Collect all values for a given column in an ActiveRecord scope
The Edge Rider gem allows you to collect an array of values for one field of your ActiveRecord elements:
>> User.active.collect_column(:id)
=> [1, 5, 23, 42]
It also comes with a :distinct option in case you are only interested in unique values:
>> Article.collect_column(:state, distinct: true)
=> ['draft', 'published']
In modern Railses (since 3.2) you can also use ActiveRecord's pluck met…
Nested ActiveRecord transaction pitfalls
When working with custom transactions you may encounter unexpected behaviour if you try to roll back your changes.
tl;dr
Not all databases support nested transactions. Therefore, Rails will sometimes silently ignore a nested transaction and simply reuse the other transaction. However, a ActiveRecord::Rollback within the nested transaction will be caught by the block of the nested transaction, but will be ignored by the outer transaction, and not cause a roll back!
To avoid this unexpected behaviour, you have to explicitly tell rai…
Hints for debugging MySQL InnoDB deadlocks
Deadlocks only occur if two transactions in separate threads compete for the same rows in the database. They usually (but not necessarily) only happen when trying to update or otherwise lock several rows in different order.
Solving deadlocks is potentially complicated, so here are a few pointers:
- MySQL should always detect the deadlock right when it happens, and will throw an error to one of the offending threads. This error states the SQL statement that this thread was currently waiting for, and that tried to acquire one of the competin…
Rails: How to use prepend to avoid monkey patches in modules
Let's say you have a gem which has the following module:
module SuperClient
def self.foo
'Foo'
end
def bar
'Bar'
end
end
For reasons you need to override foo and bar.
Keep in mind: Your code quality is getting worse with with each prepend (other developers are not happy to find many library extensions). Try to avoid it if possible.
- Add a
lib/ext/super_client.rbto your project (Folder or file needs to be required in an initializer) - Add the extension, which overrides both methods (prepend i…
How to write a good changelog
We want to keep a changelog for all gems we maintain. There are some good practices for writing a changelog that adds value, please stick to these.
- Add a notice to the README's contribute section about the changelog
- For every release update the changelog
- Note the date format yyyy-mm-tt
What is a changelog?
A changelog is a file which contains a curated, chronologically ordered list of notable changes for each version of a project.
Why keep a changelog?
To make it easier for users and…
How to make changes to a Ruby gem (as a Rails developer)
At makandra, we've built a few gems over the years. Some of these are quite popular: spreewald (475k downloads), active_type (330k downloads), and geordi (210k downloads) for example (numbers from 2018).
Developing a Ruby gem is different from developing Rails applications, with the biggest difference: there is no Rails. This means:
- no defined structure (neither for code nor directories)
- no autoloading of classes, i.e. you need to
requireall files yourself - no [
active_support](https://api.rubyonrails.org/classes/ActiveSupport.ht…
HTML forms with multiple submit buttons
Most forms have a single submit button that will save the record when pressed.
Sometimes a form needs additional submit buttons like "accept" or "reject". Such buttons usually attempt a state transition while updating the record.
To process a form with multiple buttons, your server-side code will need to know which button was pressed. To do so you can give each submit button a different [formaction] attribute. This will override the …
Project management best practices: Project team responsibilities
In a project team for a bigger project people have several roles:
- Developer: at makandra
- Project lead: at makandra
- Project manager (PM): at makandra, external, or with the customer. In a smaller project this person is also the project lead.
- Product owner (PO): with the customer
Developer
- Development
- Take responsibility for their stories. This includes always gathering all necessary information from the project lead or the PM, communicate blockers, make sure stories are merged, deployed etc.
- Tell the project lead, if you'r…
Best practices: Large data migrations from legacy systems
Migrating data from a legacy into a new system can be a surprisingly large undertaking. We have done this a few times. While there are significant differences from project to project, we do have a list of general suggestions.
Before you start, talk to someone who has done it before, and read the following hints:
Understand the old system
Before any technical considerations, you need to understand the old system as best as possible. If feasible, do not only look at its API, or database, or frontend, but let a user of the old system sho…
PostgreSQL and its way of sorting strings
PostgreSQL uses the C library's locale facilities for sorting strings:
- First, all the letters are compared, ignoring spaces and punctuation.
- Then, spaces and punctuation are compared to break ties.
- It sorts upper and lower case letters together. So the order will be something like a A b B c C
Example:
| Ruby | PostgreSQL |
|---|---|
| IMAGE3.jpg | image2.jpg |
| image.jpg | image3.jpg |
| image2.jpg | IMAGE3.jpg |
| image3.jpg | image.jpg |
[PostgreSQL-FAQ: Why_do_my_strings_sort_incorrectly](https://wiki.postgresql.org/wiki…
AppArmor in Linux
This note is a reminder that there is something called AppArmor that could cause weird errors ("File not found", "Can't open file or directory", …) after configuration changes, e.g. when changing MySQL's data directory.
Remember to have a look at AppArmor's daemon configuration (usually at /etc/apparmor.d/) if you change daemon configuration and run into errors such as the one above.
Trigger native mouse events with Javascript
The attached Coffeescript helper will let you create mouse events:
$element = $('div')
Trigger.mouseover($element)
Trigger.mouseenter($element)
Trigger.mousedown($element)
Trigger.mouseup($element)
Trigger.mouseout($element)
Trigger.mouseleave($element)
Trigger.click($element)
The dispatched events are real DOM events, which will trigger both native and jQuery handlers.
jQuery's .trigger is simpler, but will only trigger event handlers that were bound by jQuery's .on.
Real user actions t…
Trigger a link's click action with Javascript
TLDR
Use the click method from the raw DOM element (not the jQuery object):
$link = $('a:first');
$link[0].click()
Mind the [0].
Long story
Triggering a link's click action seems easy on first sight:
$link = $('a:first');
$link.click()
Unfortunately that only triggers click event handlers that were registered through jQuery. It will not make a link navigate to its href.
To make a link navigate to its href you need to say:
$link = $('a:first');
location.href = $link....
Pitfall: ActiveRecord callbacks: Method call with multiple conditions
In the following example the method update_offices_people_count won't be called when office_id changes, because it gets overwritten by the second line:
after_save :update_offices_people_count, :if => :office_id_changed? # is overwritten …
after_save :update_offices_people_count, :if => :trashed_changed? # … by this line
Instead write:
after_save :update_offices_people_count, :if => :office_people_count_needs_update?
private
def office_people_count_needs_update?
office_id_changed? || trashed_changed?
end
Or, move t…