Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I'm going to echo what the other two have said. The survey you are trying to reference is <code>nil</code>, and <code>nil</code> does not have a method called <code>contact</code>. I am going to offer up a slightly different solution:</p> <pre><code>def create_permitted? acting_user == survey.try(:contact) or acting_user.administrator? end </code></pre> <p>The <code>#try</code> method exists on <code>nil</code> and on <code>survey</code>. It basically wraps the method call in a <code>rescue</code>. Conceptually, it looks like:</p> <pre><code>def try(method_name, *args) self.send(method_name, args) rescue nil end </code></pre> <p>This may reduce the amount of code that you have to write to catch conditions where a relationship may not be present, preventing a <code>NoMethodError</code> exception.</p> <p><code>#try</code> is part of the Rails core extensions for <code>Object</code>. In reality, it does not work as I have above, since exceptions arising from calls to <code>Object#try</code> will still happen as they normally should. Instead, it extends <code>Object</code> by calling <code>send</code>. It extends <code>NilClass</code> by returning <code>nil</code>, so it does not try to send any method to <code>NilClass</code>, preventing a <code>NoMethodError</code>. As tadman points out in the comments, a catch-all exception handler is normally not a good idea. </p> <p><a href="https://github.com/rails/rails/blob/6ef9fda1a39f45e2d18aba4881f60a19589a2c77/activesupport/lib/active_support/core_ext/object/try.rb" rel="nofollow">https://github.com/rails/rails/blob/6ef9fda1a39f45e2d18aba4881f60a19589a2c77/activesupport/lib/active_support/core_ext/object/try.rb</a></p> <p><strong>Update</strong></p> <p>A better solution, and one that I forgot about, is to use <code>delegate</code>.</p> <p>For example:</p> <pre><code>class User &lt; ActiveRecord::Base delegate :contact, to: :survey, prefix: true, allow_nil: true end </code></pre> <p>Then you would call <code>user.survey_contact</code>, and would fail gracefully if the survey is <code>nil</code>.</p>
    singulars
    1. This table or related slice is empty.
    1. POError: undefined method `contact' for nil:NilClass
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USSean Hill
    1. USSean Hill
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. CONice, the `try` method absolutely fits here.
      singulars
      1. PO
      1. USThomas Klemm
    2. COWriting a so-called [Pokemon Exception Handler](http://www.dodgycoder.net/2011/11/yoda-conditions-pokemon-exception.html) with `rescue nil` is a really bad idea and is a terrible form of defensive programming. This will consume legitimate problems with calling that method and will hide errors that would be trivial to fix with a proper stack trace. If you're expecting a `NoMethodError`, rescue that and *only* that.
      singulars
      1. PO
      1. UStadman
    3. COI'm not writing that so-called Pokemon Exception handler. It is part of Rails. It does not work like I described it; rather it defines try on Object and on NilClass, calling `send` on Object and returning `nil` on NilClass. Exceptions arising from `send` will still happen. I was only explaining conceptually how it works. https://github.com/rails/rails/blob/6ef9fda1a39f45e2d18aba4881f60a19589a2c77/activesupport/lib/active_support/core_ext/object/try.rb. Otherwise, I agree. Catching exceptions should be targeted at the specific exceptions.
      singulars
      1. PO
      1. USSean Hill
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload