK in the temporary tables...
var previousRow = _previousEntries.Single(n => (int)n.GetType().GetProperty(_PKName).GetValue(n, null) == entPKValue);

//If we did find one...
if (previousRow != null)
{
   //Update the row...
   return;
}

//Add it...

So I know, I’m using reflection, which is slow but I have not found another way since different entities have different SQL PK names.

But I’m not sure that reflection is the biggest issue here, sometimes, _previousEntries will hold up to 800,000 items.

_previousEntries has its items assigned to it in the class constructor of the repository class. _PKName is also assigned a value in the class constructor depending on the type of T.

If I just set a breakpoint on the Single() statement, it can be processing for 2-3 seconds for sure so I don’t know how I could determine what is the bottleneck here: reflection or Single() on 800,000 items… It sure goes way faster on a 5,000 items list.

Any opinions ? Is there anything I can do to optimize my List ?

Answer 1

Provide a primary key accessor as a delegate

public class Repository<T>
{
    private Funct<T,int> _getPK;
    private Dictionary<int,T> _previousEntries;

    public Repository(Funct<T,int> getPK)
    {
        _getPK = getPK;
        _previousEntries = new Dictionary<int,T>();
    }

    public void Add(T item) {
        ...
        int pk = _getPK(item);
        T previousEntry;
        if (_previousEntries.TryGetValue(pk, out previousEntry) {
            // Update
        } else {
            // Add
            _previousEntries.Add(pk, item);
        }
    }
}

You would create a repositiory like this

var clientRepository = new Repositiory<Client>(c => c.ClientID);