Is there a way to check for errors first from inserting in two related rows before saving in database - postgresql

Question

I'm currently making job/task list as a test project to learn web development (REST API, Express.js, Postgresql 13 via pg-node).
The structure is that the user can add employees in various tasks and jobs.
1 job can have multiple tasks
1 task can have multiple employees
Employees cannot have more than 1 task in the same job, but can be assigned another task in a different job.
The flow in the UI is a modal that allows you to fill out the job details (name), add tasks, then assign the employees on the said task.
What I currently have was to create two endpoints being sent when clicking a "Create" button, one that creates the job, and the second that creates and assigns the employees to the tasks as I need to attach the job_id to the task, which I cannot do until it has already been generated/created. The problem with this is that in the case of an error in inserting a task, the job will already be created and saved in the database while failing to assign the task and employees, causing a conflict when the "Create" button in the UI.
What I want to do (if possible) is to create a single query that will do both the creation and insertion of the job and initial tasks and employee assignments. The query will then not save the job in the database if there are errors that occurred during the entire transaction (e.g. a task failed to be inserted due to failing a condition such as wrong data type, etc.).
DB Fiddle for the schema: https://www.db-fiddle.com/f/izPsVVxPZ8e9ZMPwbL9her/10
These are my 2 routes:
//Create Job
const {
name
} = req.body;
const job = await pool.query(`SELECT * FROM jobs WHERE
name = $1)`, [
job_name
]);
if (job.rows.length !== 0) {
return res.status(401).send("Job already exists.");
}
const newJob = await pool.query(
`INSERT INTO jobs (job_name) VALUES
($1) RETURNING *`,
[job_name]
);
res.json({ "message": "Job created successfully!" });
//Assign Task
const {
job_id
employee_id
} = req.body;
const checkTask = await pool.query(`SELECT * FROM treatments WHERE
job_id = $1 AND
employee_id $2`, [
req.params.id, employee_id
]);
if (checkTreatment.rows.length !== 0) {
return res.status(401).send("Technician already assigned in the same treatment and schedule.");
}
const newTaskAssignment = await pool.query(
`INSERT INTO treatments (job_id,
employee_id) VALUES
($1, $2) RETURNING *`,
[req.params.id, job_id]
);
res.json({ "message": "Task added to job successfully!" });
Also, if possible, how can I do bulk insert tasks/employee assignments through the API POST route, I read that it involves making an array, but I haven't delved into it yet, if you can also give me advice for it that would be great (or any resource to read, I'm currently reading documentation and stackoverflow topics).
Thank you in advance for helping it!

Answer 1

UPDATE: I managed to do it via following the tutorial from kb.objectrocket.com
It involves using Transactions (which I just learned last night, and are really awesome!). This is the code that solved my problem:
//2. Declare an asynchronous function for the PG transaction
async function execute() {
// Promise chain for pg Pool client
const client = await pool
.connect()
.catch(err => {
console.log("\nclient.connect():", err.name);
// iterate over the error object attributes
for (item in err) {
if (err[item] = undefined) {
process.stdout.write(item + " - " + err[item] + " ");
}
}
//end the Pool instance
console.log("\n");
process.exit();
});
try {
//Initiate the Postgres transaction
await client.query("BEGIN");
try {
const sqlString = `WITH INSERTED AS (
INSERT INTO jobs (job_name) VALUES
($1) RETURNING id)
INSERT INTO tasks(
employee_id, job_id) VALUES
($1,(
SELECT id FROM inserted
))`;
const sqlValues = [job_name, employee_id
];
// Pass SQL string to the query() method
await client.query(sqlString, sqlValues, function(err, result) {
console.log("client.query() SQL result:", result);
if (err) {
console.log("\nclient.query():", err);
// Rollback before executing another transaction
client.query("ROLLBACK");
console.log("Transaction ROLLBACK called");
} else {
client.query("COMMIT");
console.log("client.query() COMMIT row count:", result.rowCount);
}
});
} catch (er) {
// Rollback before executing another transaction
client.query("ROLLBACK");
console.log("client.query():", er);
console.log("Transaction ROLLBACK called");
}
} finally {
client.release();
console.log("Client is released");
}
}
execute();
res.json({ "message": "Service job created successfully!" });
} catch (err) {
console.error(err.message);
res.status(500).send("Server Error");
}
});
Thank you!