undefined method for nil:NilClass

Question

I'm getting the following error. I know the reason is that I'm calling a function on a related record that hasn't been related yet, but didn't know the best way to fix this.

Code causing the error:

<%= link_to member.names.last.fullname, polymorphic_path([member, Name]) %>

In this example Name has a belongs_to relationship with Member and Member has a has_many relationship with Name. It happens to be a polymorphic relationship, but I don't think that matters for this error.

When the above code is called and there are no related Names the error is:

undefined method `fullname' for nil:NilClass

I'm sure there is something very basic I'm missing here that should prevent this from happenning. Thanks in advance for any help that you all can offer!

Mark

More Code:

class Name < ActiveRecord::Base
belongs_to :person, polymorphic: true

attr_accessible :dob, :dod, :first, :gender, :last, :mi, :prefix, :relation, :suffix

def fullname
first + last
end
end


class Member < ActiveRecord::Base
has_many :names, as: :person

attr_accessible :active, :deleted
end

The member in question doesn't have any names associated with it yet. Add a default name or check to see if you have any names prior to asking for last — ilan berci

Damien MATHIEU Damien MATHIEU · Accepted Answer · 2013-07-23T15:15:45

The quick way to solve this would be to use #try.

<%= link_to member.names.last.try(:fullname), polymorphic_path([member, Name]) %>

This will fix the error. However, it will display a link without any value.
Therefore, you need to provide a default fullname value to your member.

One solution for this is to add a fullname method to your Member model.

class Member < ActiveRecord::Base
  def fullname
    if names.any?
      names.last.fullname
    else
      "John Doe"
    end
  end
end

Then, in your view, you just have to do :

<%= link_to member.fullname, polymorphic_path([member, Name]) %>

If the member does not have any name defined, you fallback to a default. Here, it is "John Doe". But set it to whatever you want.

An other solution is to just force the member to have at least one name.

class Member < ActiveRecord::Base
  has_many :names, as: :person
  validates :names, presence: true
end

Your member will have validation errors and won't me able to be saved, unless he specifies at least one name.
Using this, you'll also need to use nested attributes, to allow the member to effectively add his name when creating itself, not after.

undefined method for nil:NilClass

1 Answers