Rails acts_as_taggable - tagged_with 通过关系

Question

假设我有一个 User / Post 模型，就像这里的例子：

https://github.com/mbleigh/acts-as-taggable-on#tag-cloud-calculations

User 有很多 Post 个，Post 个属于 User。 Post 有标签。我可以轻松搜索具有特定标记的用户 post 吗？

Answer 1

所以你基本上有：

class User
  has_many :posts
end

class Post
  acts_as_taggable

  # under the hood, this declaration creates
  # following relations
  has_many :tags
  has_many :taggings
end

您现在可以将以下关系添加到 User：

class User
  has_many :posts
  has_many :tags, through: :posts
  # has_many :taggings, through: :posts
end

现在查询给定的 @tag 应该很容易：

users_with_give_tag = User.joins(:tags).where("tags.id=?", @tag.id)

产生以下 SQL:

SELECT "users".* FROM "users"
INNER JOIN "posts" ON "posts"."user_id" = "users"."id"
INNER JOIN "taggings" ON "taggings"."taggable_id" = "posts"."id" AND "taggings"."context" = ? AND "taggings"."taggable_type" = ?
INNER JOIN "tags" ON "tags"."id" = "taggings"."tag_id"
WHERE (tags.id=1)  [["context", "tags"], ["taggable_type", "Post"]]

Rails acts_as_taggable - tagged_with 通过关系

Rails acts_as_taggable - tagged_with through a relation

activerecord

ruby-on-rails

acts-as-taggable-on