to_sql不起作用

Question

當我到to_sql以下查詢正常工作：

2.1.8 :017 > Task.joins(:recurrence).group('recurrences.id').to_sql 
=> "SELECT `tasks`.* FROM `tasks` INNER JOIN `recurrences` ON `recurrences`.`id` = `tasks`.`recurrence_id` GROUP BY recurrences.id" 

但後來當我添加pluck這是行不通的：

2.1.8 :018 > Task.joins(:recurrence).group('recurrences.id').pluck('tasks.title').to_sql 
    (21.0ms) SELECT tasks.title FROM `tasks` INNER JOIN `recurrences` ON `recurrences`.`id` = `tasks`.`recurrence_id` GROUP BY recurrences.id 
NoMethodError: undefined method `to_sql' for #<Array:0x007fbde9863f18> 

顯然，pluck的添加將對象的類型從ActiveRecord_Relation更改爲Array，並且您顯然無法在陣列上執行to_sql。

什麼我也想輸出（對於初學者）是這樣的：

SELECT tasks.title FROM `tasks` INNER JOIN `recurrences` ON `recurrences`.`id` = `tasks`.`recurrence_id` GROUP BY recurrences.id 

...這實際上是我複製/不通過to_sql產生Task.joins(:recurrence).group('recurrences.id').pluck('tasks.title')查詢粘貼。

是否有可能做我想做的事情？

Answer 1

我想通了。我必須使用select。

> Task.select('tasks.title').joins(:recurrence).group('recurrences.id').to_sql 
=> "SELECT tasks.title FROM `tasks` INNER JOIN `recurrences` ON `recurrences`.`id` = `tasks`.`recurrence_id` GROUP BY recurrences.id"