blocks|key|2993982|text|:joins在sql中将表连接在一起，:includes+eager加载关联以避免n%2B1问题(执行一个查询来检索记录，然后为每个加载的关联执行一个查询)。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|2993983|我建议你阅读他们在Rails+Guides中的部分，以获得更多信息。|2993984|entityMap|0|LINK|mutability|MUTABLE|url|http://guides.rubyonrails.org/active_record_querying.html^0|0|6|J|9|0|9|C|0|0^^$0|@$1|2|3|4|5|6|7|P|8|@$9|Q|A|R|B|C]|$9|S|A|T|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|U|8|@]|D|@$9|V|A|W|1|X]]|E|$]]|$1|H|3|-4|5|6|7|Y|8|@]|D|@]|E|$]]]|I|$J|$5|K|L|M|E|$N|O]]]]

<code>:joins</code> joins tables together in sql, <code>:includes</code> eager loads associations to avoid the n+1 problem (where one query is executed to retrieve the record and then one per association which is loaded).

I suggest you read their sections in <a href="http://guides.rubyonrails.org/active_record_querying.html" rel="noreferrer">Rails Guides</a> to get more info.

blocks|key|3207555|text|stores+=+Store.joins(:car)|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|3207556|这将返回所有有汽车的商店。stores[0].car将导致另一个查询。|unstyled|offset|length|style|CODE|3207557|stores+=+Store.includes(:car)|3207558|这将返回所有商店，无论是否有车。stores[0].car不会导致另一个查询。|3207559|stores+=+Store.includes(:car).joins(:car)|3207560|这将返回具有汽车的所有商店。stores[0].car不会导致另一个查询。我不建议将其用于has_many关系，但它对has_one非常有效。|3207561|entityMap^0|0|D|D|0|0|G|D|0|0|E|D|19|8|1N|7|0^^$0|@$1|2|3|4|5|6|7|U|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|V|8|@$G|W|H|X|I|J]]|9|@]|A|$]]|$1|K|3|L|5|6|7|Y|8|@]|9|@]|A|$B|C]]|$1|M|3|N|5|F|7|Z|8|@$G|10|H|11|I|J]]|9|@]|A|$]]|$1|O|3|P|5|6|7|12|8|@]|9|@]|A|$B|C]]|$1|Q|3|R|5|F|7|13|8|@$G|14|H|15|I|J]|$G|16|H|17|I|J]|$G|18|H|19|I|J]]|9|@]|A|$]]|$1|S|3|-4|5|F|7|1A|8|@]|9|@]|A|$]]]|T|$]]

<pre><code>stores = Store.joins(:car)
</code></pre>

This will return all stores for which there is a car. <code>stores[0].car</code> will result in another query.

<pre><code>stores = Store.includes(:car)
</code></pre>

This will return all stores, car or no car. <code>stores[0].car</code> will not result in another query.

<pre><code>stores = Store.includes(:car).joins(:car)
</code></pre>

This will return all stores with a car. <code>stores[0].car</code> will not result in another query. I wouldn't recommend this for <code>has_many</code> relationships, but it works great for <code>has_one</code>.

blocks|key|3207538|text|:joins返回只读对象，:includes不返回|type|unstyled|depth|inlineStyleRanges|entityRanges|data|3207539|:joins使用内部联接，:includes使用外部联接。|3207540|includes的主要原因是急切加载，以避免使用单独的查询加载每个对象的属性的N%2B1问题。|3207541|entityMap^0|0|0|0^^$0|@$1|2|3|4|5|6|7|H|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|I|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|J|8|@]|9|@]|A|$]]|$1|F|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|G|$]]

:joins returns read-only objects, :includes does not

:joins uses inner join, :includes uses outer join.

the main reason of :includes is eager loading, to avoid the N+1 problem of loading in attributes of each object using a separate query.

