blocks|key|328700|text|不应向旧迁移添加新行。迁移是建立数据库的一个步骤。最后一次执行的迁移次数存储在schema中，如果使用will+use+rake+db:migrate，则不会运行或重做迁移。如果您之前在创建表的情况下运行迁移，那么您应该在可以使用add_column方法的地方创建新的迁移。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|328701|entityMap^0|13|6|1O|F|37|A|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

You should not add new rows to old migrations. Migration is a step of building database. And number of last executed migration is stored in <code>schema</code>, and it will not be run or redone if you use will use <code>rake db:migrate</code>. If you run the migration with creating the table before, then you should create new migration where you may use <code>add_column</code> method.

blocks|key|111308|text|正如Speransky建议的那样，您永远不应该修改旧的迁移文件。相反，您应该创建一个添加所需列的新迁移。例如，在这种情况下，您可以在应用程序中运行以下命令来创建新的迁移：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|111309|rails+generate+migration+AddListIdColumnToIdeas+list_id:integer|code-block|syntax|javascript|111310|Rails会自动生成迁移文件，剩下的唯一要做的就是运行rake+db:migrate。|offset|length|style|CODE|111311|如果您坚持要修改旧的迁移文件，您可以像以前一样添加该列，并运行以下命令：|111312|rake+db:drop
rake+db:create
rake+db:migrate|111313|这将销毁您当前的数据库，创建一个新数据库并运行所有迁移(包括您的新列)。|111314|entityMap^0|0|0|R|F|0|0|0|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|V|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|W|8|@$I|X|J|Y|K|L]]|9|@]|A|$]]|$1|M|3|N|5|6|7|Z|8|@]|9|@]|A|$]]|$1|O|3|P|5|D|7|10|8|@]|9|@]|A|$E|F]]|$1|Q|3|R|5|6|7|11|8|@]|9|@]|A|$]]|$1|S|3|-4|5|6|7|12|8|@]|9|@]|A|$]]]|T|$]]

As Speransky suggested, you should never modify old migration files. Rather you should create a new migration that adds the desired column. For instance, in this case you would run the following command in your app to create the new migration:

<pre><code>rails generate migration AddListIdColumnToIdeas list_id:integer
</code></pre>

And Rails would generate the migration file automatically and the only thing left to do is run <code>rake db:migrate</code>.

If you insist on modifying the old migration file, you can add the column as you did and run the following:

<pre><code>rake db:drop
rake db:create
rake db:migrate
</code></pre>

Which will destroy your current database, create a new one and run all the migrations (which will include your new column).

blocks|key|111362|text|迁移文件的名称中包含日期时间编码，因此rails会运行此迁移，除非您执行回滚，否则不会再次运行此迁移|type|unstyled|depth|inlineStyleRanges|entityRanges|data|111363|迁移的魔力来了，只需很小的步骤就可以构建您的db，因此在运行rake+db:migrate之后不需要更新迁移，您应该进行新的迁移，以便对db模式进行您想要的更改。|111364|记住要|111365|删除旧迁移文件中添加的行，因为如果您决定回滚此迁移，它可能会引发错误|111366|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|$]]

migration file name has the datetime encoded in its name so rails run this migration one and do not run it again unless you do a rollback
and here come the magic of migration to build you db with small steps so no need to update a migration after run rake db:migrate , you should make a new migration to do the change you want to your db schema
<h2>and remember to</h2>
remove the added line form the old migration file as it might raise errors if you decided to rollback this migration

blocks|key|111403|text|如果要向现有数据库添加新列，则应使用rails+generate+migration。因此，您可以尝试使用rails+generate+migration+add_list_id_to_ideas+list_id:integer，然后使用rake+db:migrate提交此更改。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|111404|entityMap^0|I|O|1H|1P|3B|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]|$9|K|A|L|B|C]|$9|M|A|N|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|O|8|@]|D|@]|E|$]]]|G|$]]

If you want to add a new column to an exist database, you should use <code>rails generate migration</code>. So you can try <code>rails generate migration add_list_id_to_ideas list_id:integer</code> and then use <code>rake db:migrate</code> to commit this change.

