JSON Parse error: Unterminated string after fetching json object

Question

Im stuck with the following problem:

I am fetching a json object from my nodejs backend that is a result of the following MYSQL operation

app.get('/get_events/:playgroundId',  cors(), function(req,res){

    var playgroundId = req.params.playgroundId;

    var sql = "SELECT date as date, CONCAT('[',GROUP_CONCAT(JSON_OBJECT('id', event_id,'time', time,'admin_id', admin_id,'playground_id', playground_id,'event_name', event_name,'description', description,'mode', mode,'type', type,'members', members,'waiting', waiting,'invited', invited)),']') AS list FROM xxx.events where playground_id = '"+playgroundId+"' GROUP BY DATE(date) ORDER BY DATE(date)";
    pool.query(sql, function(err, results) {
        if(err) {
            console.log(err)
            return res.send(err)
        } else {
            return res.json({
                data: results
            })
        }
    });
});

On the client side (which is a react app) im using the following fetch:

fetch(`${global.x}/get_events/${playgroundId}`)
    .then((res) => res.json())
    .then((res) => {
        const data = res.data  
        return data
    
    }).catch((error) => {
      //console.log(error)
    });

the whole thing basically return a grouped by date json response about events that i got in the database. The final data looks like this:

Array [ Object { "date": "2021-03-17T14:52:18.000Z", "list": "[{"id": "cd66d921-8688-11eb-909e-06a351dd0cca", "mode": "Public", "time": "2021-03-16 19:52:18.000000", "type": "Game", "invited": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "members": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "waiting": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "admin_id": "ucLYuwevW5f2uTjdCZpVLBay6kq1", "event_name": "Ttt", "description": "Vvv", "playground_id": "a32bb687-7ae3-11eb-909e-06a351dd0cca"},{"id": "e2ecc0e4-868a-11eb-909e-06a351dd0cca", "mode": "Public", "time": "2021-03-16 21:07:06.000000", "type": "Game", "invited": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "members": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "waiting": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "admin_id": "ucLYuwevW5f2uTjdCZpVLBay6kq1", "event_name": "Tt", "description": "Ggg", "playground_id": "a32bb687-7ae3-11eb-909e-06a351dd0cca"},{"id": "eed0ee4c-8688-11eb-909e-06a351dd0cca", "mode": "Public", "time": "2021-03-16 19:52:18.000000", "type": "Game", "invited": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "members": ["ucLYuwevW5f2uTjdCZpVLBay6kq1"], "waiting": ["ucLYuwe]", }, ]

If i just have 2 events in the DB, the string is properly closed and there is no error. But once I have more than 2 events in there, it seems that the string becomes too long or something and just ends abruptly without proper escapes.

I am not sure whether there is a limit on characters coming from the DB or whether is a json parsing part on the client side.

The error I get in the terminal: SyntaxError: JSON Parse error: Unterminated string

If anybody had similar issues, could you please help.

Thank you!

As a first step I would test your query directly on the DB and see if you get a full JSON object there. That will tell you if the DB is causing any truncation or anything. Then step through the code one line at a time to see if it is returned as a full string. If it is, then some other step is causing the truncation. — Brad
– Brad, Commented Mar 16, 2021 at 19:51
I think i mostly figured it out. It is probably a group_concat_max_len parameter. It is defaulted to 1024. I will play with that and will post an answer later today — Nikita Voevodin
– Nikita Voevodin, Commented Mar 16, 2021 at 20:16

Nikita Voevodin · Accepted Answer · 2021-03-17 23:01:32Z

1

Changing group_concat maximum length like so: SET GLOBAL group_concat_max_len = 100000; fixed it. Had to move the DB inhouse cuz aws rds wouldnt allow changing the default length.

answered Mar 17, 2021 at 23:01

Nikita Voevodin

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