--- /dev/null
+== Running Migrations ==
+
+Rails provides a set of rake tasks to work with migrations which boils down to running certain sets of migrations. The very first migration related rake task you use will probably be `db:migrate`. In its most basic form it just runs the `up` method for all the migrations that have not yet been run. If there are no such migrations it exits.
+
+If you specify a target version, Active Record will run the required migrations (up or down) until it has reached the specified version. The
+version is the numerical prefix on the migration's filename. For example to migrate to version 20080906120000 run
+
+------------------------------------
+rake db:migrate VERSION=20080906120000
+------------------------------------
+
+If this is greater than the current version (i.e. it is migrating upwards) this will run the `up` method on all migrations up to and including 20080906120000, if migrating downwards this will run the `down` method on all the migrations down to, but not including, 20080906120000.
+
+=== Rolling back ===
+
+A common task is to rollback the last migration, for example if you made a mistake in it and wish to correct it. Rather than tracking down the version number associated with the previous migration you can run
+
+------------------
+rake db:rollback
+------------------
+
+This will run the `down` method from the latest migration. If you need to undo several migrations you can provide a `STEP` parameter:
+
+------------------
+rake db:rollback STEP=3
+------------------
+
+will run the `down` method from the last 3 migrations.
+
+The `db:migrate:redo` task is a shortcut for doing a rollback and then migrating back up again. As with the `db:rollback` task you can use the `STEP` parameter if you need to go more than one version back, for example
+
+------------------
+rake db:migrate:redo STEP=3
+------------------
+
+Neither of these Rake tasks do anything you could not do with `db:migrate`, they are simply more convenient since you do not need to explicitly specify the version to migrate to.
+
+Lastly, the `db:reset` task will drop the database, recreate it and load the current schema into it.
+
+NOTE: This is not the same as running all the migrations - see the section on <<schema,schema.rb>>.
+
+=== Being Specific ===
+
+If you need to run a specific migration up or down the `db:migrate:up` and `db:migrate:down` tasks will do that. Just specify the appropriate version and the corresponding migration will have its `up` or `down` method invoked, for example
+
+------------------
+rake db:migrate:up VERSION=20080906120000
+------------------
+
+will run the `up` method from the 20080906120000 migration. These tasks check whether the migration has already run, so for example `db:migrate:up VERSION=20080906120000` will do nothing if Active Record believes that 20080906120000 has already been run.
+
+
+=== Being talkative ===
+
+By default migrations tell you exactly what they're doing and how long it took.
+A migration creating a table and adding an index might produce output like this
+-------------------------
+== 20080906170109 CreateProducts: migrating ===================================
+-- create_table(:products)
+ -> 0.0021s
+-- add_index(:products, :name)
+ -> 0.0026s
+== 20080906170109 CreateProducts: migrated (0.0059s) ==========================
+-------------------------
+Several methods are provided that allow you to control all this:
+
+* `suppress_messages` suppresses any output generated by its block
+* `say` outputs text (the second argument controls whether it is indented or not)
+* `say_with_time` outputs text along with how long it took to run its block. If the block returns an integer it assumes it is the number of rows affected.
+
+For example, this migration
+
+[source, ruby]
+----------------------
+class CreateProducts < ActiveRecord::Migration
+ def self.up
+ suppress_messages do
+ create_table :products do |t|
+ t.string :name
+ t.text :description
+ t.timestamps
+ end
+ end
+ say "Created a table"
+ suppress_messages {add_index :products, :name}
+ say "and an index!", true
+ say_with_time 'Waiting for a while' do
+ sleep 10
+ 250
+ end
+ end
+
+ def self.down
+ drop_table :products
+ end
+end
+----------------------
+
+generates the following output
+----------------------
+== 20080906170109 CreateProducts: migrating ===================================
+-- Created a table
+ -> and an index!
+-- Waiting for a while
+ -> 10.0001s
+ -> 250 rows
+== 20080906170109 CreateProducts: migrated (10.0097s) =========================
+----------------------
+
+If you just want Active Record to shut up then running `rake db:migrate VERBOSE=false` will suppress any output.
+
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