Ruby 在 rails - show.html.erb 中未定义的方法

Question

我正在尝试显示教师的姓名而不仅仅是 ID。

除我尝试显示教员姓名的那部分外，其他一切正常。我收到一条错误消息 "undefined method" 。

我知道我做错了什么，但我根本想不通，尽管我已经看了好几个小时了。我是一个完全的初学者，非常感谢您的帮助。

谢谢。

show.html.erb

<p id="notice"><%= notice %></p>
<!-- notice is a ruby method, and its results comes here inside the tags
used when you want the errow page to show on the next page -->
<p>
  <strong>Name:</strong>
  <%= @student.name %> 
</p>

<p>
  <strong>Faculty:</strong>
  <%= @student.faculty_id %>
  <%= @name.faculty_id %> 


</p>

 <strong>Grade:</strong>
  <%= @student.grade%>
</p>

<%= link_to 'Edit', edit_student_path(@student) %> |
<%= link_to 'Back', students_path %>

student.rb

class Student < ActiveRecord::Base
    belongs_to :faculty

end
class Name < ActiveRecord::Base
    belongs_to :faculty
end

faculty.rb

class Faculty < ActiveRecord::Base
    has_many :student
    # belongs_to :faculty
    has_many :name
end

这是我的 students_controler.rb

class StudentsController < ApplicationController
  before_action :set_student, only: [:show, :edit, :update, :destroy]

  # GET /students
  # GET /students.json
  def index
    @students = Student.all
  end

  # GET /students/1
  # GET /students/1.json
  def show
  end

  # GET /students/new
  def new
    @student = Student.new
  end

  # GET /students/1/edit
  def edit
  end

  # POST /students
  # POST /students.json
  def create
    @student = Student.new(student_params)

    respond_to do |format|
      if @student.save
        format.html { redirect_to @student, notice: 'Student was successfully created.' }
        format.json { render :show, status: :created, location: @student }
      else
        format.html { render :new }
        format.json { render json: @student.errors, status: :unprocessable_entity }
      end
    end
  end

  # PATCH/PUT /students/1
  # PATCH/PUT /students/1.json
  def update
    respond_to do |format|
      if @student.update(student_params)
        format.html { redirect_to @student, notice: 'Student was successfully updated.' }
        format.json { render :show, status: :ok, location: @student }
      else
        format.html { render :edit }
        format.json { render json: @student.errors, status: :unprocessable_entity }
      end
    end
  end

  # DELETE /students/1
  # DELETE /students/1.json
  def destroy
    @student.destroy
    respond_to do |format|
      format.html { redirect_to students_url, notice: 'Student was successfully destroyed.' }
      format.json { head :no_content }
    end
  end

  private
    # Use callbacks to share common setup or constraints between actions.
    def set_student
      @student = Student.find(params[:id])
    end

    # Never trust parameters from the scary internet, only allow the white list through.
    def student_params
      params.require(:student).permit(:name, :faculty_id)
    end
end

错误是 nil:NilClass

的未定义方法 `faculty_id'

Answer 1

<%= @name.faculty_id %> 不行。

在你的控制器中预先加载教员

def show
  @student = Student.includes(:faculty)
end

要么

<% if @student.faculty.present? %>
  <%= @student.faculty.name %>
<% end %>

或者您可以获取控制器中的 faculty 并将其分配给变量

def show
  @student = Student.includes(:faculty)
  @faculty = @student.faculty
end

那你就可以用那个了

<% if @faculty.present? %>
  <%= @faculty.name %>
<% end %>

Answer 2

我看到的错误是

class Faculty < ActiveRecord::Base
has_many :student
# belongs_to :faculty
has_many :name
end

应该是

class Faculty < ActiveRecord::Base
has_many :students
# belongs_to :faculty
has_many :names
end

我不知道你的错误是不是这样，但 has_many 不是单数形式

Answer 3

I am trying to display the name of the faculty instead of just the ID

既然你是初学者，那我就给你解释一下吧...

--

您正在呼叫 @student.faculty_id

这是 @student 对象的 foreign_key -- 将此 student 对象链接到适当的 faculty 对象的标识符。

简而言之，这意味着此属性是 student 架构的一部分——您需要一个属于 faculty 架构的一部分。因此，您要么需要使用 delegate 从 faculty 调用 name 属性，要么直接调用它：

@student.faculty.name

您的模型关联存在更深层次的问题。

The above 应该如何设置：

#app/models/student.rb
class Student < ActiveRecord::Base
   belongs_to :faculty
end

#app/models/faculty.rb
class Faculty < ActiveRecord::Base
   has_many :students
end

以上将允许您调用以下内容：

#app/controllers/students_controller.rb
class StudentsController < ApplicationController
   def show
      @student = Student.find params[:id]
   end
end

#app/views/students/view.html.erb
<%= @student.faculty.name %>

您必须记住 Rails 在 relational database 之上工作。这是通过允许您通过外键 .

调用相关对象来实现的

如果需要，我可以解释更多。

Ruby 在 rails - show.html.erb 中未定义的方法

Ruby on rails - undefined method in show.html.erb

methods

ruby-on-rails

undefined