Adding default values to rails 4 migrations and updating existing records

Question

Recently I realized that none of my database columns have default values. If an object is instantiated and then saved, it might have nil values for any fields that aren't filled out.

I can make it so that I explicitly initialize these values, but then I've got some places where two controllers are creating the same object, but I didn't think of moving that code into a separate module.

I can also choose to update my migrations to specify default values, which seems cleaner.

I've decided to go with migrations. It is not a good idea to edit old migrations, so I'm creating a new migration and specifying that I want to change certain columns.

Looking at how I should change columns, I have determined that I will use this

def change
  change_column :products, :size, :default => 0
end

Will this modify existing records that currently have nil set for those records?

Anezio Campos · Accepted Answer · 2014-08-04 23:47:59Z

2

No, it will not update your old records.

You should NEVER change old migrations, it is a relief you noticed that.

I suggest you to create a rake task that will update all the fields OR you can do it directly on console like the code below.

Product.update_all({ size: 0 }, { size: nil })

answered Aug 4, 2014 at 23:47

Anezio Campos

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3 Comments

Vasseurth Over a year ago

Why is it bad practice to change old migrations? If you do, couldn't you simply db:drop and db:create, if needed?

Anezio Campos Over a year ago

Imagine you have created the migrations and executed on production, or if someone else that is working on the same project with you got your migrations and executed, and after that you change old migrations. It will create some issues.

makhan Over a year ago

Adding it here because I can never find it. If you want to execute a method for every product use find_each: Product.find_each{ |p| p.do_something! }

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