blocks|key|282271|text|join将只连接表，并返回选定的字段。如果对连接查询结果调用关联，它将再次触发数据库查询|type|unstyled|depth|inlineStyleRanges|entityRanges|data|282272|Include将立即加载包含的关联，并将它们添加到内存中。Include加载所有包含的表属性。如果对include查询结果调用关联，则不会触发任何查询|282273|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Joins will just join the tables and brings selected fields in return. if you call associations on joins query result, it will fire database queries again
Include will eager load the included associations and add them in memory. Include loads all the included tables attributes. If you call associations on include query result, it wont fire any queries

blocks|key|2994048|text|TL；DR|type|unstyled|depth|inlineStyleRanges|entityRanges|data|2994049|加入：|2994050|a.joins(:b).to_sql
=>+"SELECT+\"a\".*+FROM+\"a\"+INNER+JOIN+\"b\"+ON+\"b\".\"id\"+=+\"a\".\"b_id\""|code-block|syntax|javascript|2994051|包括：|2994052|a.includes(:b).to_sql
=>+"SELECT+\"a\".*+FROM+\"a\"|2994053|两者：|2994054|a.includes(:b).joins(:b).to_sql
=>+"SELECT+\"a\".\"id\"+AS+t0_r0,+\"a\".\"a_field_1\"+AS+t0_r1,+\"a\".\"a_field_2\"+AS+t0_r2,+\"a\".\"a_field_3\"+AS+t0_r3,+\"b\".\"a_field_1\"+AS+t1_r1,+\"b\".\"a_field_2\"+AS+t1_r2,+\"b\".\"a_field_3\"+AS+t1_r3+FROM+\"a\"+INNER+JOIN+\"b\"+ON+\"b\".\"id\"+=+\"a\".\"plan_id\""|2994055|entityMap^0|0|0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|S|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|T|8|@]|9|@]|A|$]]|$1|D|3|E|5|F|7|U|8|@]|9|@]|A|$G|H]]|$1|I|3|J|5|6|7|V|8|@]|9|@]|A|$]]|$1|K|3|L|5|F|7|W|8|@]|9|@]|A|$G|H]]|$1|M|3|N|5|6|7|X|8|@]|9|@]|A|$]]|$1|O|3|P|5|F|7|Y|8|@]|9|@]|A|$G|H]]|$1|Q|3|-4|5|6|7|Z|8|@]|9|@]|A|$]]]|R|$]]

TL; DR

Joins:

<pre><code>a.joins(:b).to_sql
=&gt; "SELECT \"a\".* FROM \"a\" INNER JOIN \"b\" ON \"b\".\"id\" = \"a\".\"b_id\""
</code></pre>

Includes:

<pre><code>a.includes(:b).to_sql
=&gt; "SELECT \"a\".* FROM \"a\"
</code></pre>

Both:

<pre><code>a.includes(:b).joins(:b).to_sql
=&gt; "SELECT \"a\".\"id\" AS t0_r0, \"a\".\"a_field_1\" AS t0_r1, \"a\".\"a_field_2\" AS t0_r2, \"a\".\"a_field_3\" AS t0_r3, \"b\".\"a_field_1\" AS t1_r1, \"b\".\"a_field_2\" AS t1_r2, \"b\".\"a_field_3\" AS t1_r3 FROM \"a\" INNER JOIN \"b\" ON \"b\".\"id\" = \"a\".\"plan_id\""
</code></pre>

