Question

I have this method to get a generic repository out of a dictionary:

public readonly IDictionary<Type, IRepository> _repositories = new Dictionary<Type, IRepository>();

public IRepository GetRepository(Type type)
{
    if (this._repositories.ContainsKey(type)) {
        return this._repositories[type];
    }
    return null;
}

That works but I want it to work using generics so I tried:

public IRepository<T> GetRepository<T>() where T : class
{
    var typeParameterType = typeof(T);

     if (this._repositories.ContainsKey(typeParameterType)) {
         return this._repositories[typeParameterType];
     }
     return null;
}

But I get an error like ‘Cannot implicitly convert type IRepository to IRepository<T>. An explicit conversion exists (are you missing a cast?)

Anybody know how to resolve this?

Answer 1

As the error suggests, you’ll need to either change GetRepository‘s return type to the non-generic IRepository:

public IRepository GetRepository<T>() where T : class
{
    var typeParameterType = typeof(T);

    if (this._repositories.ContainsKey(typeParameterType)) 
        return this._repositories[typeParameterType];

    return null;
}

Or, simply cast the return of this._repositories to the generic type IRepository<T>:

public IRepository<T> GetRepository<T>() where T : class
{
    var typeParameterType = typeof(T);

    if (this._repositories.ContainsKey(typeParameterType)) 
        return this._repositories[typeParameterType] as IRepository<T>;

    return null;
}

Or possibly more appropriate:

public IRepository<T> GetRepository<T>() where T : class
{
    Repository<T> rep = null;

    this._repositories.TryGetValue(typeof(T), out rep);

    return rep;
}