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+++ b/doc/book/devrepo/devcore/dbapi.rst	Thu Jan 08 22:11:06 2015 +0100
@@ -0,0 +1,133 @@
+.. _dbapi:
+
+Python/RQL API
+~~~~~~~~~~~~~~
+
+The Python API developped to interface with RQL is inspired from the standard db-api,
+with a Connection object having the methods cursor, rollback and commit essentially.
+The most important method is the `execute` method of a cursor.
+
+.. sourcecode:: python
+
+   execute(rqlstring, args=None, build_descr=True)
+
+:rqlstring: the RQL query to execute (unicode)
+:args: if the query contains substitutions, a dictionary containing the values to use
+
+The `Connection` object owns the methods `commit` and `rollback`. You
+*should never need to use them* during the development of the web
+interface based on the *CubicWeb* framework as it determines the end
+of the transaction depending on the query execution success. They are
+however useful in other contexts such as tests or custom controllers.
+
+.. note::
+
+  If a query generates an error related to security (:exc:`Unauthorized`) or to
+  integrity (:exc:`ValidationError`), the transaction can still continue but you
+  won't be able to commit it, a rollback will be necessary to start a new
+  transaction.
+
+  Also, a rollback is automatically done if an error occurs during commit.
+
+.. note::
+
+   A :exc:`ValidationError` has a `entity` attribute. In CubicWeb,
+   this atttribute is set to the entity's eid (not a reference to the
+   entity itself).
+
+Executing RQL queries from a view or a hook
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+When you're within code of the web interface, the db-api like connexion is
+handled by the request object. You should not have to access it directly, but
+use the `execute` method directly available on the request, eg:
+
+.. sourcecode:: python
+
+   rset = self._cw.execute(rqlstring, kwargs)
+
+Similarly, on the server side (eg in hooks), there is no db-api connexion (since
+you're directly inside the data-server), so you'll have to use the execute method
+of the session object.
+
+
+Proper usage of `.execute`
+~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+Let's say you want to get T which is in configuration C, this translates to:
+
+.. sourcecode:: python
+
+   self._cw.execute('Any T WHERE T in_conf C, C eid %s' % entity.eid)
+
+But it must be written in a syntax that will benefit from the use
+of a cache on the RQL server side:
+
+.. sourcecode:: python
+
+   self._cw.execute('Any T WHERE T in_conf C, C eid %(x)s', {'x': entity.eid})
+
+The syntax tree is built once for the "generic" RQL and can be re-used
+with a number of different eids. There rql IN operator is an exception
+to this rule.
+
+.. sourcecode:: python
+
+   self._cw.execute('Any T WHERE T in_conf C, C name IN (%s)'
+                    % ','.join(['foo', 'bar']))
+
+Alternativelly, some of the common data related to an entity can be
+obtained from the `entity.related()` method (which is used under the
+hood by the orm when you use attribute access notation on an entity to
+get a relation. The initial request would then be translated to:
+
+.. sourcecode:: python
+
+   entity.related('in_conf', 'object')
+
+Additionnaly this benefits from the fetch_attrs policy (see
+:ref:`FetchAttrs`) eventually defined on the class element, which says
+which attributes must be also loaded when the entity is loaded through
+the orm.
+
+
+.. _resultset:
+
+The `ResultSet` API
+~~~~~~~~~~~~~~~~~~~
+
+ResultSet instances are a very commonly manipulated object. They have
+a rich API as seen below, but we would like to highlight a bunch of
+methods that are quite useful in day-to-day practice:
+
+* `__str__()` (applied by `print`) gives a very useful overview of both
+  the underlying RQL expression and the data inside; unavoidable for
+  debugging purposes
+
+* `printable_rql()` produces back a well formed RQL expression as a
+  string; it is very useful to build views
+
+* `entities()` returns a generator on all entities of the result set
+
+* `get_entity(row, col)` gets the entity at row, col coordinates; one
+  of the most used result set method
+
+.. autoclass:: cubicweb.rset.ResultSet
+   :members:
+
+
+The `Cursor` and `Connection` API
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+The whole cursor API is developped below.
+
+.. note::
+
+  In practice you'll usually use the `.execute` method on the _cw object of
+  appobjects. Usage of other methods is quite rare.
+
+.. autoclass:: cubicweb.dbapi.Cursor
+   :members:
+
+.. autoclass:: cubicweb.dbapi.Connection
+   :members: