Chapter 13: Inheritance¶
A powerful aspect of Flectra is its modularity. A module is dedicated to a business need, but modules can also interact with one another. This is useful for extending the functionality of an existing module. For example, in our real estate scenario we want to display the list of a salesperson’s properties directly in the regular user view.
But before going through the specific Flectra module inheritance, let’s see how we can alter the behavior of the standard CRUD (Create, Retrieve, Update or Delete) methods.
Goal: at the end of this section:
It should not be possible to delete a property which is not new or canceled.
When an offer is created, the property state should change to ‘Offer Received’
It should not be possible to create an offer with a lower price than an existing offer
In our real estate module, we never had to develop anything specific to be able to do the standard CRUD actions. The Flectra framework provides the necessary tools to do them. In fact, such actions are already included in our model thanks to classical Python inheritance:
from flectra import fields, models class TestModel(models.Model): _name = "test.model" _description = "Test Model" ...
These methods (and any other method defined on
Model) can be extended to add
specific business logic:
from flectra import fields, models class TestModel(models.Model): _name = "test.model" _description = "Test Model" ... @api.model def create(self, vals): # Do some business logic, modify vals... ... # Then call super to execute the parent method return super().create(vals)
In Python 3,
super() is equivalent to
super(TestModel, self). The latter may be necessary
when you need to call the parent method with a modified recordset.
It is very important to always call
super()to avoid breaking the flow. There are only a few very specific cases where you don’t want to call it.
Make sure to always return data consistent with the parent method. For example, if the parent method returns a
dict(), your override must also return a
Add business logic to the CRUD methods.
Prevent deletion of a property if its state is not ‘New’ or ‘Canceled’
unlink() and remember that
self can be a recordset
with more than one record.
At offer creation, set the property state to ‘Offer Received’. Also raise an error if the user tries to create an offer with a lower amount than an existing offer.
property_id field is available in the
vals, but it is an
estate.property object, use
Reference: the documentation related to this topic can be found in Inheritance and extension.
In our real estate module, we would like to display the list of properties linked to a salesperson
directly in the Settings / Users & Companies / Users form view. To do this, we need to add a field to
res.users model and adapt its view to show it.
Flectra provides two inheritance mechanisms to extend an existing model in a modular way.
The first inheritance mechanism allows modules to modify the behavior of a model defined in an another module by:
adding fields to the model,
overriding the definition of fields in the model,
adding constraints to the model,
adding methods to the model,
overriding existing methods in the model.
The second inheritance mechanism (delegation) allows every record of a model to be linked to a parent model’s record and provides transparent access to the fields of this parent record.
In Flectra, the first mechanism is by far the most used. In our case, we want to add a field to an existing model, which means we will use the first mechanism. For example:
from flectra import fields, models class InheritedModel(models.Model): _inherit = "inherited.model" new_field = fields.Char(string="New Field")
A practical example where two fields are added to a model can be found here.
By convention, each inherited model is defined in its own Python file. In our example, it would be
Add a field to Users.
Add the following field to
One2many inverse of
Add a domain to the field so it only lists the available properties.
Now let’s add the field to the view and check that everything is working well!
Reference: the documentation related to this topic can be found in Inheritance.
Goal: at the end of this section, the list of available properties linked to a salesperson should be displayed in their user form view
Instead of modifying existing views in place (by overwriting them), Flectra provides view inheritance where children ‘extension’ views are applied on top of root views. These extension can both add and remove content from their parent view.
An extension view references its parent using the
Instead of a single view, its
arch field contains a number of
xpath elements that select and alter the content of their parent view:
<record id="inherited_model_view_form" model="ir.ui.view"> <field name="name">inherited.model.form.inherit.test</field> <field name="model">inherited.model</field> <field name="inherit_id" ref="inherited.inherited_model_view_form"/> <field name="arch" type="xml"> <!-- find field description and add the field new_field after it --> <xpath expr="//field[@name='description']" position="after"> <field name="new_field"/> </xpath> </field> </record>
An XPath expression selecting a single element in the parent view. Raises an error if it matches no element or more than one
Operation to apply to the matched element:
xpath’s body to the end of the matched element
replaces the matched element with the
xpath’s body, replacing any
$0node occurrence in the new body with the original element
xpath’s body as a sibling before the matched element
xpaths’s body as a sibling after the matched element
alters the attributes of the matched element using the special
attributeelements in the
When matching a single element, the
position attribute can be set directly
on the element to be found. Both inheritances below have the same result.
<xpath expr="//field[@name='description']" position="after"> <field name="idea_ids" /> </xpath> <field name="description" position="after"> <field name="idea_ids" /> </field>
An example of a view inheritance extension can be found here.
Add fields to the Users view.
property_ids field to the
base.view_users_form in a new notebook page.
Tip: an example an inheritance of the users’ view can be found here.
Inheritance is extensively used in Flectra due to its modular concept. Do not hesitate to read the corresponding documentation for more info!
In the next chapter, we will learn how to interact with other modules.