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First the environment:

Rails 2.1.0, Ruby 1.8.7, Mysql 5.1.54, Ubuntu 11.04

I have a boolean field in my table which starts as NULL, but I can not find a good way to set it to NULL. (This field is basically a yes / no / unanswered field, which true / false / null seems about right for. The client specifically said he would like it to be able to remain null (unanswered).)

Here is my migration (specific names replaced):

class AddQuestionToClients < ActiveRecord::Migration
    def self.up
        add_column :clients, :question, :boolean
    end
    def self.down
        remove_column :clients, :question
    end
end

My controller uses a basic

@client = Client.find(params[:id])
@client.update_attributes(params[:client])

My view has a select (I think this is causing the problem, was never great with form helper selects):

<%= f.select :question, [["Yes", true], ["No", false]], { :include_blank => true, :selected => @client.question } %>

When selecting yes, true is passed; no, false is passed; blank, "" is passed. But "" seems to automatically convert to false when updating the database.

To get around this, I'm doing this:

params[:client][:question] = (params[:client][:question] == "")? nil : params[:client][:question]

But this can't be the right way to do it. What am I missing?

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1
  • In the end, I decided to just use an integer and enum_fu, so 0=Unknown, 1=No 2=Yes. This seems the best solution to this specific problem, but the broader question is really "How do you use a Boolean with null", which I think Fabio answered pretty well. Commented Aug 17, 2011 at 23:38

6 Answers 6

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2

I think that you can do that only in that way server side, because when a data is posted is always not nil. So your solution is correct.

If you want to avoid that ugly code you can do a little trick client side using javascript. In fact if you use a disabled element instead of a blank value that value won't be posted and you get nil on server side.

To do that you can add a submit callback that checks whether the question field is blank and if so disable it before posting data. In that way it will work without any server side code.

To disable an element using jQuery you can see this link. So assuming your form has the #form id you can use this code

$(function() {
  $('#form').submit(function () {
    if ($('question-selector').val() == "") {
      $('question-selector').attr('disabled', true);
    }
  })
});
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4 Comments

I think just validating server side the way I am is less complicated and more straightforward than using javascript; thanks for the alternative idea though!
@d3vkit you still need server side validation, my trick is to remove the empty string from the params hash, because when you send some data with a post request it's always a string, it can't be nil. So js code is an alternative to your controller check, but the remaining part of your code (both controller and model) must remain untouched.
So, maybe I'm still being thick-headed, but you remove the param entirely and then re-add it in the controller if it doesn't exist (assuming that it was meant to be nil?) Would the benefit be if you needed to actually send a blank string param over? In this case it just seems like extra work for the client, with no less work for the server, unless I misunderstood. However, your point of "post data is always a string that can't be nil" answers this question, I think. Thanks!
@d3vkit just to be clear js remove the param only if it's blank. You don't need to add it again in your controller because if it's removed the corresponding field won't be set by update_attributes call. So if you select a value that value will populate the model attribute, otherwise the field will contain nil (i.e. NULL in SQL language)
2

I just ran into the same problem, and I solved it by making the attribute convert blank to null. In your case, I would add a method to your model class.

class Client < ActiveRecord::Base
  def question=(value)
    value = nil if value == ''
    super(value)
  end
end

This works for both create and update. (I'm using Rails 2.0.5.)

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1

I had the same problem, i needed null value by default for boolean to represent "not answered"

With Rails 3.2, when i pass "" for a boolean value (blank option) is sets the column to NULL in db.

So problem solved with newer version of rails :)

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0 
<%= f.select :question, options_for_select([["Yes", true], ["No", false]], :question) %>
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@vdaubry I would only add that it is not really solved ..it is masked because you are using 'select' in your UI. If you are foolish enough to use checkboxes, like me (after all, they are booleans, right?) then your nice default nil value in the db, which we mean to represent 'unknown' is converted to 'false' when rendered in the view, and converted to false in the db, even when it is not updated in the view, same as was described above. In other words, it's a bit brittle to continue to rely on a 3rd value for 'boolean' being consistent.

Furthermore, if ever reporting on this attribute, your reporting code cannot easily deduce the values in the db, if "unknown" is a valid meaning and is obscured.

So I chose to refactor all my booleans making them strings ('yes', 'no', 'unknown') and use radio buttons in the views. Note this only matters for things like data collection UIs, where a user has not got round to finding out the truth, so statistically it matters a lot if it's "unknown".

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7 Comments

Was this using the rails check_box? It renders a hidden checkbox with a value of 0, which would indeed translate to a save of 'false' in the db. check_box_tag doesn't do this, and "The HTML specification says unchecked check boxes are not successful, and thus web browsers do not send them", so they wouldn't be updated.
I used the form helper, f.checkbox. Is that the same as 'checkbox'? It seems to behave the same -- upon inspecting the html in the browser, I do see the hidden field with a value of "0".
Yah, f.check_box is the same as check_box. If you look at the format: check_box(object_name, method, options = {}, checked_value = "1", unchecked_value = "0"), the form builder object (f) is replacing object_name.
So the bottomline is, different controls in the view will result in different model data (if trying to rely on 'nil' to mean 'unknown', or 'not answered'). Which seems dicey. I'd rather have not have that dependence (on using one or another control) to get reliable model data.
Well, the problem isn't with Rails form builders; it's all working exactly as it should. The check_box will always make a hidden value of 0 for that field, so when it's submitted, the model will update to reflect that submission. check_box_tag will not make this hidden value though, so would not update the model. However, using a checkbox for 3 values is probably a bad idea, since it's harder to tell what the actual state of the field is, for the user.
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0

This isn't mentioned in previous posts, but in Rails 5 this should work if you want to name the nil option

<%= f.select :question, [["Yes", true], ["No", false]], { :include_blank => 'Name this whatever you want, it will be nil when submitted', :selected => @client.question } %>

Tested this on my own project

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