Firebase transaction api call current data is null

Question

When I use transaction() to update a location, data at that location is returning null even though the location having some da

Answer 1

Simply showing an example implementation to elaborate on @Kato accepted answer above with a custom upsert function:

  /**
   * Transactional insert or update record
   * @param  {String} type - object type (table or index) to build lookup path
   * @param  {String} id - object ID that will be concat with path for lookup
   * @param  {Object} data - new object (or partial with just edited fields)
   * @return {Object}       new version of object
   */
  const upsert = (type, id, data) => {
    return new Promise((resolve, reject) => {
      if (!type) {
        log.error('Missing db object type')
        reject(new TypeError('Missing db object type'))
      }
      if (!id) {
        log.error('Missing db object id')
        reject(new TypeError('Missing db object id'))
      }
      if (!data) {
        log.error('Missing db data')
        reject(new TypeError('Missing db data'))
      }

      // build path to resource
      const path = `${type}/${id}`
      log.debug(`Upserting record '${path}' to database`)

      try {
        const ref = service.ref(path)
        ref.transaction(record => {
          if (record === null) {
            log.debug(`Creating new record`) // TODO: change to debug
            return data
          } else if (record) {
            log.debug(`Updating existing record`) // TODO: change to debug
            const updatedRecord = Object.assign({}, record, data)
            return updatedRecord
          } else {
            return record
          }
        }, (error, committed, snapshot) => {
          if (error) {
            log.error(`Error upserting record in database`)
            log.error(error.message)
            reject(error)
          } else if (committed) {
            log.debug(`Saved update`)
          } else {
            log.debug(`Record unchanged`)
          }

          if (snapshot) {
            resolve(snapshot.val())
          } else {
            log.info(`No snapshot found in transaction so returning original data object`)
            resolve(data)
          }
        })
      } catch (error) {
        log.error(error)
        reject(error)
      }
    })
  }