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class ActiveRecord::MigrationContext

Migration Context

MigrationContext sets the context in which a migration is run.

A migration context requires the path to the migrations is set in the migrations_paths parameter. Optionally a schema_migration class can be provided. Multiple database applications will instantiate a SchemaMigration object per database. From the Rake tasks, Rails will handle this for you.


[R] internal_metadata
[R] migrations_paths
[R] schema_migration

Public class methods

Source code GitHub
# File activerecord/lib/active_record/migration.rb, line 1217
def initialize(migrations_paths, schema_migration = nil, internal_metadata = nil)
  @migrations_paths = migrations_paths
  @schema_migration = schema_migration ||
  @internal_metadata = internal_metadata ||

Public instance methods

Runs the migrations in the migrations_path.

If target_version is nil, migrate will run up.

If the current_version and target_version are both 0 then an empty array will be returned and no migrations will be run.

If the current_version in the schema is greater than the target_version, then down will be run.

If none of the conditions are met, up will be run with the target_version.

Source code GitHub
# File activerecord/lib/active_record/migration.rb, line 1236
def migrate(target_version = nil, &block)
  when target_version.nil?
    up(target_version, &block)
  when current_version == 0 && target_version == 0
  when current_version > target_version
    down(target_version, &block)
    up(target_version, &block)

Definition files