blocks|key|285893|text|:joins是JOINS的ActiveRecord版本。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|285894|Store.joins(:car).to_sql
=>+SELECT+stores.*+FROM+stores+INNER+JOIN+cars+ON+cars.store_id+=+categories.id|code-block|syntax|javascript|285895|因此，在So的背后是一个隐含的INNER+JOIN。因此，它确实会返回所有拥有汽车的商店(因为有了inner_join，left_outer_join就会有不同的行为)。请参阅更多here。|285896|而:includes不是查询命令。它通过在商店模型上eager_loading汽车模型来解决n%2B1查询问题。查看更多eager_loading+here。|285897|stores+=+Store.includes(:car)|285898|因此将返回所有存储，并允许在不触发新查询的情况下执行stores.first.car。|285899|entityMap|0|LINK|mutability|MUTABLE|url|https://guides.rubyonrails.org/v5.2/active_record_querying.html#joins|1|https://apidock.com/rails/ActiveRecord/QueryMethods/includes^0|0|6|0|0|F|A|1D|A|1O|F|2I|4|0|0|1|9|Q|D|1M|D|20|4|1|0|0|Q|G|0^^$0|@$1|2|3|4|5|6|7|12|8|@$9|13|A|14|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|15|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|16|8|@$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]]|D|@$9|1D|A|1E|1|1F]]|E|$]]|$1|M|3|N|5|6|7|1G|8|@$9|1H|A|1I|B|C]|$9|1J|A|1K|B|C]|$9|1L|A|1M|B|C]]|D|@$9|1N|A|1O|1|1P]]|E|$]]|$1|O|3|P|5|H|7|1Q|8|@]|D|@]|E|$I|J]]|$1|Q|3|R|5|6|7|1R|8|@$9|1S|A|1T|B|C]]|D|@]|E|$]]|$1|S|3|-4|5|6|7|1U|8|@]|D|@]|E|$]]]|T|$U|$5|V|W|X|E|$Y|Z]]|10|$5|V|W|X|E|$Y|11]]]]

<code>:joins</code> is the ActiveRecord version of JOINS, the SQL request.

<pre><code>Store.joins(:car).to_sql
=&gt; SELECT stores.* FROM stores INNER JOIN cars ON cars.store_id = categories.id
</code></pre>

So behind the seen it is an implicit <code>INNER JOIN</code>. It will thus indeed return all stores that have a car (because of the <code>inner_join</code>, a <code>left_outer_join</code> would have had a different behaviour). See more <a href="https://guides.rubyonrails.org/v5.2/active_record_querying.html#joins" rel="nofollow noreferrer">here</a>.

Whereas <code>:includes</code> is not a query command. It solves the n+1 query issue by <code>eager_loading</code> the Car model on the Store model. See more one <code>eager_loading</code> <a href="https://apidock.com/rails/ActiveRecord/QueryMethods/includes" rel="nofollow noreferrer">here</a>.

<pre><code>stores = Store.includes(:car)
</code></pre>

will thus return all stores, and allows to do <code>stores.first.car</code> without firing a new query.

blocks|key|283854|text|Join:它使用延迟加载，并执行内部连接。joins简单地将两个表添加到一起|type|unstyled|depth|inlineStyleRanges|entityRanges|data|283855|Includes:+Includes使用预加载并执行左外部联接，includes还可以防止N%2B1查询。|283856|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|F|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|G|8|@]|9|@]|A|$]]|$1|D|3|-4|5|6|7|H|8|@]|9|@]|A|$]]]|E|$]]

Join: It uses lazy loading and it performs an inner join. joins to simply add two tables together
Includes: Includes uses eager loading and perform a left outer join and includes can also prevent the N+1 queries.

What's the difference between "includes" and "joins" in ActiveRecord query? Can anyone explain to me with the following two associated models?

<pre><code>class Car &lt; ActiveRecord::Base
 belongs_to :store
end

class Store &lt; ActiveRecord::Base
 belongs_to :owner
 has_one :car
end
</code></pre>

What's the difference between "includes" and "joins" in ActiveRecord query?

"includes“和"joins”在ActiveRecord查询中有什么区别？谁能给我解释一下下面两个相关的模型？class Car < ActiveRecord::Base belongs_to :storeendclass Store < ActiveRecord::Base belongs_to :owner has_one :carend

问ActiveRecord查询中的"includes“和"joins”有什么区别？
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问ActiveRecord查询中的"includes“和"joins”有什么区别？EN

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问ActiveRecord查询中的"includes“和"joins”有什么区别？
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