Active Record loves blocks

I’d like to start with a question: Have you ever seen code like this?

class User 

I have. But what few developers know is that many methods in Active Record already accept a block, so you don't need to invoke tap in the first place. And that's all because Active Record loves blocks! Let's go through some examples.

Using blocks with Active Record

When creating an Active Record object, either by using new or create/create!, you can give a block straight to the method call instead of relying on tap: do |user|     = "John Doe"
  user.username = "john.doe"
  user.password = "john123"

User.create do |user|     = "John Doe"
  user.username = "john.doe"
  user.password = "john123"

And you can mix and match with hash initialization: "John Doe") do |user|
  user.username = "john.doe"
  user.password = "john123"

All these methods, when receiving a block, yield the current object to the block so that you can do whatever you want with it. It's basically the same effect as using tap. And it all happens after the attributes hash have been assigned and other internal Active Record code has been run during the object initialization, except by the after_initialize callbacks.

That's neat. That means we can stop using tap in a few places now. But wait, there's more.

Active Record associations also love blocks

We talked about using blocks when building an Active Record object using new or create, but associations like belongs_to or has_many also work with that, when calling build or create on them:

class User 

That's even better. That means we can stop using tap in a few more places.

Wrapping up: Active Record <3 blocks

It is possible to avoid extra work, sometimes simple stuff such as using tap with methods like new and create, other times more complicated ones, by getting to know what the framework can give us for free.

There are other places inside Active Record that accept blocks, for instance first_or_initialize and friends will execute the given block when the record is not found, to initialize the new one.

In short, next time you need a block when creating records using Active Record, take a minute to see if you can avoid using tap by using an already existing feature. Remember: Active Record <3 blocks. And don't do that with blocks only, the main idea here is that you can learn more about the framework, and let it do more work for you.

How about you, do you have any small trick in Ruby or Rails that makes your work easier? Take a minute to share it with others in the comments. 🙂

8 responses to “Active Record loves blocks”

  1. Shemerey says:

    yet another good example about scoping 
    Developer.where(“salary = 9000”).scoping do
          Developer.where(“name = ‘Jamis'”).first

  2. Fabiano Vilela says:


  3. Nice, thanks for sharing.

  4. Here’s how I tested the above:

  5. Cool, didn’t know that. Thanks Charles!

  6. googya says:

    thanks for sharing! I used the tap method all the time, now can write less code! 

  7. jrochkind says:

    would one find it mentioned in the docs anywhere that these methods take blocks? How’d you figure it out?  If I remember in the future “oh yeah, some AR methods take blocks but I forget which ones and how”, is there a way to look this up in the docs, or am I reduced to googling for your blog post?

  8. Some of these methods are documented inside the Active Record API, like here:, but I’m afraid not all possibilites are covered – which leaves us with some source diving to figure out all of them. Of course, since you know that the basic ones are documented, similar methods should just work the same.

    Anyway, a pull request (or committing to lifo/docrails) improving the docs where necessary would be more than welcome :). Thanks!