Knex creating database and inserting data to it - mysql

Question

I am using Knex with node.js to create a table and insert some data to it. First I was first creating table and then inserting data but it ended up so that sometimes table was not created yet when data was going to be inserted. Then I ended up using callbacks like below. Now I'm mixing callbacks and promises and I'm not sure if it's very good thing. What could I do to make following work without callback and still take care that table is created before inserting data?
function executeCallback(next, tableName) {
knex.schema.hasTable(tableName)
.then((exists) => {
if (!exists) {
debug('not exists');
// Table creation for mysql
knex.raw(`CREATE TABLE ${tableName} ( id INT(6) UNSIGNED AUTO_INCREMENT PRIMARY KEY, timestamp BIGINT NOT NULL, deviceId VARCHAR(255) NOT NULL, data JSON )`)
.then((rows) => {
debug(rows);
next('Table created (mysql)');
})
.catch((err) => {
debug(`Error: ${err}`);
next(`Error: ${err}`);
});
} else {
debug('Table exists');
next('Table exists');
}
});
}
.
executeCallback((response) => {
debug('back from callback', response);
debug('insert');
knex(req.body.tableName).insert({
timestamp: req.body.timestamp,
deviceId: req.body.deviceId,
data: req.body.data,
})
.catch((err) => {
debug(`Error: ${err}`);
res.status(500).json({ success: false, message: `Error: ${err}` });
})
.then((dataid) => {
debug(`Inserted with id: ${dataid}`);
res.status(201).json({ success: true });
});
}, req.body.tableName);

Answer 1

In general mixing callbacks and Promises is discouraged. I would suggest looking into the async/await pattern for using Promises, as that is often easier to read in code. It works well with knex js too.
One trick with Node callbacks is the convention of the function parameters, where the first parameter is the error, and the second is the success result. Like this: function (error, results) {...} This makes the result easy to check, like
if(error) {
// do error stuff
return
}
// do success stuff with `results`
One could call that function like next(new Error('bad')) for an error, or next(null, 'success object') for a success.
Your callback next is only taking one parameter, and you are not checking its value. It matters whether the result was 'Table Exists' 'Table Created' or 'Error' to what you do next.
You might try something like this:
async function handleInsert(tableName, res) {
try {
let hasTable = await knex.schema.hasTable(tableName)
if(!exists) {
let createResult = await knex.raw(`CREATE TABLE...`)
// check create results, throw if something went wrong
}
//table guaranteed to exist at this point
let insertResult = await knex(req.body.tableName).insert({
timestamp: req.body.timestamp,
deviceId: req.body.deviceId,
data: req.body.data,
})
debug(`Inserted with id: ${insertResult}`) //might need insertResult[0]
res.status(201).json({ success: true })
} catch(err) {
// any error thrown comes here
console.log('Server error: ' + err)
res.error('Bad thing happened, but do not tell client about your DB')
}
}
One more thing. In general, you can either assume the tables you need exist already. Or use a migration to build your DB on server start/update.