Question

I have many methods like this:

    public IEnumerable<Director> GetAllDirectors()
    {
        using (var dbContext = new BodModelContainer())
        {
            return dbContext.Members.OfType<Director>().ToList();
        }
    }

..or this..

    public Member GetMemberById(int memberId)
    {
        using(var dbContext = new BodModelContainer())
        {
            return dbContext.Members.Find(new[] {memberId});
        }
    }

or that:

    public SomeType GetOrDoSomethingWithDbBySomethingElse(T1 t1var, T2, T2 var, ...)
    {
        using(var dbContext = new BodModelContainer())
        {
            return dbContext.SomeType.DoSomething();
        }
    }

So I wanna reorganize all of these methods something like:

    // create db context here
    public void InDb(Func<BodModelContainer, out SomeGenericType???> workingWithDb)
    {
         using(var dbContext = new BodModelContainer())
         {
             workingWithDb(dbContext);
         }
    }

    // using it like
    public Member GetMemberById(int memberId)
    {
            InDb((dbContext) => 
            { 
                    return dbContext.Members.Find(new[] { memberId }); 
            });
    }

Question: How to make such generic InDb method, what is SomeGenericType???

Answer 1

The actual problem it looks like you’re describing is the fact that you can’t figure out how to set the return type of the Func<>. To be able to make this generic you’ll need to make InDb require a generic type as well.

public TRet InDb<TRet>(Func<BodModelContainer, TRet> workingWithDb) {
  TRet ret = default(TRet);
  using (var dbContext = new BodModelContainer()) {
    ret = workingWithDb(dbContext);
  }
  return ret;
}

public Member GetMemberById(int memberId) {
  return InDb(dbContext => { return dbContext.Members.Find(new[] { memberId }); });
}

Should work (all the code here is untested), or using anonymous methods you could have a local variable and make .Net do all the nasty work.

public void InDb(Action<BodModelContainer> workingWithDb) {
  using (var dbContext = new BodModelContainer()) {
    workingWithDb(dbContext);
  }
}

public Member GetMemberById(int memberId) {
  Member member;
  InDb(dbContext => { member = dbContext.Members.Find(new[] { memberId }); });
  return member;
}

Of course, this all being said, I don’t know if this level of redirection/abstraction is useful – you’re making it slightly more complicated with little perceptible gain (if any). Unless there is a lot of work setting up and tearing down the dbContext used in InDb I don’t think it is very helpful.