rails left join
That would be a left join where the user id is null or matches. books = Book .left_outer_join(:readings) .where(readings: user_id: [nil, current_user.id] }). , You can pass a string that is the join-sql too. eg joins("LEFT JOIN StudentEnrollment se ON c.id = se.course_id"). Though I'd use rails-standard ...
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 rails left join 相關參考資料
Active Record 查詢— Ruby on Rails 指南
Ruby on Rails 指南：系統學習Rails（Rails 4.2 版本） ... 產生的查詢語句會有 LEFT OUTER JOIN ，而 joins 產生的是 INNER JOIN 。 https://rails.ruby.tw How to use left joins in Rails : rails - Reddit
That would be a left join where the user id is null or matches. books = Book .left_outer_join(:readings) .where(readings: user_id: [nil, current_user.id] }). https://www.reddit.com LEFT OUTER JOIN in Rails 4 - Stack Overflow
You can pass a string that is the join-sql too. eg joins("LEFT JOIN StudentEnrollment se ON c.id = se.course_id"). Though I'd use rails-standard ... https://stackoverflow.com rails 5 left outer join - Stack Overflow
LEFT JOIN: The LEFT JOIN returns all rows from the left table, even if there are no matches in the right table. This means that if the ON clause ... https://stackoverflow.com Rails left join conditional - Stack Overflow
Try this: Item.includes(:orders).where.not(orders: status: [1,2,3]}). You can check the generated SQL using to_sql. EDIT. To include items which do have an order ... https://stackoverflow.com Rails: joins的使用. 在Rails專案中常常需要撈關聯的資料，或者 ...
在Rails專案中常常需要撈關聯的資料，或者是用關聯資料的欄位當成判斷條件來撈需要的資料。ActiveRecord的joins方法將SQL的INNER JOIN ... https://medium.com Ruby on Rails - 用Include 和Join 避免N+1 Query - Leon's ...
在rails 當中，因為ORM (Object-relational mapping ) 的便利，可以很快速地 ... 再透過欄位去做篩選; joins 為inner join ， include 為left outer join ... https://mgleon08.github.io Support for left outer join in Rails 5 | BigBinary Blog
In Rails 4.x, we need to write the SQL for left outer join manually as Active Record does not have support for outer joins. authors ... https://blog.bigbinary.com [Rails 效能優化] 資料庫關聯查詢. 你以為只懂includes 就夠了嗎 ...
eager_load 使用SQL 的 LEFT OUTER JOIN 方法，查詢的時候只會產生一個語句，直接加載所有的關聯數據。如果我們使用 includes 用了進階 ... https://medium.com |