How can execute multiple statements in one query with Rails?

Question

I am using Ruby on Rails with ActiveRecord and PostgreSQL.

How can i execute multiple sql queries?

I need it for running a custom migration script, eg:

Foo.connection.execute <<-SQL.split(';').map(&:strip).join
 delete from metadata where record_type = 'Foo';
 TRUNCATE table1 RESTART IDENTITY;
 TRUNCATE table2 RESTART IDENTITY;
 delete from schema_migrations where version > '20120806120823';
SQL

I am not accepting data from a user, so I'm not worried about sql-injection.

Something like CLIENT_MULTI_STATEMENTS in MySQL maybe ?

From the MySQL/PHP docs:

CLIENT_MULTI_STATEMENTS: Tell the server that the client may send multiple statements in a single string (separated by “;”). If this flag is not set, multiple-statement execution is disabled. See the note following this table for more information about this flag.

Solution 1

It should work out of the box with PostgreSQL, checked with pg gem and rails 3.2:

class Multitest < ActiveRecord::Migration
  def up
    execute <<-SQL
      create table x(id serial primary key);
      create table y(id serial primary key, i integer);
    SQL
  end

  def down
  end
end

On a side note, manipulating schema_migrations directly looks strange.

Solution 2

For mysql

queries = File.read("/where/is/myqueries.sql")
# or
queries = <<-SQL
 TRUNCATE table1 RESTART IDENTITY;
 TRUNCATE table2 RESTART IDENTITY;
 delete from schema_migrations where version > '20120806120823';
SQL

queries.split(';').map(&:strip).each do |query| 
  execute(query)
end

You may want see this question too: Invoking a large set of SQL from a Rails 4 application

Solution 3

Yes, you need CLIENT_MULTI_STATEMENTS:

In database.yml:

development:
  adapter: mysql2
  database: project_development
  flags:
    - MULTI_STATEMENTS

Then in your code:

connection.execute(multistatement_query)
# Hack for mysql2 adapter to be able query again after executing multistatement_query
connection.raw_connection.store_result while connection.raw_connection.next_result

See https://stackoverflow.com/a/11246837/338859 for details

Comments

[deepak]

thanks, i will check the code for migrations. But how does migration's execute work but ActiveRecord's does not? How to run multiple queries from ActiveRecord ?

[Noah Gibbs]

Doesn't work for MySQL, though. ActiveRecord's execute succeeds w/ multiple on Postgres, fails on MySQL.