Add a single transaction rule

[GradedJestRisk]

:unicorn: Problem

Knex implements explicit transactions, but allow to mix

• a query in an explicit transaction
• a query in the default transaction

Such a code would not be implemented purposefully, and may end up exhausting the connection pool

//  Take a connection A from the pool
//  Initiate a transaction on connection A

knex.transaction((trx) => {

   //  Take a connection B from the pool
   //  Initiate a transaction on connection B

  // Bug here, the code should be trx.update()
  knex.update();

   //  Validate transaction in connection B 
   //  Release connection B to the pool

}) 
//  Validate transaction in connection A 
//  Release connection A to the pool

Such an issue has been raised in knex repo

:robot: Solution

Implement a rule that does not allow mixing transactions

:rainbow: Remarks

Such a behavior occurred in production in this repository yesterday, blocking hundred of thousand of users

FYI, the original fix is here

[AntonNiklasson]

Thanks for reporting this! I'm not sure static code analysis is the best approach to solving this, but perhaps we could take a stab at it. Are you open to work on this?

A good name for this rule might be no-mixed-transactions.

[GradedJestRisk]

Well, in the code fix I mentioned, static code analysis wouldn't do it.

However, such a rule would be useful in most cases and no-mixed-transactions sound a good name, as we don't talk about nested transactions.

I would love to work on this, but keep in mind:

• it would be my first open source contribution;
• the last time I did parsing and AST was in CS 15 years ago.

I had a first look on a rule implementation and saw there's some documentation also.

What do you recommend ? Start implementing (test, then code) and read docs when stucked, or read docs first ?

[AntonNiklasson]

Hey, sorry for not getting back to you. Did you get started on this?

Don't worry about this being your first time. It's not as hard as it might seem. A great tip is to use ASTExplorer (configured with espree and ESLint V4) to explore and experiment with the AST.

Let me know if I can help. If you don't have time, just let me know 😊

[GradedJestRisk]

I didn't start yet, but with this feedback I can go on !

[GradedJestRisk]

Two years went by, I'm better choosing an easier rule !