blocks|key|328883|text|如果您已经在migrate文件夹中有文件，您只需在其中添加所需的列(只需键入代码)，删除development.sqlite或代表您的db文件的任何内容，然后运行rake+:migrate。然后，它将在表中创建一个包含新列的新sqlite文件，您可以在schema.rb中对其进行检查|type|unstyled|depth|inlineStyleRanges|entityRanges|data|328884|因此，基本上，您所做的一切似乎都很好，除了您没有删除数据库文件。这样做对我来说似乎是最简单的，尽管你会丢失数据库中的所有文件。如果你只是在测试和开发Rails应用，这是可行的。除了我写的内容之外，有没有人能评论一下这种方法是否有问题？|328885|编辑:实际上我在这里找到了一个答案，Editing+Existing+Rails+Migrations+is+a+good+idea?|offset|length|328886|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/10812111/editing-existing-rails-migrations-is-a-good-idea?rq=1^0|0|0|I|1D|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|Q|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@$F|S|G|T|1|U]]|A|$]]|$1|H|3|-4|5|6|7|V|8|@]|9|@]|A|$]]]|I|$J|$5|K|L|M|A|$N|O]]]]

If you already have files in your migrate folder, you could just add column you want there(just type the code), delete development.sqlite or whatever represents your db file, and run rake db:migrate.
It will then create a new sqlite file with new column in table, and you can check it in schema.rb

So, basically, everything you did seems good, except you didn't delete your database file. 
Doing this seems the easiest for me, all though you will lose all the files in your database. If you're just testing and developing Rails app, this works.
Can anyone comment if there is something wrong with this approach, besides what i wrote?

Edit: I actually found an answer about that here
<a href="https://stackoverflow.com/questions/10812111/editing-existing-rails-migrations-is-a-good-idea?rq=1">Editing Existing Rails Migrations is a good idea?</a>

blocks|key|111462|text|你也可以这样做..|type|unstyled|depth|inlineStyleRanges|entityRanges|data|111463|rails+g+migration+add_column_to_users+list_id:string|offset|length|style|CODE|111464|然后是rake+db:migrate|111465|还有你的用户控制器中的add+:list_id属性；|111466|有关更多详细信息，请查看http://guides.rubyonrails.org/active_record_migrations.html|111467|entityMap|0|LINK|mutability|MUTABLE|url|http://guides.rubyonrails.org/active_record_migrations.html^0|0|0|1G|0|3|F|0|B|C|0|C|1N|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|W|8|@$D|X|E|Y|F|G]]|9|@]|A|$]]|$1|H|3|I|5|6|7|Z|8|@$D|10|E|11|F|G]]|9|@]|A|$]]|$1|J|3|K|5|6|7|12|8|@$D|13|E|14|F|G]]|9|@]|A|$]]|$1|L|3|M|5|6|7|15|8|@]|9|@$D|16|E|17|1|18]]|A|$]]|$1|N|3|-4|5|6|7|19|8|@]|9|@]|A|$]]]|O|$P|$5|Q|R|S|A|$T|U]]]]

You can also do this ..

<code>rails g migration add_column_to_users list_id:string</code>

then <code>rake db:migrate</code>

also <code>add :list_id</code> attribute in your user controller ;

for more detail check out <a href="http://guides.rubyonrails.org/active_record_migrations.html" rel="nofollow noreferrer">http://guides.rubyonrails.org/active_record_migrations.html</a>

I'm getting an error:

<pre><code>SQLite3::SQLException: no such column: ideas.list_id: 
SELECT "ideas".* FROM "ideas" 
WHERE "ideas"."list_id" = 2
</code></pre>

But I added 

<code>t.integer :list_id</code>

to my db migration file:

<pre><code>class CreateIdeas &lt; ActiveRecord::Migration
 def change
 create_table :ideas do |t|
 t.string :name
 t.text :description
 t.string :picture

 t.timestamps
 end
 add_foreign_key :ideas, :lists
 end
end
</code></pre>

which gave me this:

<pre><code>class CreateIdeas &lt; ActiveRecord::Migration
 def change
 create_table :ideas do |t|
 t.string :name
 t.text :description
 t.string :picture
 t.integer :list_id
 t.timestamps
 end
 add_foreign_key :ideas, :lists
 end
end
</code></pre>

and then I typed

<pre><code>rake db:migrate
</code></pre>

Any idea why I would be getting an error saying there's no column? I'm still new to RoRs. Do I have to add a column some other way?

Thanks

Ruby on Rails: adding columns to existing database

数据库

我收到一个错误：SQLite3::SQLException: no such column: ideas.list_id: SELECT "ideas".* FROM "ideas"  WHERE "ideas"."list_id" = 2但我补充说t.integer :list_id到我的数据库迁移文件：class ...

问Ruby on Rails:向现有数据库添加列
EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby on Rails:向现有数据库添加列EN

社区

活动

资源

关于

腾讯云开发者

热门产品

热门推荐

更多推荐

问Ruby on Rails:向现有数据库添加列
EN