.. -*- coding: utf-8 -*-

.. _migration:

Migration
=========

One of the main concept in `CubicWeb` is to create incremental applications.
For this purpose, multiple actions are provided to facilitate the improvement
of an application, and in particular to handle the changes to be applied
to the data model, without loosing existing data.

The current version of an application model is provided in the file
`__pkginfo__.py` as a tuple of 3 integers.

Migration scripts management
----------------------------

Migration scripts has to be located in the directory `migration` of your
application and named accordingly:

::

  <version n° X.Y.Z>[_<description>]_<mode>.py

in which :

* X.Y.Z is the model version number to which the script enables to migrate.

* *mode* (between the last "_" and the extension ".py") is used for
  distributed installation. It indicates to which part
  of the application (RQL server, web server) the script applies.
  Its value could be :

  * `common`, applies to the RQL server as well as the web server and updates
    files on the hard drive (configuration files migration for example).

  * `web`, applies only to the web server and updates files on the hard drive.

  * `repository`, applies only to the RQL server and updates files on the
    hard drive.

  * `Any`, applies only to the RQL server and updates data in the database
    (schema and data migration for example).

Again in the directory `migration`, the file `depends.map` allows to indicate
that for the migration to a particular model version, you always have to first
migrate to a particular `CubicWeb` version. This file can contain comments (lines
starting by `#`) and a dependancy is listed as follows: ::

  <model version n° X.Y.Z> : <cubicweb version n° X.Y.Z>

For example: ::

  0.12.0: 2.26.0
  0.13.0: 2.27.0
  # 0.14 works with 2.27 <= cubicweb <= 2.28 at least
  0.15.0: 2.28.0

Base context
------------

The following identifiers are pre-defined in migration scripts:

* `config`, instance configuration

* `interactive_mode`, boolean indicating that the script is executed in
  an interactive mode or not

* `appltemplversion`, application model version of the instance

* `templversion`, installed application model version

* `cubicwebversion`, installed cubicweb version

* `confirm(question)`, function asking the user and returning true
  if the user answers yes, false otherwise (always returns true in
  non-interactive mode)

* the function `_`, it is equivalent to `unicode` allowing to flag the strings
  to internationalize in the migration scripts.

In the `repository` scripts, the following identifiers are also defined:

* `checkpoint`, request confirming and executing a "commit" at checking point

* `repo_schema`, instance persisting schema (e.g. instance schema of the
  current migration)

* `newschema`, installed schema on the file system (e.g. schema of
  the updated model and cubicweb)

* `sqlcursor`, SQL cursor for very rare cases where it is really
   necessary or beneficial to go through the sql

* `repo`, repository object


Schema migration
----------------
The following functions for schema migration are available in `repository`
scripts:

* `add_attribute(etype, attrname, attrtype=None, commit=True)`, adds a new
  attribute to an existing entity type. If the attribute type is not specified,
  then it is extracted from the updated schema.

* `drop_attribute(etype, attrname, commit=True)`, removes an attribute from an
  existing entity type.

* `rename_attribute(etype, oldname, newname, commit=True)`, renames an attribute

* `add_entity_type(etype, auto=True, commit=True)`, adds a new entity type.
  If `auto` is True, all the relations using this entity type and having a known
  entity type on the other hand will automatically be added.

* `drop_entity_type(etype, commit=True)`, removes an entity type and all the
  relations using it.

* `rename_entity_type(oldname, newname, commit=True)`, renames an entity type

* `add_relation_type(rtype, addrdef=True, commit=True)`, adds a new relation
  type. If `addrdef` is True, all the relations definitions of this type will
  be added.

* `drop_relation_type(rtype, commit=True)`, removes a relation type and all the
  definitions of this type.

* `rename_relation(oldname, newname, commit=True)`, renames a relation.

* `add_relation_definition(subjtype, rtype, objtype, commit=True)`, adds a new
  relation definition.

* `drop_relation_definition(subjtype, rtype, objtype, commit=True)`, removes
  a relation definition.

* `synchronize_permissions(ertype, commit=True)`, synchronizes permissions on
  an entity type or relation type.

* `synchronize_rschema(rtype, commit=True)`, synchronizes properties and permissions
  on a relation type.

* `synchronize_eschema(etype, commit=True)`, synchronizes properties and persmissions
  on an entity type.

* `synchronize_schema(commit=True)`, synchronizes the persisting schema with the
  updated schema (but without adding or removing new entity types, relations types
  or even relations definitions).

* `change_relation_props(subjtype, rtype, objtype, commit=True, **kwargs)`, changes
  properties of a relation definition by using the named parameters of the properties
  to change.

* `set_widget(etype, rtype, widget, commit=True)`, changes the widget used for the
  relation <rtype> of entity type <etype>.

* `set_size_constraint(etype, rtype, size, commit=True)`, changes the size constraints
  for the relation <rtype> of entity type <etype>.

Data migration
--------------
The following functions for data migration are available in `repository` scripts:

* `rql(rql, kwargs=None, cachekey=None, ask_confirm=True)`, executes an arbitrary RQL
  query, either to interrogate or update. A result set object is returned.

* `add_entity(etype, *args, **kwargs)`, adds a nes entity type of the given
  type. The attribute and relation values are specified using the named and
  positionned parameters.

Workflow creation
-----------------

The following functions for workflow creation are available in `repository`
scripts:

* `add_state(name, stateof, initial=False, commit=False, **kwargs)`, adds a new state
  in the workflow.

* `add_transition(name, transitionof, fromstates, tostate, requiredgroups=(), commit=False, **kwargs)`,
  adds a new transition in the workflow.

You can find more details about workflows in the chapter :ref:`Workflow` .

Configuration migration
-----------------------

The following functions for configuration migration are available in all
scripts:

* `option_renamed(oldname, newname)`, indicates that an option has been renamed

* `option_group_change(option, oldgroup, newgroup)`, indicates that an option does not
  belong anymore to the same group.

* `option_added(oldname, newname)`, indicates that an option has been added.

* `option_removed(oldname, newname)`, indicates that an option has been deleted.


Others migration functions
--------------------------
Those functions are only used for low level operations that could not be
accomplished otherwise or to repair damaged databases during interactive
session. They are available in `repository` scripts:

* `sqlexec(sql, args=None, ask_confirm=True)`, executes an arbitrary SQL query
* `add_entity_type_table(etype, commit=True)`
* `add_relation_type_table(rtype, commit=True)`
* `uninline_relation(rtype, commit=True)`


[FIXME] Add explanation on how to use cubicweb-ctl shell