where am I closing the connection in node-mysql? - mysql

Question

Here is my code:
var set = {
FIRST_NAME: professor.value_20,
SURNAME: professor.value_21
}
//logs
//console.log(set);
//executes query
connection.query({
sql: 'SELECT TEACHERID FROM TEACHER WHERE FIRST_NAME = ? AND SURNAME = ?',
//'INSERT INTO TEACHER set ? ON DUPLICATE KEY UPDATE FIRST_NAME = ?, SURNAME = ?',
values: [set.FIRST_NAME,set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
if(results.length < 0) {
connection.query({
sql: 'INSERT INTO TEACHER set ?',
values: [set]
}, (err, results, fields) => {
if (err) throw err;
});
}
else {
connection.query({
sql: 'UPDATE TEACHER (FIRST_NAME, SURNAME) VALUES(?,?)',
values: [set.FIRST_NAME, set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
connection.end();
});
}
});
When I run this code I get the following error:
Error: Cannot enqueue Query after invoking quit.
The problem seems to occur at the level of the third query, although I did not close the connection earlier. How do I fix this?
Another question: is it better in this case to use a pool instead of a direct connection?
Thank you!

Answer 1

How do I fix this?
You have to either remove connection.end() or reestablish connection beforehand.
var connection = mysql.createConnection(config); //establish new connection
connection.query({
sql: 'SELECT TEACHERID FROM TEACHER WHERE FIRST_NAME = ? AND SURNAME = ?',
//'INSERT INTO TEACHER set ? ON DUPLICATE KEY UPDATE FIRST_NAME = ?, SURNAME = ?',
values: [set.FIRST_NAME, set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
if (results.length < 0) {
connection.query({
sql: 'INSERT INTO TEACHER set ?',
values: [set]
}, (err, results, fields) => {
if (err) throw err;
});
} else {
connection.query({
sql: 'UPDATE TEACHER (FIRST_NAME, SURNAME) VALUES(?,?)',
values: [set.FIRST_NAME, set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
connection.end(); //or just remove this line
});
}
});
I don't recommend the above fixes. The best solution is to use pooling connections.
pool.getConnection(function(er,connection){
if(er){
throw er;
}
connection.query({
sql: 'SELECT TEACHERID FROM TEACHER WHERE FIRST_NAME = ? AND SURNAME = ?',
//'INSERT INTO TEACHER set ? ON DUPLICATE KEY UPDATE FIRST_NAME = ?, SURNAME = ?',
values: [set.FIRST_NAME, set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
if (results.length < 0) {
connection.query({
sql: 'INSERT INTO TEACHER set ?',
values: [set]
}, (err, results, fields) => {
if (err) throw err;
});
} else {
connection.query({
sql: 'UPDATE TEACHER (FIRST_NAME, SURNAME) VALUES(?,?)',
values: [set.FIRST_NAME, set.SURNAME]
}, (err, results, fields) => {
if (err) throw err;
});
}
});
});
This approach will remove the overhead of establishing a new connection in each query.