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Rails migrations: String to Text and back again. It's kind of complicated to update a database column that is currently a "string" and convert it into "text." Well, it's not hard to update the column, but it can be dangerous if you need to rollback the migration - Postgresql and other databases don't like adding a limit to the column, and the `r…
class ChangeProductLongDescription < ActiveRecord::Migration
def up
# simple and straightforward
change_column :products, :long_description, :text
end
# but why cant it just be:
# change_column :product, :long_description, :string
# ???
# because effin databases don't like you, that's why.
def down
# create a temporary column to hold the truncated values
# we'll rename this later to the original column name
add_column :products, :temp_description, :string
# use #find_each to load only part of the table into memory
Product.find_each do |product|
temp_description = product.long_description
# test if the new value will fit into the truncated field
if product.long_description.length > 255
temp_description = product.long_description[0,254]
end
# use #update_column because it skips validations AND callbacks
product.update_column(:temp_description, temp_description)
end
# delete the old column since we have all the data safe in the
# temp_description
remove_column :products, :long_description
# rename the temp_column to our original column name
rename_column :products, :temp_description, :long_description
end
end
@jogam5
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jogam5 commented Dec 19, 2014

It worked perfectly when doing a rollback, thanks for sharing!

@rossfeller
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Thanks for sharing!

I ran into one issue where long_description can be nil in my database, so I needed to change L22 to

if product.long_description && product.long_description.length > 255

@vivipoit
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Very helpful! 👍

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