Promise-MySQL cannot release connections back to the pool - mysql

Question

I am very new to Node.js development and I am working on an app that requires me to pull users from a mysql database. I am using the promise-mysql library to query a mysql database. I am trying to use a connection pool like this:
var pool = mysql.createPool({
host: hgh.host,
user: hgh.user,
password: hgh.pw,
database: hgh.name,
connectionLimit: 10
});
As a global variable in my module.
I then have the above function to return a connection from the pool.
function connect() {
return pool.getConnection().then(function(connection) {
return connection
}).catch(function(error) {
console.log("Connect failed");
throw ErrorModel.generateErrorObject(error, 500);
});
}
Below is a function I am using to query the database with:
function getUser(username) {
var sql_query = `SELECT * FROM userstable WHERE userName = ` + `'` + username + `'`;
return connect().then(function(conn) {
return conn.query(sql_query).then(function(rows) {
console.log("HGH getUser Then");
console.log(pool);
conn.release();
return rows;
});
}).catch(function(error) {
console.log("HGH getUser Catch");
console.log(error);
throw ErrorModel.generateErrorObject(error, 500);
});
}
I am getting this issue:
conn.release is not a function when trying to release my current connection into the pool. Is my logic wrong here? My goal is to have a pool with a bunch of connections (up to a certain number) and if a user needs to query, the getConnection() function just grabs them either a free connection from the pool, or creates them one. Problem is I cannot for the life of me release it back to the pool as free..Every time I make a request with conn.end() instead of release the connection remains in the _allConnections array of the pool when I console it out, and there are absolutely no connections in the _freeConnections array.
Anyone know how I can make connections free again??

Answer 1

Looking at the module's code I found the function for releasing a connection from a pool:
pool.prototype.releaseConnection = function releaseConnection(connection) {
//Use the underlying connection from the mysql-module here:
return this.pool.releaseConnection(connection.connection);
};
So if all of these functions live in the same file you could do the following in the getUser function:
replace
conn.release();
with
pool.releaseConnection(conn);

Answer 2

Looking at the code, promise-mysql wraps the original connection object, which doesn't expose the release method. However, the original is exposed as a property called connection, so this works:
conn.connection.release();
A few random thoughts:
You should probably escape your query input:
var sql_query = `SELECT * FROM userstable WHERE userName = ${ pool.escape(username) }`;
Your code doesn't release connections when an error occurs (because the code in the .then() callback wouldn't get called); it's better to use .finally() to do the releasing, as that will get called for both resolved and rejected cases:
function connect() {
var conn = null;
return pool.getConnection().then(function(connection) {
conn = connection;
return connection;
}).catch(function(error) {
console.log("Connect failed", error);
}).finally(function() {
if (conn) {
conn.connection.release();
}
});
}