How do I check the Database type in a Rails Migration?

Question

I have the following migration and I want to be able to check if the current database related to the environment is a mysql database. If it's mysql then I want to execute the SQL that is specific to the database.

How do I go about this?

class AddUsersFb < ActiveRecord::Migration

  def self.up
    add_column :users, :fb_user_id, :integer
    add_column :users, :email_hash, :string
    #if mysql
    #execute("alter table users modify fb_user_id bigint")
  end

  def self.down
    remove_column :users, :fb_user_id
    remove_column :users, :email_hash
  end

end

score 60 · Answer 1 · answered Mar 29 '10 at 08:59

60

Even more shorter call

ActiveRecord::Base.connection.adapter_name == 'MySQL'

answered Mar 29 '10 at 08:59

stasl

953
7
6

7

I'm using the mysql2 gem, and I suspect some others might at this point, so I use the following: `ActiveRecord::Base.connection.adapter_name.downcase.starts_with? 'mysql'` – bensnider Jan 11 '13 at 21:03
6

`ActiveRecord::Base.connection.adapter_name == "Mysql2"` worked for me with Rails 4. – Jason Aug 05 '13 at 21:12

score 46 · Accepted Answer · edited Apr 16 '15 at 16:38

ActiveRecord::Base.connection will provide you with everything you ever wanted to know about the database connection established by boot.rb and environment.rb

ActiveRecord::Base.connection returns a lot of information. So you've got to know exactly what you're looking for.

As Marcel points out:

ActiveRecord::Base.connection.instance_of? 
  ActiveRecord::ConnectionAdapters::MysqlAdapter

is probably the best method of determining if your database MySQL.

Despite relying on internal information that could change between ActiveRecord release, I prefer doing it this way:

ActiveRecord::Base.connection.instance_values["config"][:adapter] == "mysql"

`ActiveRecord::Base.connection.instance_of? ActiveRecord::ConnectionAdapters::MysqlAdapter` should solve it. — Marcel Jackwerth, Oct 27 '09 at 03:49

KARASZI István · Answer 3 · 2020-05-27T09:24:05.507

29

There is an adapter_name in AbstractAdapter and that is there since Rails2.

So it's easier to use in the migration like this:

adapter_type = connection.adapter_name.downcase.to_sym
case adapter_type
when :mysql, :mysql2
  # do the MySQL part
when :sqlite
  # do the SQLite3 part
when :postgresql
  # etc.
else
  raise NotImplementedError, "Unknown adapter type '#{adapter_type}'"
end

edited May 27 '20 at 09:24

answered Apr 14 '11 at 15:51

KARASZI István

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3

This won't work with the mysql2 gem—you can just edit the line to be ```when :mysql, :mysql2```. – mrm Jun 15 '13 at 17:50
Your answer is more complete and clean. Thanks. – Cassio Cabral Mar 07 '14 at 01:49
For postgres: ` def is_postgres? name = ActiveRecord::Base.connection.adapter_name.downcase name =~ /postgres/ end ` – Blaskovicz Jan 26 '17 at 17:13

score 8 · Answer 4 · answered Jan 21 '11 at 19:21

In Rails 3, (maybe earlier, but I'm using Rails 3 currently) using ActiveRecord::ConnectionAdapters::MysqlAdapter is a poor way to go about it, as it's only initialized if the database adapter in use is MySQL. Even if you have the MySQL gem installed, if it's not your connection type, that call wil fail:

Loading development environment (Rails 3.0.3)
>> ActiveRecord::Base.connection.instance_of? ActiveRecord::ConnectionAdapters::MysqlAdapter
NameError: uninitialized constant ActiveRecord::ConnectionAdapters::MysqlAdapter
from (irb):1

So, I'd recommend stasl's answer and use the adapter_name property of the connection.

score -4 · Answer 5 · answered Oct 27 '09 at 03:37

-4

This might help:

execute 'alter table users modify fb_user_id bigint WHERE USER() = "mysqluser";'

answered Oct 27 '09 at 03:37

CodeJoust

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It won't work when the user is different and won't work any databases where `USER()` function is not defined, for e.g. SQLite. – KARASZI István Apr 20 '11 at 10:55

How do I check the Database type in a Rails Migration?

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