blocks|key|2539499|text|尝尝这个?|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2539500|create_table(:table_name,+:id+=>+false)+do+%7Ct%7C
++t.integer+:id,+:options+=>+'PRIMARY+KEY'
end|code-block|syntax|javascript|2539501|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Try this?

<pre><code>create_table(:table_name, :id =&gt; false) do |t|
 t.integer :id, :options =&gt; 'PRIMARY KEY'
end
</code></pre>

blocks|key|54069|text|这对我不起作用，但以下内容起到了作用：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|54070|create_table(:table_name,+:id+=>+false)+do+%7Ct%7C
++t.column+:id,+'int(11)+PRIMARY+KEY'
end|code-block|syntax|javascript|54071|唯一的问题是你在schema.rb中丢失了它。|54072|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|$]]

That didn't work for me, but the following did:

<pre><code>create_table(:table_name, :id =&gt; false) do |t|
 t.column :id, 'int(11) PRIMARY KEY'
end
</code></pre>

Only problem is that you lose it in the schema.rb.

blocks|key|2749619|text|好吧，这个问题已经过时了，操作员也没有具体说明版本。这里给出的答案对我来说都不适用于这些版本：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2749620|mysql2+0.3.11
rails+3.2.13+
mysql+5.5|code-block|syntax|javascript|2749621|我最终选择了这个：|2749622|class+SomeMigration+<+ActiveRecord::Migration
++#+emulate+a+primary_key+column+without+auto-increment
++#+the+solution+here+is+to+use+a+non-null+integer+id+column+with+a+unique+index
++#+this+is+semantically+different+from+PRIMARY+KEY+in+mysql+but+not
++#+_too_+functionally+different,+the+only+difference+is+that+mysql+enforces
++#+no-more-than-one-primary-key+but+allows+>1+unique+index
++def+up
++++create_table+:foobars,+:id+=>+false+do+%7Ct%7C
++++++t.integer+:id,+:null+=>+false
++++++t.string+:name
++++end
++++add_index+:foobars,+:id,+:unique+=>+true
++end
end|2749623|我希望这能让外面的人省去花时间追踪这件事，或者更糟...使用答案而不检查它对数据库的作用...因为使用旅居者或jim的答案(使用我的依赖项版本)的结果是迁移运行良好，但允许空is，并且允许重复is。我没有尝试Shep的答案，因为我不喜欢db/schema.rb不一致的想法(对Shep来说，明确指出这个缺点%2B1，有时这是一件坏事)|2749624|我不确定这有什么意义，但在这个解决方案中，mysql+describe将其显示为主键，与AR表的默认设置相同:id+...如下所示：|offset|length|style|CODE|2749625|具有AR默认值的表:id|2749626|%2B---------------------%2B--------------%2B------%2B-----%2B---------%2B----------------%2B
%7C+Field+++++++++++++++%7C+Type+++++++++%7C+Null+%7C+Key+%7C+Default+%7C+Extra++++++++++%7C
%2B---------------------%2B--------------%2B------%2B-----%2B---------%2B----------------%2B
%7C+id++++++++++++++++++%7C+int(11)++++++%7C+NO+++%7C+PRI+%7C+NULL++++%7C+auto_increment+%7C|2749627|表中包含我的解决方案：|2749628|%2B--------------%2B--------------%2B------%2B-----%2B---------%2B-------%2B
%7C+Field++++++++%7C+Type+++++++++%7C+Null+%7C+Key+%7C+Default+%7C+Extra+%7C
%2B--------------%2B--------------%2B------%2B-----%2B---------%2B-------%2B
%7C+id+++++++++++%7C+int(11)++++++%7C+NO+++%7C+PRI+%7C+NULL++++%7C+++++++%7C|2749629|这有点有趣，因为使用我的解决方案迁移生成的SQL不包括“主键”(当然)……但如果使用AR+default+:id，则会...因此，至少对于describe而言，mysql似乎将非空的唯一索引键视为主键。|2749630|HTH某人|2749631|entityMap^0|0|0|0|0|0|R|8|0|0|0|0|0|1X|8|0|0^^$0|@$1|2|3|4|5|6|7|16|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|17|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|18|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|19|8|@]|9|@]|A|$E|F]]|$1|K|3|L|5|6|7|1A|8|@]|9|@]|A|$]]|$1|M|3|N|5|6|7|1B|8|@$O|1C|P|1D|Q|R]]|9|@]|A|$]]|$1|S|3|T|5|6|7|1E|8|@]|9|@]|A|$]]|$1|U|3|V|5|D|7|1F|8|@]|9|@]|A|$E|F]]|$1|W|3|X|5|6|7|1G|8|@]|9|@]|A|$]]|$1|Y|3|Z|5|D|7|1H|8|@]|9|@]|A|$E|F]]|$1|10|3|11|5|6|7|1I|8|@$O|1J|P|1K|Q|R]]|9|@]|A|$]]|$1|12|3|13|5|6|7|1L|8|@]|9|@]|A|$]]|$1|14|3|-4|5|6|7|1M|8|@]|9|@]|A|$]]]|15|$]]

Okay, the question is old and the OP did not specify versions. None of the answers given here worked for me with these versions:

<pre><code>mysql2 0.3.11
rails 3.2.13 
mysql 5.5
</code></pre>

I ended up going for this:

