synchronous query with node and PostgreSQL

Question

I want delete from box_property when all update query finished

I write this code but I'm not sure that this is correct or not.I want run update query synchronous

var data = [1, 2, 3, 4]; //data generate dynamicly  
for (var i = 0; i < BoxData.length; i++) {
    pool.connect(function(err, client, done) {
        client.query("update   box set gamer_id=null where  box_id=$1; ", [data[i]], function(err, resultUpdate) {
            if ((i + 1) == BoxData.length) {
                //when all query finished then run this query
                client.query("delete from box_property where gamer_id=$1;", [gamer_id], function(err, resultUpdate) {})
            }
        })
    })
}

Is there way that run update query sync and after for loop I run delete query?

like this

var data = [1, 2, 3, 4]; //data generate dynamicly  
for (var i = 0; i < BoxData.length; i++) {
    pool.connect(function(err, client, done) {
        client.query("update   box set gamer_id=null where  box_id=$1; ", [data[i]], function(err, resultUpdate) {
        })
    })
}

//when all query finished then run this query
client.query("delete from box_property where gamer_id=$1;", [gamer_id], function(err, resultUpdate) {})

vitaly-t · Accepted Answer · 2017-08-19 18:26:06Z

1

The same logic, implemented the right way, with pg-promise:

var data = [1, 2, 3, 4]; //data generated dynamically

db.tx(t => {
    return t.none('UPDATE box SET gamer_id = null WHERE box_id IN ($1:csv)', [data])
        .then(() => {
            return t.none('DELETE FROM box_property WHERE gamer_id = $1', [gamer_id]);
        });
})
    .then(() => {
        // success
    })
    .catch(error => {
        // error
    });

For one thing, you do not need to do a loop for that type of update, a single WHERE IN will do. And for another, such sequence of changes should be inside a transaction. The example above shows you how to do both at the same time.

edited Aug 19, 2017 at 18:26

answered Sep 17, 2016 at 10:38

vitaly-t

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Comments

Alexey Soshin · Accepted Answer · 2016-09-16 18:28:15Z

1

You should avoid making anything synchronous in NodeJS.

In your case, a simple IN statement should solve that:

var params = [];
for (var i = 1; i <= data.length; i++) {
   params.push("$"+i);
}
 pool.connect(function(err, client, done) {
    client.query("update box " + 
                 " set gamer_id=null " + 
                 " where  box_id in "+params.join(",")+"; ", 
                 [...data], function(err, resultUpdate) {
        client.query("delete from box_property " + 
                     " where gamer_id=$1;", 
                     [gamer_id], function(err, resultUpdate) {})
        })
    })

answered Sep 16, 2016 at 18:28

Alexey Soshin

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2 Comments

ashkufaraz Over a year ago

this query is for example ,is there way that run query sync?

Alexey Soshin Over a year ago

There's no synchronous query in NodeJS. If you need for one action to happen when N other actions complete, either use promises or count callbacks.

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