test002.js

const config = require('config')
const { Pool, Query } = require('pg')

// config constants
const relations = config.get('relations')

let pools = {}

for (relation of relations){
    const [database, schema, view] = relation.split('::')
    if(!pools[database]){
        pools[database] = new Pool({
            host: config.get(`connection.${database}.host`),
            user: config.get(`connection.${database}.dbUser`),
            port: config.get(`connection.${database}.port`),
            password: config.get(`connection.${database}.dbPassword`),
            database: database
        })
    }
    pools[database].connect(async (err, client) => {
        if (err) throw err
        //Getting the list of columns, then adjust it
        let sql = `SELECT column_name FROM information_schema.columns WHERE table_schema = '${schema}' AND table_name = '${view}' ORDER BY ordinal_position`
        let cols = await client.query(sql)
        cols = cols.rows.map(r => r.column_name).filter(r => r !== 'geom') //choose "rows", then its colum_names are listed, and geom is removed.
        //we will add filter if needed
        cols.push(`ST_AsGeoJSON(${schema}.${view}.geom)`)
        //console.log(`columns used: ${cols}`)
        // Then, we will get feature record.
        await client.query('BEGIN')
        sql = `SELECT ${cols.toString()} FROM ${schema}.${view} LIMIT 1`
        cols = await client.query(sql)
        console.log(`${database}-${schema}-${view}`)
        console.log(cols.rows)
        await client.query('COMMIT')
        await client.end()
    })    
}