Adding a validation error in a controller in Rails 4

Question

In a controller I have a code which isn't associated with the model directly:

def create

  var1 = get_some_post_param
  # check if var1 isn't nil -- how to add an error the model if it is?

  # some other code...
  @m = Model.new(field1: var1, field2: var2, field3: var3)
  if @m.save
    # ok
    #....
  else
    # error
    ...
  end
end

How can I add a validation error to the model right after var1 = get_some_post_param if var1 is nil?

Answer 1

First of all, I don't think you can directly do that in your controller.

You can associate the non-model var1 attribute to any one of your model attribute (this can be a new attribute for this purpose, say: special_var1).

Then in your controller you can have:

  before_action :set_special_var1

  def set_special_var1
    var1 = get_some_post_param
    @m.special_var1 = var1
  end

And, then in your model, you can add a custom validator:

# model.rb
validate :special_var1_is_not_nil

private

def special_var1_is_not_nil
  if self.special_var1.nil?
    errors.add(:special_var1, 'special_var1 is nil')
  end
end

Or, you can also try:

validates :special_var1, allow_nil: false

However, these validations will be invoked before the object is being persisted e.g. when you call: @m.save, not before that.

Update

The best you can do in your controller is, having a before_action in your controller and then redirect to some page if var1 is nil:

before_action :check_var1

private

def check_var1
  var1 = get_some_post_param
  unless var1
    redirect_to "index", notice: "Invalid var1"
  end
end

See this post for some reference.