Add RollbackUnlessCommitted

[DoubleDi]

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• Do only one thing
• No API-breaking changes
• New code/logic commented & tested

For significant changes like big bug fixes, new features, please open an issue to make an agreement on an implementation design/plan first before starting it.

What did this pull request do?

Hi @jinzhu ! Awesome refactoring with v2 going on.
Added RollbackUnlessCommitted func for transactions. Helps not to write a lot of rollback code on error checking!

Example

tx := db.Begin()
defer tx.RollbackUnlessCommitted()
if somerrhappened {
     // no need for rollback here
     return
}
if othererrhappened {
     // no need for rollback here
     return
}
tx.Commit()

also please keep in mind that you should write commiTTer with double T.

[jinzhu]

Hello,

Thank you for your PR.

It won't work after adding the RollbackUnlessCommitted method to TxCommiter as database/sql doesn't implement this method.

And I would suggest we don't add API like this but just using method Transaction like this http://gorm.io/docs/transactions.html#Transactions

Could you open another PR to fix the typo, thank you ;)

[DoubleDi]

Yes, didn't think of that. Thank you @jinzhu
I reviewed the changes and we actually don't need RollbackUnlessCommitted in TxCommitter, only need it in DB. So maybe this PR is still considerable?
Or maybe we can use you callbacks and put beside CommitOrRollback?

[jinzhu]

Have you checked out the Transaction method? I prefer to use it than adding a new API.

[DoubleDi]

Ok it's pretty handy too. Thanks