undefined method for ActiveRecord::Relation

Question

User model

class User < ActiveRecord::Base
  has_many :medicalhistory 
end

Mdedicalhistory model

class Medicalhistory < ActiveRecord::Base
  belongs_to :user #foreign key -> user_id
  accepts_nested_attributes_for :user
end

Error

undefined method `lastname' for #<ActiveRecord::Relation:0xb6ad89d0>


#this works
@medicalhistory = Medicalhistory.find(current_user.id) 
print   "\n" + @medicalhistory.lastname

#this doesn't!
@medicalhistory = Medicalhistory.where("user_id = ?", current_user.id)
print   "\n" + @medicalhistory.lastname #error on this line

not sure if this is "best practice", but @medicalhistory = Medicalhistory.where("user_id = ?", current_user.id)[0] should work — Straff
– Straff, Commented May 5, 2013 at 10:27
as a noob, using find instead of where fixed the issues for me — wruckie
– wruckie, Commented Feb 24, 2023 at 15:42

Zabba · Accepted Answer · 2011-05-14 21:41:26Z

46

Well, you are getting back an object of ActiveRecord::Relation, not your model instance, thus the error since there is no method called lastname in ActiveRecord::Relation.

Doing @medicalhistory.first.lastname works because @medicalhistory.first is returning the first instance of the model that was found by the where.

Also, you can print out @medicalhistory.class for both the working and "erroring" code and see how they are different.

answered May 14, 2011 at 21:41

Zabba

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1 Comment

Smar Over a year ago

Thanks, I missed first method when looking at the API.

Thomas · Accepted Answer · 2013-11-06 20:22:17Z

One other thing to note, :medicalhistory should be plural as it is a has_many relationship

So your code:

class User < ActiveRecord::Base
  has_many :medicalhistory 
end

Should be written:

class User < ActiveRecord::Base
  has_many :medicalhistories 
end

From the Rails docs (found here)

The name of the other model is pluralized when declaring a has_many association.

This is because rails automatically infers the class name from the association name.

If a user only had_one medicalhistory this would be singular as you had written:

class User < ActiveRecord::Base
  has_one :medicalhistory 
end

I know you already accepted an answer, but thought this would help reduce further errors/confusion.

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