Ruby on Rails:两种模型之间的关系 [英] Ruby on Rails: Relation between two models

问题描述

我正在挑战自己建立一个小的市场，以便您可以在类别中发布请求".为此，我既有请求模型又有类别模型.如何在这些模型之间添加关系，以使Category知道它属于请求，反之亦然?我已经做到了:

I am challenging myself to build a little marketplace where you will be able to post a "request" inside a category. For that I have both the request model and the category model. How can I add a relation between those models, so that the Category knows that it belongs to a request and vice versa? I already did:

category.rb

has_and_belongs_to_many :requests 

request.rb

has_one :category

现在在我的表单部分中，我有以下代码:

Now inside my form partial I have this code:

<%= f.select :category, Category.all, :prompt => "Kategorie", class: "form-control" %>

奇怪的是，:category不存在，因为该列应为:name.在我的seeds.rb中，插入了以下内容，该内容在rake db:seed

The strange thing is :category does not exist, as the column should be :name. In my seeds.rb I've inserted the following, which runs fine after rake db:seed

Category.create(name: 'PHP')

Category.create(name: 'Ruby')

Category.create(name: 'HTML')

Category.create(name: 'ASP')

Category.create(name: 'C#')

Category.create(name: 'C++')

但是上面带有:category的代码显示了这一点:

But the above code with :category shows this:

种子文件中共有6个类别，但没有类别的实际名称(例如"PHP").如果我在这段代码中使用:name而不是:category:

There are all 6 Categories from the seed file, but not the actual name of the category (like "PHP"). If i'm taking :name instead of :category in this code:

<%= f.select :category, Category.all, :prompt => "Kategorie", class: "form-control" %>

我得到

undefined method `name' for #<Request:0x007ff504266b40>

我的类别表:

Category(id: integer, name: string, description: text, created_at: datetime, updated_at: datetime)

保存后，如何命名特定请求的类别? @Category.request?

How can I call the category for a specific request, when it's saved? @Category.request?

我真的很困惑(对不起，我仅从8月下旬开始学习Rails).

I'm really confused (sorry I'm learning Rails only since late August).

非常感谢！

推荐答案

如果我正确理解它，例如在一个请求属于一个类别，而一个类别可以有多个请求，则应该这样建立关联:

If I understand it correctly, as in one Request belongs to one category and one category can have multiple requests the associations should be set up like this:

class Request < ActiveRecord::Base
  belongs_to :category
end

class Category < ActiveRecord::Base
  has_many :requests
end

像这样，请求表中的条目将具有类别的外键category_id.

Like this the entries in request table will have the foreign key category_id to the category.

您还可以在活动记录关联指南

You can also read a lot about association basics in the Active Record Associations Guide

保存后，如何命名特定请求的类别? @ Category.request吗?

How can I call the category for a specific request, when it's saved? @Category.request ?

要获取特定请求的类别，您必须从该请求开始，例如:

To get the category for a specifc request you have to start from the request for example like this:

@request = Request.first
@reqest.category

在表单中，如果要使用select标签，则可能必须使用category_id:

In your form you probably then have to use category_id if you want to use the select tag like this:

<%= f.select :category_id, Category.all.map { |c| [c.name, c.id] }, :prompt => "Kategorie", class: "form-control" %>

地图将确保您选择的地图将使用标签的名称和ID的值.

The map will make sure that it will use the name for the label and the id for the value in your select.

要使关联和其他内容的生成表单更容易，您还可以查看gem simple_form .然后，您只需使用:

To make generating forms for associations and other stuff easier you can also have a look at the gem simple_form. Then all you have to use is:

<%= f.association :category %>

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