<pre class="lang-rb prettyprint-override"><code>class SomeMigration &lt; ActiveRecord::Migration
 # emulate a primary_key column without auto-increment
 # the solution here is to use a non-null integer id column with a unique index
 # this is semantically different from PRIMARY KEY in mysql but not
 # _too_ functionally different, the only difference is that mysql enforces
 # no-more-than-one-primary-key but allows &gt;1 unique index
 def up
 create_table :foobars, :id =&gt; false do |t|
 t.integer :id, :null =&gt; false
 t.string :name
 end
 add_index :foobars, :id, :unique =&gt; true
 end
end
</code></pre>

I hope that saves someone out there from spending time tracking this down, or worse ... using the answer without checking what it does to the db ... because the result of using either sojourner's or jim's answers (with my versions of the dependencies) is that the migration runs fine but NULL ids are allowed, and duplicate ids are allowed. I did not try Shep's answer because I don't like the idea of db/schema.rb being inconsistent (+1 to Shep for being explicit about that shortcoming, sometimes that'd be a Bad Thing)

I'm not sure the significance of this, but with this solution, mysql <code>describe</code> shows it as a primary key, same as an AR table with default :id ... as in:

table with AR default :id 

<pre><code>+---------------------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+---------------------+--------------+------+-----+---------+----------------+
| id | int(11) | NO | PRI | NULL | auto_increment |
</code></pre>

table with my solution:

<pre><code>+--------------+--------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+--------------+--------------+------+-----+---------+-------+
| id | int(11) | NO | PRI | NULL | |
</code></pre>

which is sort of interesting because the SQL generated by the migration with my solution does not include "PRIMARY KEY" (of course) ... but with AR default :id it does ... so it seems mysql, at least for <code>describe</code> treats a non-null unique-indexed key as a primary key

HTH someone

blocks|key|53614|text|您可以像这样创建一个表：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|53615|class+CreateUsers+<+ActiveRecord::Migration
++def+change
++++create_table+:routers,+{+id:+false+}+do+%7Ct%7C
++++++t.integer+:id
++++end

++++execute+"ALTER+TABLE+routers+ADD+PRIMARY+KEY+(id);"
++end
end|code-block|syntax|javascript|53616|这在Rails+4.0.2和Postgresql+9.3.2中确实有效。|53617|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|$]]

You can create a table like this:

<pre><code>class CreateUsers &lt; ActiveRecord::Migration
 def change
 create_table :routers, { id: false } do |t|
 t.integer :id
 end

 execute "ALTER TABLE routers ADD PRIMARY KEY (id);"
 end
end
</code></pre>

And that really works in Rails 4.0.2 and Postgresql 9.3.2.

blocks|key|2539667|text|要从Rails5开始禁用自动递增，您可以简单地传递|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2539668|default:+nil|code-block|syntax|javascript|2539669|例如|2539670|create_table+:table_name,+id:+:bigint,+default:+nil+do+%7Ct%7C
++#+...+fields+...
end|2539671|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

To disable auto increment as of Rails 5 you can simply pass


<pre><code>default: nil
</code></pre>

for instance

<pre><code>create_table :table_name, id: :bigint, default: nil do |t|
 # ... fields ...
end
</code></pre>

blocks|key|2539703|text|++def+change
++++create_table+:tablename+do+%7Ct%7C
++++++#+t.string+:fieldname
++++end

+++change_column+:tablename,+:id,+:bigint,+auto_increment:+false
+end|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|2539704|注意:从Rails5.1开始，默认的主键是bigint。http://www.mccartie.com/2016/12/05/rails-5.1.html|unstyled|offset|length|2539705|如果您想要4字节密钥更改:bigint为:integer|2539706|entityMap|0|LINK|mutability|MUTABLE|url|http://www.mccartie.com/2016/12/05/rails-5.1.html^0|0|S|1D|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|T|8|@]|9|@$G|U|H|V|1|W]]|A|$]]|$1|I|3|J|5|F|7|X|8|@]|9|@]|A|$]]|$1|K|3|-4|5|F|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

<pre><code> def change
 create_table :tablename do |t|
 # t.string :fieldname
 end

 change_column :tablename, :id, :bigint, auto_increment: false
 end
</code></pre>

Notice: Since Rails 5.1 default primary keys are bigint. <a href="http://www.mccartie.com/2016/12/05/rails-5.1.html" rel="nofollow noreferrer">http://www.mccartie.com/2016/12/05/rails-5.1.html</a>

If you want 4-byte key change :bigint to :integer

Is it possible to create primary key without <code>auto_increment</code> flag in ActiveRecord?

I can't do 

<pre><code>create table :blah, :id =&gt; false
</code></pre>

because I want to have primary key index on the column. I looked up <a href="http://ar.rubyonrails.org/" rel="noreferrer">documentation</a> but didn't find anything useful.

Is it possible to create primary key without auto_increment?

How to turn off auto_increment in Rails Active Record

数据库

是否可以在ActiveRecord中创建不带auto_increment标志的主键我做不到create table :blah, :id => false因为我想在列上建立主键索引。我查了一下，但没有找到任何有用的东西。可以在没有auto_increment的情况下创建主键吗？

问如何在Rails活动记录中关闭auto_increment
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