bookshelf.js - Selecting certain columns from associations

gistfile1.js

// Select specified columns on relations when fetching:

new models.Post({id:1}).fetch({
  withRelated: [{'tags': function(qb) { qb.column('tags.id') }}]
}).then(function(post) {
  return post.related('tags').toJSON()
})

=> [ { id: 1, parent: undefined } ]

// knex querybuilder debug:

{ method: 'select',
  options: undefined,
  bindings: [ 'permalinks', 1 ],
  sql: 'select "settings".* from "settings" where "settings"."key" = ? limit ?',
  __cid: '__cid13' }
{ method: 'select',
  options: undefined,
  bindings: [ 1, 1 ],
  sql: 'select "posts".* from "posts" where "posts"."id" = ? limit ?',
  __cid: '__cid13' }
{ method: 'select',
  options: undefined,
  bindings: [ 1 ],
  sql: 'select "tags"."id", "posts_tags"."post_id" as "_pivot_post_id", "posts_tags"."tag_id" as "_pivot_tag_id" from "tags" inner join "posts_tags" on "posts_tags"."tag_id" = "tags"."id" where "posts_tags"."post_id" in (?)',
  __cid: '__cid13' }