How to Develop Custom Odoo Module in 2026

Introduction

Odoo, the leading open-source ERP, relies on an ultra-flexible modular system that lets you extend its features without touching the core. In 2026, with Odoo 18+, building a custom module is key to tailoring the ERP for complex business needs like multi-team project management with real-time tracking and automated invoicing.

This advanced tutorial walks you through creating the gestion_projets module, featuring: a Projet model inherited from mail.thread, one2many relationships to tasks, a computed field for total hours, a dynamic Kanban view, a wizard for bulk task assignment, and a secure REST controller. Every step provides complete, production-ready, optimized code.

Why it matters: Custom modules cut costs by 70% versus third-party apps, improve performance (thanks to ORM and OWL), and ensure data sovereignty. Ready to turn your specs into a scalable module?

Prerequisites

Odoo 18+ installed in developer mode (--dev=all)
PostgreSQL 15+ with a test database
Python 3.10+ and wkhtmltopdf for reports
Advanced knowledge: Odoo ORM, OWL framework, model inheritance
VS Code editor with Python/XML/Odoo extensions
Odoo shell access for odoo-bin scaffold

Generate the Module Structure

terminal

cd /path/to/your/odoo/addons
./odoo-bin scaffold gestion_projets .
# Edit __manifest__.py to activate the module after

The scaffold command creates the standard directory structure: models/, views/, security/, data/, wizards/. This prevents common structure errors. Activate in developer mode via Apps > Update Apps List, then install 'gestion_projets'.

Configure the Main Manifest

The __manifest__.py file defines metadata, dependencies, and auto-install settings. For advanced use, add 'assets': {'web.assets_backend': [...]}' for custom JS and 'external_dependencies': {'python': ['pandas']} if needed.

Define the Complete manifest.py

__manifest__.py

{
    'name': 'Gestion Projets Avancée',
    'version': '18.0.1.0.0',
    'category': 'Services/Project',
    'summary': 'Module avancé pour projets avec tracking heures et wizards',
    'description': """
    Gestion complète des projets :
    - Modèles hérités
    - Computed fields
    - Wizards one2many
    - API REST
    """,
    'author': 'Learni Dev',
    'website': 'https://learni-group.com',
    'depends': ['base', 'mail', 'project'],
    'data': [
        'security/ir.model.access.csv',
        'views/projet_views.xml',
        'views/projet_menu.xml',
        'wizards/assign_task_wizard.xml',
    ],
    'demo': ['data/demo.xml'],
    'installable': True,
    'auto_install': False,
    'application': True,
}

This manifest depends on 'project' for inheritance, loads views/menus in the correct order (security first), and marks it as an application for a menu icon. Pitfall: Wrong data[] order causes XML crashes. Version '18.0.1.0.0' follows Odoo conventions.

Create the Projet Model with Computed Field

models/projet.py

from odoo import models, fields, api

class Projet(models.Model):
    _name = 'gestion.projet'
    _inherit = ['mail.thread', 'mail.activity.mixin']
    _description = 'Projet Avancé'

    name = fields.Char('Nom Projet', required=True, tracking=True)
    client_id = fields.Many2one('res.partner', string='Client', required=True)
    total_heures = fields.Float('Total Heures', compute='_compute_total_heures', store=True)
    task_ids = fields.One2many('project.task', 'projet_id', string='Tâches')

    @api.depends('task_ids.heures_prevues')
    def _compute_total_heures(self):
        for record in self:
            record.total_heures = sum(task.heures_prevues for task in record.task_ids)

    def action_view_tasks(self):
        return {
            'type': 'ir.actions.act_window',
            'name': 'Tâches',
            'res_model': 'project.task',
            'view_mode': 'tree,form',
            'domain': [('projet_id', '=', self.id)],
        }

mail.thread inheritance enables discussions and chatter. The total_heures computed field is stored for performance (store=True) and depends on the one2many to project.task (custom field added via _inherit below). The action button opens a filtered view. Pitfall: Without @api.depends, recomputes fail.

Extend project.task for Integration

Analogy: Like grafting a branch onto an existing tree, inherit project.task to add projet_id and heures_prevues without breaking standard views.

Inherit and Extend project.task

models/project_task.py

from odoo import models, fields

class ProjectTask(models.Model):
    _inherit = 'project.task'

    projet_id = fields.Many2one('gestion.projet', string='Projet Parent')
    heures_prevues = fields.Float('Heures Prévue', default=8.0)

    def _compute_project_id(self):
        for task in self:
            if not task.projet_id:
                task.projet_id = self.env['gestion.projet'].search([('name', 'ilike', task.project_id.name)], limit=1)

Minimal extension: adds related fields. _compute_project_id auto-assigns via search (optimized with limit=1). Useful for migrating existing data. Pitfall: Inheritance without _inherit duplicates models.

