code: function updateExtraColumns (model, instance) {
      // columns to update
      var updateColumns = []
      // placeholder => value params for query
      var params = {}
      // add instance id to params
      params.id = instance.id
      // build list of columns to update and param values
      _.each(model.extraColumns, (spec, name) => {
          // convert boolean to 1/0
          if (spec.type === 'boolean') {
              params[name] = toBooleanInt(_.get(instance.data, spec.path))
          }
          // set other values directly
          else {
              params[name] = _.get(instance.data, spec.path)
          }
          // add update sql
          updateColumns.push(`${quoteName(name)} = ${placeholder(model, name, spec)}`)
      })
      // build sql string
      var sql = `UPDATE ${quoteName(model.name)} SET ${updateColumns.join(', ')} WHERE ${quoteName(model.columnName('id'))} = ${placeholder(model, 'id', {type: 'id'})}`
      // return sql and params to perform query
      return {
          params: params,
          sql: sql,
      }
  }
docs: @function updateExtraColumns
  
  create sql to UPDATE extra columns on table and build params object for query
  
  @param {object} model
  @param {object} data
  
  @returns {object}
  
  @throws {Error}