Helpful utility for converting postgis data into GeoJSON as it comes out of the db, and vice versa.

postgis-geojson-liaison.js

var wkx = require('wkx')
var pg = require('pg')
var pgUtil = require('pg/lib/utils')

const geoParser = {
  init(knex){
    // 1. Convert postgis data coming out of the db into geoJSON
    // Every postgres installation will have different oids for postgis geo types.
    knex
      .raw('SELECT oid, typname AS name FROM pg_type WHERE typname IN (\'geography\', \'geometry\');')
      .then(({rows}) => {
        if (!rows || !rows.length){
          // TODO: this is currently fatal - should it be graceful?
          throw new Error('postgis not installed')
        }
        rows.forEach(({oid, name}) =>
          pg.types.setTypeParser(oid, (val) => geoParser.postgisToGeoJSON(val))
        )
      })

    // 2. Convert geoJSON data going into the database into postgis
    // node-postgres recommends overwriting this function for custom handling
    const oldPrepare = pgUtil.prepareValue
    pgUtil.prepareValue = function(val){
      if (val && typeof val === 'object' && val.type && val.coordinates){
        // quacks like a geoJSON object
        const value = geoParser.geoJSONToPostgis(val)
        return value
      }
      return oldPrepare.call(pgUtil, val)
    }
  },
  postgisToGeoJSON(val){
    const wkbBuffer = new Buffer(val, 'hex')
    const geometry = wkx.Geometry.parse(wkbBuffer)
    return geometry.toGeoJSON()
  },
  geoJSONToPostgis(val){
    if (typeof val === 'object'){
      const parsed = wkx.Geometry.parseGeoJSON(val)
      return parsed.toEwkt()
    }
    return val
  }
}

module.exports = geoParser