Cannot use a session that has ended

Question

Sorry to bother you all but we have been facing this problem with this code.

app.get('/site', (req, res, next) => {
    let listOfScreens = [];
    const client = MongoClient.connect(url, function(err, db) {
        if (err) throw err;
        var database = db.db("Webxplorerdb");
        let category = req.query.category;
        let nbScreen = req.query.nb;
        let randomNum;
        let site;
        let social;
        let i;
        if (category == 0) {
            social = database.collection('Social Media');

            for (i = 0; i < nbScreen; i++) {
                randomNum = Math.floor(Math.random() * socialmediadocs);
                site = social.findOne({ _id: randomNum },
                    function(err, result) {
                        if (err) throw err;
                        listOfScreens.push(result);
                    })
            }
            res.json(listOfScreens);
            db.close();
        }
    });
});

I have only shown a part of the code but the rest is the same if condition but with different variables. The problem that we get is that we either get the error "Cannot use a session that has ended" or if we delete the db. close() line, the server sends an empty list(due to the declaration of listOfScreens before) instead of a list of documents that we get from the db with each iteration. So my question is how to solve that problem. I thank you all in advance for your answers.

Answer 1

The reason this doesn't work is the usage of NEW.contract_id in the AFTER DELETE trigger:

UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = NEW.contract_id;

Per the Triggers on Data Changes documentation, NEW is NULL for DELETE triggers.

Updating the code to use OLD instead of NEW fixes the issue:

CREATE OR REPLACE FUNCTION update_campaign_target() RETURNS trigger AS $update_campaign_target$
    BEGIN
        IF TG_OP = 'DELETE'
        THEN
            UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = OLD.contract_id;
        ELSE
            UPDATE contracts SET updated_at = now() WHERE contracts.contract_id = NEW.contract_id;
        END IF;
        RETURN NULL;
    END;
$update_campaign_target$ LANGUAGE plpgsql;

Thanks to Anthony Sotolongo and Belayer for your help!