blocks|key|855446|text|您应该按字母顺序将表命名为要连接的两个型号的名称，并将这两个型号的id放入表中。然后，将每个模型相互连接起来，在模型中创建关联。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|855447|下面是一个例子：|855448|#+in+migration
def+self.up
++create_table+'categories_products',+:id+=>+false+do+%7Ct%7C
++++t.column+:category_id,+:integer
++++t.column+:product_id,+:integer
++end
end

#+models/product.rb
has_and_belongs_to_many+:categories

#+models/category.rb
has_and_belongs_to_many+:products|code-block|syntax|javascript|855449|但这不是很灵活，您应该考虑使用has_many：|855450|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|N|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|O|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

You should name the table the names of 2 models you want to connect by alphabetical order
and put the two model id's in the table.
Then connect each model to each other creating the associations in the model.

Here's an example:

<pre><code># in migration
def self.up
 create_table 'categories_products', :id =&gt; false do |t|
 t.column :category_id, :integer
 t.column :product_id, :integer
 end
end

# models/product.rb
has_and_belongs_to_many :categories

# models/category.rb
has_and_belongs_to_many :products
</code></pre>

But this is not very flexible and you should think about using has_many :through

blocks|key|855486|text|最上面的答案显示了一个综合索引，我认为它不会被用来从橙子中查找苹果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|855487|create_table+:apples_oranges,+:id+=>+false+do+%7Ct%7C
++t.references+:apple,+:null+=>+false
++t.references+:orange,+:null+=>+false
end

#+Adding+the+index+can+massively+speed+up+join+tables.
#+This+enforces+uniqueness+and+speeds+up+apple->oranges+lookups.
add_index(:apples_oranges,+[:apple_id,+:orange_id],+:unique+=>+true)
#+This+speeds+up+orange->apple+lookups
add_index(:apples_oranges,+:orange_id)|code-block|syntax|javascript|855488|我确实找到了答案，这是基于“博士是什么”的有用的讨论，当然也是如此。|855489|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|K|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|L|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|M|8|@]|9|@]|A|$]]|$1|I|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|J|$]]

The top answer shows a composite index that I don't believe will be used to lookup apples from oranges. 

<pre><code>create_table :apples_oranges, :id =&gt; false do |t|
 t.references :apple, :null =&gt; false
 t.references :orange, :null =&gt; false
end

# Adding the index can massively speed up join tables.
# This enforces uniqueness and speeds up apple-&gt;oranges lookups.
add_index(:apples_oranges, [:apple_id, :orange_id], :unique =&gt; true)
# This speeds up orange-&gt;apple lookups
add_index(:apples_oranges, :orange_id)
</code></pre>

I did find the answer this is based on by 'The Doctor What' useful and the discussion certainly so too.

blocks|key|855531|text|在Rails4中，您可以简单地使用|type|unstyled|depth|inlineStyleRanges|entityRanges|data|855532|create_join_table+:table1，：table2|855533|这就是全部。|855534|注意:你必须使用字母数字的table1，table2。|855535|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|J|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|K|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|L|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|M|8|@]|9|@]|A|$]]|$1|H|3|-4|5|6|7|N|8|@]|9|@]|A|$]]]|I|$]]

In rails 4, you can simple use 

create_join_table :table1s, :table2s

it is all. 

Caution: you must offord table1, table2 with alphanumeric.

blocks|key|855554|text|我喜欢这样做：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|855555|rails+g+migration+CreateJoinedTable+model1:references+model2:references。这样我就得到了一个类似于下面这样的迁移：|offset|length|style|CODE|855556|class+CreateJoinedTable+<+ActiveRecord::Migration
++def+change
++++create_table+:joined_tables+do+%7Ct%7C
++++++t.references+:trip,+index:+true
++++++t.references+:category,+index:+true
++++end
++++add_foreign_key+:joined_tables,+:trips
++++add_foreign_key+:joined_tables,+:categories
++end
end|code-block|syntax|javascript|855557|我喜欢在这些列上建立索引，因为我会经常使用这些列进行查找。|855558|entityMap^0|0|0|1Z|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|R|8|@$D|S|E|T|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|U|8|@]|9|@]|A|$K|L]]|$1|M|3|N|5|6|7|V|8|@]|9|@]|A|$]]|$1|O|3|-4|5|6|7|W|8|@]|9|@]|A|$]]]|P|$]]

I like doing:

<code>rails g migration CreateJoinedTable model1:references model2:references</code>. That way I get a migration that looks like this:

<pre><code>class CreateJoinedTable &lt; ActiveRecord::Migration
 def change
 create_table :joined_tables do |t|
 t.references :trip, index: true
 t.references :category, index: true
 end
 add_foreign_key :joined_tables, :trips
 add_foreign_key :joined_tables, :categories
 end
end
</code></pre>

I like having index on these columns because I'll often be doing lookups using these columns.

How do I do a <code>script/generate migration</code> to create a join table for a <code>has_and_belongs_to_many</code> relationship?

The application runs on Rails 2.3.2, but I also have Rails 3.0.3 installed.

Rails migration for has_and_belongs_to_many join table

如何执行script/generate migration来为has_and_belongs_to_many关系创建连接表？这个应用程序运行在Rails 2.3.2上，但我也安装了Rails 3.0.3。

问has_and_belongs_to_many连接表的Rails迁移
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