Rails 4-链接模型关联以访问关联的方法

Question

I have models for User, Profile and Organisation Request. The associations are:

User

has_one :profile, dependent: :destroy
has_one :organisation_request, through: :profile 
    accepts_nested_attributes_for :organisation_request

Profile

belongs_to :user
belongs_to :organisation

Organisation Request

belongs_to :profile
# belongs_to :user#, through: :profile  
belongs_to :organisation

In my user model, I have a method called full_name (which I use to format the presentation of a user's name.

I'm trying to access that full_name method in my organisation_requests model.

I'm trying to do that by writing the following method in my organisation requests model:

def related_user_name
    self.profile.user.full_name
end

When I try to use this in my organisation requests index, like this:

          <%= link_to orgReq.related_user_name, organisation_request.profile_path(organisation_request.profile.id) %>

I get an error that says:

undefined method `user' for nil:NilClass

When I try to use this idea in the rails console, with:

o = OrganisationRequest.last

  OrganisationRequest Load (0.4ms)  SELECT  "organisation_requests".* FROM "organisation_requests"  ORDER BY "organisation_requests"."id" DESC LIMIT 1
 => #<OrganisationRequest id: 2, profile_id: 1, organisation_id: 1, created_at: "2016-08-01 22:48:52", updated_at: "2016-08-01 22:48:52"> 
2.3.0p0 :016 > o.profile.user.formal_name
  Profile Load (0.5ms)  SELECT  "profiles".* FROM "profiles" WHERE "profiles"."id" = $1 LIMIT 1  [["id", 1]]
  User Load (0.5ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = $1 LIMIT 1  [["id", 1]]
 => " John Test" 

The concept seems to work in the console? Can anyone see where I've gone wrong?

Answer 1

Don't chain methods, it's a bad practice, it violates the Law of Demeter . The best choice is to use the delegate . So instead of:

def related_user_name
  self.profile.user.full_name
end

You can have:

class OrganisationRequest
  belongs_to :profile
  has_one :user, through: :profile

  delegate :full_name, to: :user, allow_nil: true, prefix: true
end

Then you can just call organisation_request.user_full_name and it will go through profile > user and call full_name (and you won't get undefined since the allow_nil: true will "cover" it)

More info about delegate here .

Answer 2

have you checked all of your organisation requests have profile? may be this is not best practice, try to use profile.try(:user).try(:full_name)