where to put the validate logic? In Service or Repository?

Question

I have some logic like this, before save the stock into the db, i will check whether there is stock has the same stock code in the database. My question is where should I put the logic, in the service layer or repository layer. here is the sample code:
option 1: put in the service layer, i put the IsAccountAlreadyExists Method in the service layer

public override void Save(AccountInfo accountInfo)
{
    using (var scope = new TransactionScope())
    {
        if(this.IsAccountAlreadyExists(accountInfo))
        {
            throw new AccountAlreadyExistedException(
                "Account Code : " + accountInfo.AccountCode +
                " already existed.");
        }

        accountRepository.Save(accountInfo);
            scope.Complete();
    }
}

option 2: I will move the IsAccountAlreadyExists logic to the repository layer.

public override void Save(AccountInfo accountInfo)
{
    try
    {
        using (var scope = new TransactionScope())
        {
            accountRepository.Save(accountInfo);
            scope.Complete();
        }
    }
    catch(AccountAlreadyExistedException e)
    {
        ...
    }
}

what's your opinion?

Answer 1

I consider this to be three tiers (with an interface defined to connect each piece):

• Data Repository - only for storing and retrieving raw data. As little logic goes here as possible.
• Business Model - all the smarts goes here, including validation.
• Service (i.e. client access) - a very thin piece, just enough to provide a connection to the client.

This way, if you choose to store your data in some other fashion, the validation logic doesn't get lost with it.

Similarly, if you decide to provide a different form of client access, you do it without needing to replicate a bunch of logic.