Rails ActiveRecord: create_with, where for new records

More 'things I forgot' - using create_with and where in making new records. We can make use of the resulting association to create new records that match our previous parameters.

Photo by Mark Fletcher-Brown on Unsplash

Using `where` for record creation

We all know that you can use `where` to search for a record:

> purchases = Purchase.where(item_name: "Aerodynamic Copper Watch")
  Purchase Load (1.0ms)  SELECT "purchases".* FROM "purchases" WHERE "purchases"."item_name" = ?  [["item_name", "Aerodynamic Copper Watch"]]
=> 
[#<Purchase:0x000000011348e270

But did you know that you can also use the resulting association to create a new record/object with the searched-for values filled in!

Looks something like this:

> purchases = Purchase.where(item_name: "Awesome Socket Wrench")
  Purchase Load (0.2ms)  SELECT "purchases".* FROM "purchases" WHERE "purchases"."item_name" = ?  [["item_name", "Awesome Socket Wrench"]]
=> []
irb(main):019:0> purchases.new
=> 
#<Purchase:0x0000000113314318
 id: nil,
 item_name: "Awesome Socket Wrench",
 quantity: nil,
 purchase_amount: nil,
 purchased_at: nil,
 status: nil,
 customer_id: nil,
 created_at: nil,
 updated_at: nil,
 description: nil>

That `[]` that returns from the `where` call may look like an empty array, but it is actually an empty Association.

> purchases = Purchase.where(item_name: "Awesome Socket Wrench")
  Purchase Load (0.9ms)  SELECT "purchases".* FROM "purchases" WHERE "purchases"."item_name" = ?  [["item_name", "Awesome Socket Wrench"]]
=> []
irb(main):021:0> purchases.class.name
=> "ActiveRecord::Relation"

That’s why we can do `new` and it will create us a record!

Adding more attributes with `create_with`

When you have that association, you can also create more records - with new or different attributes - by using `create_with`

irb(main):025:0> purchases = Purchase.where(item_name: "Awesome Socket Wrench")
  Purchase Load (1.8ms)  SELECT "purchases".* FROM "purchases" WHERE "purchases"."item_name" = ?  [["item_name", "Awesome Socket Wrench"]]
=> []
irb(main):026:0> purchases.create_with(quantity: 1).new
=> 
#<Purchase:0x0000000112ac0f40
 id: nil,
 item_name: "Awesome Socket Wrench",
 quantity: 1,
 purchase_amount: nil,
 purchased_at: nil,
 status: nil,
 customer_id: nil,
 created_at: nil,
 updated_at: nil,
 description: nil>

Now, you know I like to focus on practical, real-world uses for language features. I have to admit that right now I can’t think why you would use this over the other options available, but if you can, drop me a note and I can include it in a future posting!

Don’t forget to check out my videos over on my YouTube channel. I do (often lengthy!) tutorials on Real World Rails applications.