node-mysql - when to release connection back into pool

Question

I'm using the node-mysql driver with connection pooling.

Releasing the connection back into the pool when there's only one query, is easy:

pool.getConnection(function(err, connection) {
  if (err) {
    throw err;
  }

  query = "SELECT * FROM user WHERE id = ?";
  connection.query(query, [id], function(err, users) {
    connection.release();

    if (err) {
      throw err;
    }

    // ...
  });
});

What if I need to use the connection a second time? I'd have to move the release() down a few lines. But what happens if the error is thrown? Is the connection never returned to the pool?

Do I have to use some control flow lib to have a "finally" moment in which I could release it?
Any better ideas?

Answer 1

One way this could be handled is promises. Since you're building a pool, you can construct your requests with something like q (or native promises, coming soon):

// assuming you have your local getConnection above or imported
exports.getConnection = function(queryParams) {
    var d = q.defer();
    local.getConnection(function(err, conn) {
        if(err) d.reject(err);
        d.resolve(conn);
    });
});

So, wrap few of your other calls into promises like that and then just compose your query:

db.getConnection()
.then(function(conn){
    makeRequest()
    .then(...)
    ...
.catch(function(err){
    // at the end you release the conn
});

Does it seem like something you're asking for?