问题
To my knowledge, the new default in Rails 5 requires belongs_to associations to be present. I made a model with this association, but the problem is I don't get presence validation error when the associated field is empty. Instead I get a database Null Validation error since I set the _id column not to be null. (PG::NotNullViolation because I use Postgres)
Is this behaviour normal? I mean shouldn't I get the rails error only?
BTW, when I add presence validation for the field, it works as I expected.
回答1:
According to the issue re weird behaviour of config belongs_to_required_by_default, it seems like one of your other gems intervenes in ActiveRecord::Base and causes the bug.
One of workarounds to the issue is to move the line
config.active_record.belongs_to_required_by_default = true
from initializers directly into application.rb.
This worked for me smoothly.
回答2:
New Rails 5 applications come with a new initializer in
config/initializers/active_record_belongs_to_required_by_default.rb
If you upgraded a Rails 4 application or created your application with a beta version of Rails 5, then that file might be missing.
The configuration in that file enables the feature in question:
# Be sure to restart your server when you modify this file.
# Require `belongs_to` associations by default. This is a new Rails 5.0
# default, so it is introduced as a configuration option to ensure that apps
# made on earlier versions of Rails are not affected when upgrading.
Rails.application.config.active_record.belongs_to_required_by_default = true
Please check how belongs_to_required_by_default is configured in your application.
回答3:
I faced with same problem.
You can move
config.active_record.belongs_to_required_by_default = false
to config/environments/needed_environment.rb or to config/application.rb
Helped for me!
来源：https://stackoverflow.com/questions/38157293/belongs-to-presence-in-rails-5-not-working