[MOV] howto/rdtraining: move "Getting started" to the tutorials dir

This commit also replaces references to the "Building a module"
tutorial by references to the "Getting started" tutorial.

task-2991663

X-original-commit: 4f4e346953
Part-of: odoo/documentation#3659

content/developer/tutorials/getting_started/11_constraints.rst

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+.. _tutorials/getting_started/11_constraints:
+
+=======================
+Chapter 11: Constraints
+=======================
+
+The :ref:`previous chapter <tutorials/getting_started/10_actions>` introduced the ability to add
+some business logic to our model. We can now link buttons to business code, but how can we prevent
+users from entering incorrect data? For example, in our real estate module nothing prevents
+users from setting a negative expected price.
+
+Odoo provides two ways to set up automatically verified invariants:
+:func:`Python constraints <odoo.api.constrains>` and
+:attr:`SQL constraints <odoo.models.Model._sql_constraints>`.
+
+SQL
+===
+
+**Reference**: the documentation related to this topic can be found in
+:ref:`reference/orm/models` and in the `PostgreSQL's documentation`_.
+
+.. note::
+
+    **Goal**: at the end of this section:
+
+    - Amounts should be (strictly) positive
+
+    .. image:: 11_constraints/sql_01.gif
+        :align: center
+        :alt: Constraints on amounts
+
+    - Property types and tags should have a unique name
+
+    .. image:: 11_constraints/sql_02.gif
+        :align: center
+        :alt: Constraints on names
+
+SQL constraints are defined through the model attribute
+:attr:`~odoo.models.Model._sql_constraints`. This attribute is assigned a list
+of triples containing strings ``(name, sql_definition, message)``, where ``name`` is a
+valid SQL constraint name, ``sql_definition`` is a table_constraint_ expression
+and ``message`` is the error message.
+
+You can find a simple example
+`here <https://github.com/odoo/odoo/blob/24b0b6f07f65b6151d1d06150e376320a44fd20a/addons/analytic/models/analytic_account.py#L20-L23>`__.
+
+.. exercise:: Add SQL constraints.
+
+    Add the following constraints to their corresponding models:
+
+    - A property expected price must be strictly positive
+    - A property selling price must be positive
+    - An offer price must be strictly positive
+    - A property tag name and property type name must be unique
+
+    Tip: search for the ``unique`` keyword in the Odoo codebase for examples of unique names.
+
+Restart the server with the ``-u estate`` option to see the result. Note that you might have data
+that prevents a SQL constraint from being set. An error message similar to the following might pop up:
+
+.. code-block:: text
+
+    ERROR rd-demo odoo.schema: Table 'estate_property_offer': unable to add constraint 'estate_property_offer_check_price' as CHECK(price > 0)
+
+For example, if some offers have a price of zero, then the constraint can't be applied. You can delete
+the problematic data in order to apply the new constraints.
+
+Python
+======
+
+**Reference**: the documentation related to this topic can be found in
+:func:`~odoo.api.constrains`.
+
+.. note::
+
+    **Goal**: at the end of this section, it will not be possible to accept an offer
+    lower than 90% of the expected price.
+
+    .. image:: 11_constraints/python.gif
+        :align: center
+        :alt: Python constraint
+
+SQL constraints are an efficient way of ensuring data consistency. However it may be necessary
+to make more complex checks which require Python code. In this case we need a Python constraint.
+
+A Python constraint is defined as a method decorated with
+:func:`~odoo.api.constrains` and is invoked on a recordset. The decorator
+specifies which fields are involved in the constraint. The constraint is automatically evaluated
+when any of these fields are modified . The method is expected to
+raise an exception if its invariant is not satisfied::
+
+    from odoo.exceptions import ValidationError
+
+    ...
+
+    @api.constrains('date_end')
+    def _check_date_end(self):
+        for record in self:
+            if record.date_end < fields.Date.today():
+                raise ValidationError("The end date cannot be set in the past")
+        # all records passed the test, don't return anything
+
+A simple example can be found
+`here <https://github.com/odoo/odoo/blob/274dd3bf503e1b612179db92e410b336bfaecfb4/addons/stock/models/stock_quant.py#L239-L244>`__.
+
+.. exercise:: Add Python constraints.
+
+    Add a constraint so that the selling price cannot be lower than 90% of the expected price.
+
+    Tip: the selling price is zero until an offer is validated. You will need to fine tune your
+    check to take this into account.
+
+    .. warning::
+
+        Always use the :meth:`~odoo.tools.float_utils.float_compare` and
+        :meth:`~odoo.tools.float_utils.float_is_zero` methods from `odoo.tools.float_utils` when
+        working with floats!
+
+    Ensure the constraint is triggered every time the selling price or the expected price is changed!
+
+SQL constraints are usually more efficient than Python constraints. When performance matters, always
+prefer SQL over Python constraints.
+
+Our real estate module is starting to look good. We added some business logic, and now we make sure
+the data is consistent. However, the user interface is still a bit rough. Let's see how we can
+improve it in the :ref:`next chapter <tutorials/getting_started/12_sprinkles>`.
+
+.. _PostgreSQL's documentation:
+.. _table_constraint:
+    https://www.postgresql.org/docs/12/ddl-constraints.html