fields_for form builder object is nil

Question

Any way to access a nested form_bulder.object?

## controller
@project = Project.new
@project.tasks.build

form_for(@project) do |f|
  f.object.nil? ## returns false

  fields_for :tasks do |builder|
    builder.object.nil? ## returns true
  end
end

score 72 · Accepted Answer · answered Mar 09 '10 at 16:45

72

You must have accepts_nested_attributes_for in the Project model in order for the object to be passed.

class Project < ActiveRecord::Base
  has_many :tasks
  accepts_nested_attributes_for :tasks ## this is required
end

answered Mar 09 '10 at 16:45

Chap

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Banged my head on this for about 90 minutes. Whew. – DanSingerman Mar 04 '16 at 16:28
1

About every 6 month i forget to add this, so annoying that there is no sensible error for this. But i guess it might be hard to detect automatically. – Ole Henrik Skogstrøm May 03 '16 at 12:43
Saved hours of my time - my gratitude is yours. Let this be a lesson to my team while doing some heavy refactoring/cleaning of some old and messy model. (ok...it was me,) – Yoopergeek Nov 23 '16 at 01:08

score 18 · Answer 2 · answered Jun 25 '14 at 10:39

fields_for requires that the method tasks_attributes= exists. accepts_nested_attributes_for :tasks creates this method for you, but you can also just define it yourself:

def tasks_attributes=(params)
  # ... manually apply attributes in params to tasks
end

When this method does not exist, the builder.object ends up being nil.

fields_for form builder object is nil

2 Answers2

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