Rails-将联接与自定义名称关联一起使用 [英] Rails - Using join with custom-named associations

问题描述

我有以下模型

class Measurement < ApplicationRecord
  belongs_to :examination, class_name: "TestStructure", foreign_key: "examination_id"

end

该关联实际上是与TestStructure模型建立的，但是关联名称是检查。 没有检查表。

The association is actually made to the TestStructure model, but the association name is examination. There is no examination table.

当我使用 join 。以下查询

Measurement.joins(:examination).where(examination: { year: 2016, month: 5 })

失败，出现此错误

ActiveRecord::StatementInvalid:
   PG::UndefinedTable: ERROR:  missing FROM-clause entry for table "examination"
   LINE 1: ...d" = "measurements"."examination_id" WHERE "examinati...
# --- Caused by: ---
 # PG::UndefinedTable:
 #   ERROR:  missing FROM-clause entry for table "examination"
 #   LINE 1: ...d" = "measurements"."examination_id" WHERE "examinati...

很明显，考试表不存在，但是我找不到一种方法告诉ActiveRecord我使用的是命名关联而不是

So clearly, the examinations table doesn't exists, but I can't find a way to tell ActiveRecord I'm using a named association instead of the default one.

有什么见解？

推荐答案

其中需要实际的表名，只需将其插入SQL中即可。

where expects the actual table name, it just inserts it in SQL:

Article.where(whatever: {you: 'want'}).to_sql
=> "SELECT `articles`.* FROM `articles` WHERE `whatever`.`you` = 'want'"

因此，您可以使用：

Measurement.joins(:examination).where(test_structures: { year: 2016, month: 5 })

但这不是很好

然后，您依赖表名称，而Model应该抽象这些内容。您可以使用 merge ：

Then you depend on table name while Model should abstract such things. You could use merge:

Measurement.joins(:examination).merge(TestStructure.where(year: 2016, month: 5))

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