When you have string contents (e.g. a generated binary stream, or data from a remote source) that you want to store as a file using Carrierwave, here is a simple solution.

While you could write your string to a file and pass that file to Carrierwave, why even bother? You already have your string (or stream).
However, a plain StringIO object will not work for Carrierwave's ActiveRecord integration:

>> Attachment.create!(file: StringIO.new(contents))
TypeError: no implicit conversion of nil into String

This is because Carrierwav...

SELECT pg_size_pretty(pg_database_size('some-database'));

Example

SELECT pg_size_pretty(pg_database_size('cards_p'));
----------------
 13 GB
(1 row)

SELECT pg_database_size('cards_p');
 pg_database_size 
------------------
      13524832927
(1 row)

Related

• PostgreSQL: Show size of all databases
• PostgreSQL: How to show table sizes

Web applications can be used by multiple users at the same time. A typical application server like Passenger has multiple worker processes for a single app. In a distributed deployment setup like we use at makandra you will even have multiple application servers, each with their own worker pool.

This means that your code needs to deal with concurrent data access. The two main tools we use to cope with concurrency are database transactions and distributed locks. These two are not interchangeable. You ca...

Ruby includes many standard gems that are bundled into the Ruby installation. Here is an example for the gem strscan that will be displayed as default:

gem list strscan     

*** LOCAL GEMS ***

strscan (default: 3.0.1)

It is still possible to have newer version of a gem installed beside the default version:

gem install strscan  
Fetching strscan-3.0.3.gem
Building native extensions. This could take a while...
Successfully installed strscan-3.0.3
1 gem installed

gem list strscan   

*** LOC...

In case you have trouble with the zeitwerk autoloader, you can check out the documentation Autoloading and Reloading Constants and Classic to Zeitwerk HOWTO for some debugging hints.

For myself it was useful to print the registered constants and the file references during the boot. Therefore you need to add Rails.autoloaders.log! at the end of your config/application.rb file. You could also run `bin...

With ActiveType 1.2 you can modify associations (has_many etc.) after they have been defined.

One common use case for this is to change an association inside a form model, like this:

class Credential < ActiveRecord::Base
end

class User < ActiveRecord::Base
  has_many :credentials
end

class SignUpCredential < ActiveType::Record[Credential]
end

class SignUp < ActiveType::Record[User]
  change_association :credentials, class_name: 'SignUpCredential'
end

Now, if you load `credentials...

Some pseudo-elements need to be addressed with vendor prefixes. E.g. ::selection is not supported by Firefox, you need to use ::-moz-selection instead.

What you cannot do is to define a single CSS rule to address both the standard and vendor-prefixed form:

::selection, ::-moz-selection {
  background-color: red;
}

This rule will be ignored by all browsers. The reason is that if a browser doe...

When you want to group rails models of a logical context, namespaces are your friend. However, if you have a lot of classes in the same namespace it might be tedious to specify the table name for each class seperately:

class Accounting::Invoice < ApplicationRecord
  self.table_name = 'accounting_invoices'
  ...
end

class Accounting::Payment < ApplicationRecord
  self.table_name = 'accounting_payments'
  ...
end

A replacement for the self.table_name-assignment is the table_name_prefix in the module definition:

modu...

Code quality can be measured in four levels:

0. (Working code)
1. Reliable code (minimum)
2. Readable code (ok for short-lived code)
3. Changeable code (standard level)

The code quality of a project directly impacts its maintainability.

Generally you should aim for level 3. If the code will stay for less than a few months, it may stay at level 2. Never go below level 1.

0. Working code

You have implemented that feature and it works. Congrats! You have reached level zero, which means three levels of code quality lie ahead.

First, m...

tl;dr

Since Rails 6.1+ you can use .compact_blank or .compact_blank! to remove blank values from collections (e.g. arrays).

Remove nil values from an array

['foo', nil].compact
# => ['foo']

# You can use the splat operator to ignore nil values when constructing an array
['foo', *nil]
# => ['foo']

Remove blank values from collections

Array

array = [1, "", nil, 2, " ", [], {}, false, true]

# Any Rails version
array.reject(&:blank?)
# => [1, 2, true]

# Since Rails 6.1+
array.compact_blank
# ...

CSS support in major e-mail clients is horrible.

This will give you an overview what you will not be able to use across all clients.

See also

• Designing HTML emails

When paginating records, we usually need to know the number of total records in order to render pagination links. Popular pagination libraries like will_paginate or Kaminari do this for us by simply issuing an extra query, like this:

SELECT post.* FROM posts LIMIT 20 OFFSET 100;

SELECT COUNT(*) FROM posts;   

This is fine most of the time. But rarely, you might have very complicated WHERE conditions or a subquery that takes time to run. In thes...

You can use the code below to check whether the browser can make connections to the current site:

await isOnline() // resolves to true or false

Limitations of navigator.onLine

While you can use the built-in function navigator.onLine (sic), it is only a hint for whether the device can access the Internet.

When navigator.onLine === false you know for certain that the user device has no connection to the Internet. This mea...

Ruby has two different ways to match the start and the end of a text:

• ^ (Start of line) and $ (End of line)
• \A (Start of string) and \z (End of string)

Most often you want to use \A and \z.

Here is a short example in which we want to validate the content type of a file attachment. Normally we would not expect content_type_1 to be a valid content type with the used regular expression image\/(jpeg|png). But as ^ and $ will match lines, it matches both content_type_1 and content_type_2. Using \A and \z will wo...

This note shows how to merge an ugly feature branch with multiple dirty WIP commits back into the master as one pretty commit.

Squashing commits with git rebase

What we are describing here will destroy commit history and can go wrong. For this reason, do the squashing on a separate branch:

git checkout -b squashed_feature

This way, if you screw up, you can go back to your original branch, make another branch for squashing and try again.

Tip

If you didn't make a backup branch and something ...

Somewhat regularly, you will need to filter a list down to some items and then map them to another value.

You can of course chain map and compact, or select/filter and map, but Ruby 2.7 introduced a method for this exact purpose: filter_map.

So instead of

>> [1, 2, 3, 4, 5, 6].map { |i| i * 2 if i.even? }.compact
=> [4, 8, 12]

or

>> [1, 2, 3, 4, 5, 6].select(&:even?).map { |i| i * 2 }
=> [4, 8, 12]

you can just do

>> [1,...

I recently wanted to add a model for address information but also wanted to add a unique index to those fields that is case-insensitive.
The model looked like this:

create_table :shop_locations do |t|
  t.string :street
  t.string :house_number
  t.string :zip_code
  t.string :city
  t.belongs_to :shop
end

But how to solve the uniqueness problem?

Another day, another undocumented Rails feature!

This time, it’s that ActiveRecord::Base.connection.add_index supports an undocumented option to pass a string argument as the v...