Cannot read property 'query' of undefined in Node & Postgresql

Question

const pool = new pg.Pool(config);
var tablename = req.body.tablename;

pool.connect(function (err, client, done) {
    var query_get_value = 'SELECT * FROM '+ tablename;
    client.query(query_get_value, function (err, result) {
        done();
        if (err) {
                throw err;
        }
        var rows = result.rows;
.....

this code runs correctly for a while, but a few seconds later, I received following errors:(I call this function repeatedly on the view side using setInterval function)

 client.query(query_get_value, function (err, result) {
                   ^

TypeError: Cannot read property 'query' of undefined
    at /var/node_project/controllers/index.js:630:10
    at client.connect (/var/node_project/node_modules/pg-pool/index.js:219:9)
    at Connection.connectingErrorHandler (/var/node_project/node_modules/pg/lib/client.js:123:14)
    at Connection.emit (events.js:127:13)
    at Socket.<anonymous> (/var/node_project/node_modules/pg/lib/connection.js:117:12)
    at Socket.emit (events.js:127:13)
    at addChunk (_stream_readable.js:269:12)
    at readableAddChunk (_stream_readable.js:256:11)
    at Socket.Readable.push (_stream_readable.js:213:10)
    at TCP.onread (net.js:598:20)

not related to your problem, but: are you using pg-promise? If so, you should definitely use its built-in query-building system (like client.query('SELECT * FROM $1', tablename)) instead of using string concatenation. Imagine req.body.tablename was [yourtablename]; DROP TABLE [yourtablename]; --... xkcd.com/327 — JSilv
– JSilv, Commented Mar 22, 2018 at 18:24

Stretch0 · Accepted Answer · 2018-03-22 16:35:29Z

2

You are probably getting getting an error and therefore client doens't have the method query because it is undefined.

You can easily wrap it in an if/else block to make sure client is set:

pool.connect(function (err, client, done) {
        if(err) {
            console.log(err)
        }else{
            var query_get_value = 'SELECT * FROM '+ tablename;
        client.query(query_get_value, function (err, result) {
            done();
            if (err) {
                    throw err;
            }
            var rows = result.rows;
        }

answered Mar 22, 2018 at 16:35

Stretch0

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2 Comments

Eric Lee Over a year ago

I also tried like that. but in that case, I received other errors like this: { error: sorry, too many clients already....

Stretch0 Over a year ago

That sounds like the root cause of your problem. Why do you have other clients connecting? You should have one client and close it when you finish querying the DB

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