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migrations guide: fix and edits [ci skip]

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Xavier Noria 2013-08-05 16:36:50 +02:00
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16
guides/source/migrations.md
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@ -829,8 +829,7 @@ which contains a `Product` model:
Bob goes on vacation.
Alice creates a migration for the `products` table which adds a new column and
initializes it. She also adds a validation to the `Product` model for the new
column.
initializes it:
```ruby
# db/migrate/20100513121110_add_flag_to_product.rb
@ -845,6 +844,8 @@ class AddFlagToProduct < ActiveRecord::Migration
end
```
She also adds a validation to the `Product` model for the new column:
```ruby
# app/models/product.rb
@ -853,9 +854,8 @@ class Product < ActiveRecord::Base
end
```
Alice adds a second migration which adds and initializes another column to the
`products` table and also adds a validation to the `Product` model for the new
column.
Alice adds a second migration which adds another column to the `products`
table and initializes it:
```ruby
# db/migrate/20100515121110_add_fuzz_to_product.rb
@ -870,6 +870,8 @@ class AddFuzzToProduct < ActiveRecord::Migration
end
```
She also adds a validation to the `Product` model for the new column:
```ruby
# app/models/product.rb
@ -903,7 +905,7 @@ A fix for this is to create a local model within the migration. This keeps
Rails from running the validations, so that the migrations run to completion.
When using a local model, it's a good idea to call
`Product.reset_column_information` to refresh the `ActiveRecord` cache for the
`Product.reset_column_information` to refresh the Active Record cache for the
`Product` model prior to updating data in the database.
If Alice had done this instead, there would have been no problem:
@ -956,7 +958,7 @@ other product attributes.
These migrations run just fine, but when Bob comes back from his vacation
and calls `rake db:migrate` to run all the outstanding migrations, he gets a
subtle bug: The descriptions have defaults, and the `fuzz` column is present,
but `fuzz` is nil on all products.
but `fuzz` is `nil` on all products.
The solution is again to use `Product.reset_column_information` before
referencing the Product model in a migration, ensuring the Active Record's