blocks|key|1250572|text|rake+db:migrate:status+(Rails+3到5)或rails+db:migrate:status+(Rails+5)可以做到这一点。参见this+commit。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1250573|up表示迁移已运行。down表示迁移尚未运行。|1250574|entityMap|0|LINK|mutability|MUTABLE|url|https://github.com/rails/rails/commit/8e3e117dbe58fd4fedbb78a3d8e398ab0e415634^0|0|M|Z|N|26|B|0|0|0|2|A|4|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@$9|U|A|V|1|W]]|E|$]]|$1|F|3|G|5|6|7|X|8|@$9|Y|A|Z|B|C]|$9|10|A|11|B|C]]|D|@]|E|$]]|$1|H|3|-4|5|6|7|12|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

<code>rake db:migrate:status</code> (Rails 3 to 5) or <code>rails db:migrate:status</code> (Rails 5) will accomplish this. See <a href="https://github.com/rails/rails/commit/8e3e117dbe58fd4fedbb78a3d8e398ab0e415634" rel="noreferrer">this commit</a>.

<code>up</code> means the migration has been run. <code>down</code> means the migration has not been run.

blocks|key|1250501|text|有rake+db:abort_if_pending_migrations+(至少在Rails+2.3.3中，不确定它是什么时候引入的)。描述说“如果有挂起的迁移，则会引发错误”。这似乎更多地被用作其他任务的先决条件，但我猜您可以将其用于您的目的。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1250502|编辑:以下是刚刚生成且未运行“测试”迁移后的输出示例|1250503|rails_project+theIV$+rake+db:abort_if_pending_migrations
(in+/Users/theIV/Sites/rails_project/)
You+have+1+pending+migrations:
++20090828200602+Test
Run+"rake+db:migrate"+to+update+your+database+then+try+again.|code-block|syntax|javascript|1250504|entityMap^0|1|Z|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|R|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|S|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|D|@]|E|$]]]|N|$]]

There is <code>rake db:abort_if_pending_migrations</code> (at least in Rails 2.3.3, not sure when it was introduced). The description says 'Raises an error if there are pending migrations'. This seems to be used more as a prerequisite for other tasks, but I'm guessing you could use it for your purposes.

EDIT: Here is an example of the output after having just generated and not run a 'test' migration

<pre><code>rails_project theIV$ rake db:abort_if_pending_migrations
(in /Users/theIV/Sites/rails_project/)
You have 1 pending migrations:
 20090828200602 Test
Run "rake db:migrate" to update your database then try again.
</code></pre>

blocks|key|1465441|text|rake+db:version将在Rails+2上实现这一点。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1465442|entityMap^0|0|F|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

<code>rake db:version</code> will accomplish this on Rails 2.

blocks|key|1250728|text|这适用于rails+5.2|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1250729|ActiveRecord::Base.connection.migration_context.needs_migration?|code-block|syntax|javascript|1250730|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|$]]

This works for rails 5.2 

<pre><code>ActiveRecord::Base.connection.migration_context.needs_migration?
</code></pre>

blocks|key|1465611|text|如果你想看看有多少迁移已经完成或者挂起，你可以使用下面的命令。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1465612|rails+db:migrate:status|code-block|syntax|javascript|1465613|有关此链接的更多信息：Rails++Active+Record+Migration|offset|length|1465614|entityMap|0|LINK|mutability|MUTABLE|url|https://edgeguides.rubyonrails.org/active_record_migrations.html^0|0|0|B|U|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|T|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|U|8|@]|9|@$I|V|J|W|1|X]]|A|$]]|$1|K|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|L|$M|$5|N|O|P|A|$Q|R]]]]

If you want to see how much migration is done or pending you can see using below command.

<pre><code>rails db:migrate:status
</code></pre>

More on this link: <a href="https://edgeguides.rubyonrails.org/active_record_migrations.html" rel="nofollow noreferrer">Rails Active Record Migration</a>

blocks|key|1465664|text|如果您需要使用bash一行程序来确定是否运行迁移(例如，只有在存在挂起的迁移时才在Heroku+release+phase+command中进行迁移)，这是可行的：|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|1465665|(rails+db:migrate:status+%7C+grep+"%5E\s*down")+&&+rails+db:migrate+%7C%7C+echo+"No+pending+migrations+found."|code-block|syntax|javascript|1465666|entityMap|0|LINK|mutability|MUTABLE|url|https://devcenter.heroku.com/articles/release-phase^0|15|S|0|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@$A|R|B|S|1|T]]|C|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|C|$G|H]]|$1|I|3|-4|5|6|7|V|8|@]|9|@]|C|$]]]|J|$K|$5|L|M|N|C|$O|P]]]]

If you need a bash one-liner to determine whether to run a migration or not (e.g., only migrate in a <a href="https://devcenter.heroku.com/articles/release-phase" rel="nofollow noreferrer">Heroku release phase command</a> when there is a pending migration), this works:

<pre><code>(rails db:migrate:status | grep "^\s*down") &amp;&amp; rails db:migrate || echo "No pending migrations found."
</code></pre>

blocks|key|1250547|text|尝试rake+-h+(帮助)，看看rake+-n+(=+rake+---run)。因此，可能像rake+db：-n这样的命令应该会得到您想要的结果。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1250548|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

Try rake -h (help) and have a look at rake -n (= rake --dry-run). So probably something like rake -n db:migrate should get you what you want.

blocks|key|1465557|text|可能不完全是OP所要求的，但是如果您只是需要快速检查是否有任何迁移等待在rake任务中使用，而不是求助于|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1465558|rake+db:migrate:status+%7C+grep+down+(如果您在Windows上，可能不起作用)|1465559|ActiveRecord::Migration.check_pending！(引发需要救援的ActiveRecord::PendingMigrationError+)|1465560|你能用needs_migration吗？方法：https://apidock.com/rails/v4.0.2/ActiveRecord/Migrator/needs_migration%253F/class|offset|length|1465561|entityMap|0|LINK|mutability|MUTABLE|url|https://apidock.com/rails/v4.0.2/ActiveRecord/Migrator/needs_migration%253F/class^0|0|0|0|N|27|0|0^^$0|@$1|2|3|4|5|6|7|R|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|S|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|T|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|U|8|@]|9|@$H|V|I|W|1|X]]|A|$]]|$1|J|3|-4|5|6|7|Y|8|@]|9|@]|A|$]]]|K|$L|$5|M|N|O|A|$P|Q]]]]

Might not quite be what OP is asking for, but if you just need to quickly check if any migrations are pending for use in a rake task, without resorting to 

rake db:migrate:status | grep down (might not work if you're on Windows)

ActiveRecord::Migration.check_pending! (raises ActiveRecord::PendingMigrationError that you need to rescue)

you can use needs_migration? method: 
<a href="https://apidock.com/rails/v4.0.2/ActiveRecord/Migrator/needs_migration%3F/class" rel="nofollow noreferrer">https://apidock.com/rails/v4.0.2/ActiveRecord/Migrator/needs_migration%3F/class</a>

blocks|key|1250651|text|使用以下命令检查迁移状态：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1250652|rake+db:migrate:status|code-block|syntax|javascript|1250653|或|1250654|当您运行服务器时，它将显示一条消息，要求您先运行挂起的迁移。|1250655|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]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|6|7|P|8|@]|9|@]|A|$]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

Following command to check migration status:

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

OR

when you run your server, it will display a message to run your pending migration first.

Is there a rake task that shows the pending migrations in a rails app?

Show pending migrations in rails

在rails应用程序中有没有一个rake任务来显示挂起的迁移？

问在rails中显示挂起的迁移
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