Node.js and mysql Callback : query in query callback

Question

All I want to do is insert some data if my database doesn't have that, so I put Insert SQL into my callback function of my Select SQL, but I got error like this:

{ [Error: Cannot enqueue Query after invoking quit.] code: 'PROTOCOL_ENQUEUE_AFTER_QUIT', fatal: false }

my code snippet is here:

db.query('SELECT count(*) as Resultcount FROM tablename WHERE email = ? and password = ?', [post.email, post.password], function(error, result){
    if (result[0].Resultcount == 0){
        var query2 = db.query('INSERT INTO tablename SET ?', [post], function(err, result) {
            if(err){
              console.log(err);
           }
             console.log(result);
          });
    }
    else{
        console.log('have data already');
    }
});

Could someone give me some advice? Thanks

----update----

actually, the callback function of select SQL is not an anonymous function, my code snippet about db.end() is like this:

var QueryResults = new queryResultFuntion(Back_results);

    db.query('SELECT count(*) as Resultcount FROM tablename WHERE email = ? and password = ?', [post.email, post.password], QueryResults.queryResult );


    db.end();

Are you closing your DB connection somewhere after this code? — loganfsmyth, Apr 21 '13 at 17:59
yes, when I finish db.query('select ...'), I called db.end(); — Arvin, Apr 21 '13 at 18:02
That means that by the time your INSERT query runs, the connection will be closed. Please add that code to your question and I'll make an answer. — loganfsmyth, Apr 21 '13 at 18:04
I move my db.end() to my callback function of Insert SQL, and it works! It seems like I just didn't full understand how asynchronous works... but thank you anyway! — Arvin, Apr 21 '13 at 18:12

score 26 · Accepted Answer · answered Apr 21 '13 at 18:06

26

You db.end() call will queue the connection to close once the SELECT has completed, so when you attempt to do the inner INSERT query, the database connection will have been closed, hence the error PROTOCOL_ENQUEUE_AFTER_QUIT, as you are attempting to queue a new command after the connection is closed.

Depending on how you are creating the connection, you should either move your db.end() call inside the callbacks, or not have a db.end() call at all if the connection is opened on program start.

answered Apr 21 '13 at 18:06

loganfsmyth

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Not doing `db.end()` at all results in having to terminate my script (which I'm starting on the command line with the `node` command) with Ctrl-C. But this did get rid of `PROTOCOL_ENQUEUE_AFTER_QUIT` – Lori Oct 26 '15 at 16:22
5

@Lori Correct, that's why I prefaced it with `Depending on how you are creating the connection`. If you are writing a node server for instance, you'd only open the connection once, and there is no expectation that the server would every exit anyway. If you are writing a script, you'd want to end the connection once all of the operations in your script have completed. – loganfsmyth Oct 26 '15 at 16:24
for me, I placed `connection.end()` or `db.end()` (in your case), outside of the result callback. As a result, it was ending the connection even before the callback has returned. Therefore the error is coming. So I just made sure its inside the `connection.query or db.query` block. `connection.query(sql, (err,result)=> { if(err) throw err; console.log(result) connection.end(); })` – Gel Apr 21 '22 at 14:25

Node.js and mysql Callback : query in query callback

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