我是否需要手动为 HABTM 连接表创建迁移? [英] Do I need to manually create a migration for a HABTM join table?

问题描述

我现在正在努力让 HATBM 正常工作.我有一个被打败的 scanario:文章和标签.我认为这里应该使用 HABTM，因为它是多对多的关系.但是我不知道我是否应该手动创建一个连接表(在这种情况下是 articles_tags).

I'm struggling now to get HATBM working correctly. I have a beaten scanario: articles and tags. I presume, HABTM should be used here, since it is a many-to-many relationship. I don't know however if I should manually create a join table (articles_tags in this case).

我的代码目前如下:

class Article < ActiveRecord::Base
  has_and_belongs_to_many :tags  
end

class Tag < ActiveRecord::Base
  has_and_belongs_to_many :articles
end

当我运行迁移时，没有创建第三个表.另外，我想补充一点，我的第三个表不承载任何域逻辑，只是盲目分配.

When I run the migrations, no 3rd table is created. Also, I would like to add that my third table doesn't bear any domain logic, just blind assignment.

我使用的是 Rails 2.2.2

I'm using Rails 2.2.2

推荐答案

您应该在其中一个表的迁移中执行此操作，或者如果已运行这些迁移，则应在单独的迁移中执行此操作:

You should do this in a migration of one of the tables, or in a separate migration if those migrations have been ran:

create_table :articles_tags, :id => false do |t|
  t.references :article, :tag
end

add_index :articles_tags, [:article_id, :tag_id]

这将为您创建表和 :id =>false 告诉 Rails 不要向这个表添加 id 字段.还有一个索引，可以加快对这个连接表的查找.

This will create the table for you and the :id => false tells Rails not to add an id field to this table. There's an index also, which will speed up lookups for this join table.

您也可以为此生成一个模型 (ArticlesTag) 并执行以下操作:

You could also generate a model (ArticlesTag) for this and do:

# article.rb
has_many :articles_tags
has_many :tags, :through => :articles_tags

# tag.rb
has_many :articles_tags
has_many :articles, :through => :articles_tags

# article_tag.rb
belongs_to :tag
belongs_to :article

然后在从 script/generate modelarticles_tag 调用生成的迁移中创建表.

And then create the table in the migration generated from the script/generate model articles_tag call.

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