问题描述
是否可以在 Rails 中向现有记录添加关联，而无需立即将此更改提交到数据库?例如.如果我有 Post has_many :tags
Is it possible in Rails to add an association to an existing record without immediately committing this change to the database?E.g. if I have Post has_many :tags
post.tags << Tag.first
这将立即提交到数据库.我尝试了其他方法而不是 <<，但没有成功(我想要的是在保存父对象时创建关联).是否有可能获得类似使用 build 向新记录添加关联时的行为?
This will commit to database immediately. I've tried other ways instead of <<, but without success (what I want is to create the association when saving the parent object).Is it possible to get behavior like when you are adding association to a new record with build?
post.tags.build name: "whatever"
我认为这在 Rails 中有点不一致，在某些情况下，有一个选项会很有用.
I think this is kind of inconsistent in Rails, in some cases it would be useful to have an option to do this.
换句话说，我想要
post.tags << Tag.first # don't hit the DB here!
post.save # hit the DB here!
推荐答案
这应该适用于 Rails 3.2 和 Rails 4:
This should work in Rails 3.2 and Rails 4:
post.association(:tags).add_to_target(Tag.first)
请参阅此要点:https://gist.github.com/betesh/dd97a331f67736d8b83a
请注意，保存父级会保存子级，并且在保存之前不会设置 child.parent_id.
Note that saving the parent saves the child and that child.parent_id is NOT set until you save it.
编辑 2015 年 6 月 12 日:对于多态记录:
EDIT 12/6/2015:For a polymorphic record:
post.association(:tags).send(:build_through_record, Tag.first)
# Tested in Rails 4.2.5
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