从多个表中检索过滤数据

https://guides.rubyonrails.org/active_record_querying.html

从多个表中检索过滤数据

Customer<br />
&nbsp; .select(&#39;customers.id, customers.last_name, reviews.body&#39;)<br />
&nbsp; .joins(:reviews)<br />
&nbsp; .where(&#39;reviews.created_at &gt; ?&#39;, 1.week.ago)

查询语句执行的结果是这样的：

SELECT customers.id, customers.last_name, reviews.body<br />
FROM customers<br />
INNER JOIN reviews<br />
&nbsp; ON reviews.customer_id = customers.id<br />
WHERE (reviews.created_at &gt; &#39;2019-01-08&#39;)

从多个表中检索特定数据

Book<br />
&nbsp; .select(&#39;books.id, books.title, authors.first_name&#39;)<br />
&nbsp; .joins(:author)<br />
&nbsp; .find_by(title: &#39;Abstraction and Specification in Program Development&#39;)

查询结果：

SELECT books.id, books.title, authors.first_name<br />
FROM books<br />
INNER JOIN authors<br />
&nbsp; ON authors.id = books.author_id<br />
WHERE books.title = $1 [[&quot;title&quot;, &quot;Abstraction and Specification in Program Development&quot;]]<br />
LIMIT 1