double precision field not parsed correctly, loss of precision

[gabooh]

I get data from fields in postgresql 9.4 :

create table bookseller
(
...
    maplatitude double precision,
    maplongitude double precision,
...
);

And setting up node-pg like this :

const {Pool} = require('pg')
const types = require('pg').types

types.setTypeParser(701, (val) => {
  console.log(`val double : ${val}`)
  return parseFloat(val)
})

Data from pg looks like this :

maplatitude : 43.84668200000001
maplongitude : 5.559941999999999

But I get this with node-pg, whatever I do (default type parser, or with above override).

maplatitude : 43.846682
maplongitude : 5.559942

The result from node-pg :

Result {
  command: 'SELECT',
  rowCount: 1,
  oid: NaN,
  rows: 
   [ anonymous {
     ...
       maplatitude: 43.846682,
       maplongitude: 5.559942 } ],
  fields: 
...
     Field {
       name: 'maplatitude',
       tableID: 724451,
       columnID: 11,
       dataTypeID: 701,
       dataTypeSize: 8,
       dataTypeModifier: -1,
       format: 'text' },
     Field {
       name: 'maplongitude',
       tableID: 724451,
       columnID: 12,
       dataTypeID: 701,
       dataTypeSize: 8,
       dataTypeModifier: -1,
       format: 'text' } ],

I've read countless bug report and node-pg docs on this, seams like it should work correctly. Is this a bug ? Or something I'm not doing correctly ?

[gabooh]

In case that helps, using pg-native returns the same truncated data :

var Client = require('pg-native')

var client = new Client()
client.connectSync('postgresql://xxxx', (err) => {
  throw err
})

var rows = client.querySync(
  `
    SELECT id, maplatitude, maplongitude 
    FROM xxx 
    WHERE id = xxx
    LIMIT 10
  `)
console.log(rows)

[gabooh]

And I have a workaround : it does not work correctly with double precision type, but it's ok with Numeric type and using setTypeParser. I'll leave this open, as I think the behaviour should be the same with double precision type. There is data loss.

[charmander]

You’ll need to set extra_float_digits (to 3, for example) – see the note at https://www.postgresql.org/docs/10/static/datatype-numeric.html#DATATYPE-FLOAT.

[xajhqffl]

I got similar issues. it is losing precision with node-pg. I used same pg client in Java, it is returning correct value.