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+.. -*- coding: utf-8 -*-
+
+.. _migration:
+
+Migration
+=========
+
+One of the main design goals of *CubicWeb* was to support iterative and agile
+development. For this purpose, multiple actions are provided to facilitate the
+improvement of an instance, and in particular to handle the changes to be
+applied to the data model, without loosing existing data.
+
+The current version of a cube (and of cubicweb itself) 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
+cube 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 with `#`) and a dependency 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
+
+* `versions_map`, dictionary of migrated versions  (key are cubes
+  names, including 'cubicweb', values are (from version, to version)
+
+* `confirm(question)`, function asking the user and returning true
+  if the user answers yes, false otherwise (always returns true in
+  non-interactive mode)
+
+* `_()` 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:
+
+* `commit(ask_confirm=True)`, request confirming and executing a "commit"
+
+* `schema`, instance schema (readen from the database)
+
+* `fsschema`, installed schema on the file system (e.g. schema of
+  the updated model and cubicweb)
+
+* `repo`, repository object
+
+* `session`, repository session object
+
+
+New cube dependencies
+---------------------
+
+If your code depends on some new cubes, you have to add them in a migration
+script by using:
+
+* `add_cube(cube, update_database=True)`, add a cube.
+* `add_cubes(cubes, update_database=True)`, add a list of cubes.
+
+The `update_database` parameter is telling if the database schema
+should be updated or if only the relevant persistent property should be
+inserted (for the case where a new cube has been extracted from an
+existing one, so the new cube schema is actually already in there).
+
+If some of the added cubes are already used by an instance, they'll simply be
+silently skipped.
+
+
+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_type(oldname, newname, commit=True)`, renames a relation type.
+
+* `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.
+
+* `sync_schema_props_perms(ertype=None, syncperms=True, syncprops=True, syncrdefs=True, commit=True)`,
+  synchronizes properties and/or permissions on:
+  - the whole schema if ertype is None
+  - an entity or relation type schema if ertype is a string
+  - a relation definition  if ertype is a 3-uple (subject, relation, object)
+
+* `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 new entity of the given type.
+  The attribute and relation values are specified as named positional
+  arguments.
+
+Workflow creation
+-----------------
+
+The following functions for workflow creation are available in `repository`
+scripts:
+
+* `add_workflow(label, workflowof, initial=False, commit=False, **kwargs)`, adds a new workflow
+  for a given type(s)
+
+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.
+
+The `config` variable is an object which can be used to access the
+configuration values, for reading and updating, with a dictionary-like
+syntax. 
+
+Example 1: migration script changing the variable 'sender-addr' in
+all-in-one.conf. The script also checks that in that the instance is
+configured with a known value for that variable, and only updates the
+value in that case.
+
+.. sourcecode:: python
+
+ wrong_addr = 'cubicweb@loiglab.fr' # known wrong address
+ fixed_addr = 'cubicweb@logilab.fr'
+ configured_addr = config.get('sender-addr')
+ # check that the address has not been hand fixed by a sysadmin
+ if configured_addr == wrong_addr: 
+     config['sender-addr'] = fixed-addr
+     config.save()
+
+Example 2: checking the value of the database backend driver, which
+can be useful in case you need to issue backend-dependent raw SQL
+queries in a migration script.
+
+.. sourcecode:: python
+
+ dbdriver  = config.sources()['system']['db-driver']
+ if dbdriver == "sqlserver2005":
+     # this is now correctly handled by CW :-)
+     sql('ALTER TABLE cw_Xxxx ALTER COLUMN cw_name varchar(64) NOT NULL;')
+     commit()
+ else: # postgresql
+     sync_schema_props_perms(ertype=('Xxxx', 'name', 'String'),
+     syncperms=False)
+
+
+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:
+
+* `sql(sql, args=None, ask_confirm=True)`, executes an arbitrary SQL query on the system source
+* `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