Rails 4中的“ includes”方法似乎不适用于“ where” [英] 'includes' method doesn't seem to work with 'where' in Rails 4

问题描述

在我的模型中，我有：

class Song < ActiveRecord::Base

  belongs_to :artist

  def self.default_scope
    includes :artist
  end

  def self.search query
    if query
      where "title LIKE :query OR artists.name LIKE :query", query: "%#{ query }%"
    else
      where nil
    end
  end

end

在我的控制器中：

def index
  @songs = Song.search(params[:search])
  respond_with(@songs)
end

当我搜索时出现以下错误：

When I search I get the following error:

Mysql2::Error: Unknown column 'artists.name' in 'where clause': SELECT  `songs`.* FROM `songs` WHERE (title LIKE '%my search%' OR artists.name LIKE '%my search%' OR albums.name LIKE '%my search%')

我在做什么错了？，我认为include方法会自动进行连接。

What am I doing wrong?, I thought the includes method would make the join automatically.

推荐答案

来自文档：

使用其中仅当您将其传递给Hash时才起作用。对于
SQL片段，您需要使用引用强制联接表

Using where like this will only work when you pass it a Hash. For SQL-fragments you need use references to force joined tables

您是正确的， includes 方法将自动进行联接，但是当将散列用作<$ c $的参数时，仅 c>其中。

You are correct that the includes method will make the join automatically, but only when a hash is used as the argument to where.

这将检测查询并加入评论：

Article.includes(:comments).where(comments: { visible: true })

这需要明确的引用：

Article.includes(:comments).where("comments.visible = true").references(:comments)

不用担心 default_scope 是否是件好事，您可以使用以下代码运行代码：

Without getting into whether default_scope is a good thing or not, you could get your code running with this:

def self.search(query)
  if query
    references(:artists).
      where("title LIKE :query OR artists.name LIKE :query", query: "%#{query}%")
  else
    where nil
  end
end

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