如何在rails中的new.html.erb中查找和验证外键

Question

My data model is that a student is associated with a teacher. My student entry form will have a teacher username field, which I want to validate against an existing teacher record. How will I accomplish this in the app/view/student/new.html.erb file? Right now, I just have this:

<tr>
 <th>Teacher ID</th>
 <td><%= f.number_field :teacher_id %></td>
</tr>

I want to make this the :teacher_username and then validate against the teachers table. if a match is found, I want to get the teachers.id field and pass it on for insert into the student table. If a match is not found, then I want to flag an error that no such teacher username exists. How can I accomplish this. Any sample code would be helpful.

The student model file has belongs_to :teacher in it. The teacher model file has has_many :students in it.

Answer 1

As @Iceman suggested,a drop-down box is appropriate for your purpose.

In your /views/student/new.html.erb you can do this

<tr>
 <th>Select Teacher</th>
 <td><%= f.select :teacher_id,Teacher.all.collect {|t| [ t.teacher_username, t.id ] },{ include_blank: true } %></td>
</tr>

This will ensure that only the records that are present in teachers table will be available here in the drop-down and simplifies the validation part which you are looking.

Answer 2

I want to make this the :teacher_username and then validate against the teachers table. if a match is found, I want to get the teachers.id field and pass it on for insert into the student table. If a match is not found, then I want to flag an error that no such teacher username exists. How can I accomplish this. Any sample code would be helpful.

You may need to look at ActiveRecord validations

More specifically, I'd do somthing like this:

#app/models/teacher.rb
Class Teacher < ActiveRecord::Base
    vaidates :username, uniqueness: true
end

I mention "like" because you want to pass the details to your student table. If you're doing this with accepts_nested_attributes_for , then it's okay; however if you're not, then you may wish to divulge your process, so we can help you define it

--

Update

Having read your question more thoroughly, it seems you're trying to look up a teacher's username, then if it exists, pass the id back to the student table

A drop down will probably be the best option for this, however if you wanted to look up the name, you'd have to call an action on the students controller to validate the username via ajax, like:

#app/controllers/students_controller.rb
def check_teacher
    teacher = Teacher.find_by username: params[:userame]
end

But having read the question properly, I'd recommend the drop down