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# frozen_string_literal: true
module Gitlab
module BackgroundMigration
# CopyColumn is a simple (reusable) background migration that can be used to
# update the value of a column based on the value of another column in the
# same table.
#
# For this background migration to work the table that is migrated _has_ to
# have an `id` column as the primary key.
class CopyColumn
# table - The name of the table that contains the columns.
# copy_from - The column containing the data to copy.
# copy_to - The column to copy the data to.
# start_id - The start ID of the range of rows to update.
# end_id - The end ID of the range of rows to update.
def perform(table, copy_from, copy_to, start_id, end_id)
return unless connection.column_exists?(table, copy_to)
quoted_table = connection.quote_table_name(table)
quoted_copy_from = connection.quote_column_name(copy_from)
quoted_copy_to = connection.quote_column_name(copy_to)
# We're using raw SQL here since this job may be frequently executed. As
# a result dynamically defining models would lead to many unnecessary
# schema information queries.
connection.execute <<-SQL.strip_heredoc
UPDATE #{quoted_table}
SET #{quoted_copy_to} = #{quoted_copy_from}
WHERE id BETWEEN #{start_id} AND #{end_id}
AND #{quoted_copy_from} IS NOT NULL
AND #{quoted_copy_to} IS NULL
SQL
end
def connection
ActiveRecord::Base.connection
end
end
end
end
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