Question

I am implementing a FakeDataSet class by implementing IDbSet interface. As part of implementing this interface, I have to implement Find method. All my entity classes has an Guid type Id column. I am trying to implement Find method for this FakeDbSet class but having hard time to write it in a generic way. Below is my attempts for writing this method.

public class FakeDataSet<T> : IDbSet<T> where T: class, new()  
{  
  //  Other methods for implementing  IDbSet interface
  public T Find(params object[] keyValues)  
  {  
       var keyValue = (Guid)keyValues.FirstOrDefault();
       return this.SingleOrDefault(m => m.Id == keyValue);  // How can I write this
  }
}

Since it does not know about Id being of Guid type, I am getting compilation error on m.Id call.

‘T’ does not contain a definition for ‘Id’ and no extension method
‘Id’ accepting a first argument of type ‘T’ could be found (are you
missing a using directive or an assembly reference?)

Any ideas on how this could be accomplished?

Answer 1

Something like this to give you an idea:

public virtual T Find(params object[] keyValues)
{
    if (keyValues.Length != _keyProperties.Count)
        throw new ArgumentException("Incorrect number of keys passed to find method");

    IQueryable<T> keyQuery = this.AsQueryable<T>();

    for (int i = 0; i < keyValues.Length; i++)
    {
        var x = i; // nested linq

        keyQuery = keyQuery.
        Where(entity => _keyProperties[x].GetValue(entity, null).Equals(keyValues[x]));
    }

    return keyQuery.SingleOrDefault();
}

Source: Generic Repository: Fake IDbSet implementation update (Find Method & Identity key)