discourse/lib/table_migration_helper.rb

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class TableMigrationHelper
def self.read_only_table(table_name)
ActiveRecord::Base.exec_sql <<-SQL
CREATE OR REPLACE FUNCTION raise_read_only() RETURNS trigger AS $rro$
BEGIN
RAISE EXCEPTION 'Table is read only';
RETURN null;
END
$rro$ LANGUAGE plpgsql;
SQL
ActiveRecord::Base.exec_sql <<-SQL
CREATE TRIGGER #{table_name}_read_only
BEFORE INSERT OR UPDATE OR DELETE OR TRUNCATE
ON #{table_name}
FOR EACH STATEMENT
EXECUTE PROCEDURE raise_read_only();
SQL
end
def self.delayed_drop(old_name:, new_name:, after_migration:, delay: nil, on_drop: nil)
delay ||= Rails.env.production? ? 300 : 0
sql = <<SQL
SELECT 1
FROM INFORMATION_SCHEMA.TABLES
WHERE table_schema = 'public' AND
table_name = :old_name AND
EXISTS (
SELECT 1
FROM schema_migration_details
WHERE name = :after_migration AND
created_at <= (current_timestamp at time zone 'UTC' - interval :delay)
)
AND EXISTS (
SELECT 1
FROM INFORMATION_SCHEMA.TABLES
WHERE table_schema = 'public' AND
table_name = :new_name
)
LIMIT 1
SQL
if ActiveRecord::Base.exec_sql(sql, old_name: old_name,
new_name: new_name,
delay: "#{delay.to_i || 0} seconds",
after_migration: after_migration).to_a.length > 0
on_drop&.call
ActiveRecord::Base.exec_sql("DROP TABLE #{old_name}")
end
end
end