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

Migration

=========

One of the main concept in `CubicWeb` is to create incremental applications

and for this purpose multiple actions are provided to facilitate the improvement

of an application and in particular changes 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 needs to be located in the directory `migration` of your

application and nammed accordingly:

::

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

in which : 

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

* *mode* (between the last "_" and the extension ".py") indicates which part

  of the application (RQL server, web server) the script applies to in case

  of distributed installation. 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 to migrate to a particular model version, you always have to first migrate

to a particular `CubicWeb` version. This file can contains 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 <= erudi <= 2.28 at least

  0.15.0: 2.28.0

Base context

------------

The following identifiers are pre-defined in the migration scripts:

* `config`, instance configuration

* `interactive_mode`, boolean indicating that the script is executed in

  an intercative mode or not 

* `appltemplversion`, application model version of the instance

* `applerudiversion`, cubicweb instance version

* `templversion`, installed application model version

* `erudiversion`, installed cubicweb version

* `confirm(question)`, function interrogating the user and returning true

  if the user answers yes, false otherwise (always returns true when in a

  non-interactive mode)

* `_`, function fonction 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 erudi)

* `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 the `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)`, rename 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 nammed 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 the `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 attributes and relations values are specified using the nammed and

  positionned parameters.

Workflow creation

-----------------

The following functions for workflow creation are available in the `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 the

scripts:

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

* `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 the `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)`