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class StatusIdsToTimestampIds < ActiveRecord::Migration[5.1]
def up
# Prepare the function we will use to generate IDs.
Mastodon::Snowflake.define_timestamp_id
# Set up the statuses.id column to use our timestamp-based IDs.
ActiveRecord::Base.connection.execute(<<~SQL)
ALTER TABLE statuses
ALTER COLUMN id
SET DEFAULT timestamp_id('statuses')
SQL
# Make sure we have a sequence to use.
Mastodon::Snowflake.ensure_id_sequences_exist
end
def down
# Revert the column to the old method of just using the sequence
# value for new IDs. Set the current ID sequence to the maximum
# existing ID, such that the next sequence will be one higher.
# We lock the table during this so that the ID won't get clobbered,
# but ID is indexed, so this should be a fast operation.
ActiveRecord::Base.connection.execute(<<~SQL)
LOCK statuses;
SELECT setval('statuses_id_seq', (SELECT MAX(id) FROM statuses));
ALTER TABLE statuses
ALTER COLUMN id
SET DEFAULT nextval('statuses_id_seq');
SQL
end
end