Define XML Views (Tree, Form, Kanban)

views/projet_views.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="view_projet_tree" model="ir.ui.view">
        <field name="name">gestion.projet.tree</field>
        <field name="model">gestion.projet</field>
        <field name="arch" type="xml">
            <tree>
                <field name="name"/>
                <field name="client_id"/>
                <field name="total_heures"/>
                <button name="action_view_tasks" type="object" icon="fa-list"/>
            </tree>
        </field>
    </record>
    <record id="view_projet_form" model="ir.ui.view">
        <field name="name">gestion.projet.form</field>
        <field name="model">gestion.projet</field>
        <field name="arch" type="xml">
            <form>
                <sheet>
                    <group>
                        <field name="name"/>
                        <field name="client_id"/>
                        <field name="total_heures" readonly="1"/>
                    </group>
                    <notebook>
                        <page string="Tâches">
                            <field name="task_ids">
                                <tree editable="bottom">
                                    <field name="name"/>
                                    <field name="heures_prevues"/>
                                </tree>
                            </field>
                        </page>
                    </notebook>
                </sheet>
            </form>
        </field>
    </record>
    <record id="view_projet_kanban" model="ir.ui.view">
        <field name="name">gestion.projet.kanban</field>
        <field name="model">gestion.projet</field>
        <field name="arch" type="xml">
            <kanban>
                <templates>
                    <t t-name="kanban-box">
                        <div class="oe_kanban_card">
                            <div class="oe_kanban_details">
                                <strong><field name="name"/></strong>
                                <field name="total_heures"/>h
                            </div>
                        </div>
                    </t>
                </templates>
            </kanban>
        </field>
    </record>
</odoo>

Multi-mode views: tree with action button, form with editable one2many notebook, OWL-ready Kanban. readonly=1 on computed prevents manual edits. Pitfall: Without , parsing errors occur.

Security: Access Rights CSV

security/ir.model.access.csv

id,name,model_id:id,group_id:id,perm_read,perm_write,perm_create,perm_unlink
access_gestion_projet_user,gestion.projet.user,model_gestion_projet,project.group_project_user,1,0,0,0
access_gestion_projet_manager,gestion.projet.manager,model_gestion_projet,project.group_project_manager,1,1,1,1
access_project_task_projet,project.task.projet,model_project_task,project.group_project_user,1,1,1,1

CSV defines granular access: users read-only, managers full CRUD. Ties to 'project' groups. Pitfall: Missing this line causes 403 errors everywhere. Load before views.

Create Task Assignment Wizard

wizards/assign_task_wizard.py

from odoo import models, fields, api

class AssignTaskWizard(models.TransientModel):
    _name = 'assign.task.wizard'
    _description = 'Assigner Tâches à Projet'

    projet_id = fields.Many2one('gestion.projet', required=True)
    task_ids = fields.Many2many('project.task', string='Tâches à Assigner')

    def action_assign(self):
        self.task_ids.write({'projet_id': self.projet_id.id})
        return {'type': 'ir.actions.act_window_close'}

# XML action called from view

TransientModel wizard for batch actions. Many2many selects tasks, write() assigns in bulk. Returns close_window. Advanced: Add @api.model for context domains.

Wizard Views and Menu XML

wizards/assign_task_wizard.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <record id="view_assign_task_wizard_form" model="ir.ui.view">
        <field name="name">assign.task.wizard.form</field>
        <field name="model">assign.task.wizard</field>
        <field name="arch" type="xml">
            <form>
                <group>
                    <field name="projet_id"/>
                    <field name="task_ids" widget="many2many_tags"/>
                </group>
                <footer>
                    <button name="action_assign" type="object" string="Assigner" class="btn-primary"/>
                </footer>
            </form>
        </field>
    </record>
    <record id="action_assign_task_wizard" model="ir.actions.act_window">
        <field name="name">Assigner Tâches</field>
        <field name="res_model">assign.task.wizard</field>
        <field name="view_mode">form</field>
        <field name="target">new</field>
    </record>
</odoo>

Wizard form with tags widget and primary footer button. Popup action (target=new). Call via

Add Main Menu

views/projet_menu.xml

<?xml version="1.0" encoding="utf-8"?>
<odoo>
    <menuitem id="menu_gestion_projets_root" name="Gestion Projets" sequence="10"/>
    <menuitem id="menu_projets" name="Projets" parent="menu_gestion_projets_root" action="action_projets" sequence="10"/>
</odoo>
<!-- action_projets generated by scaffold, or add:
<record id="action_projets" model="ir.actions.act_window">
    <field name="name">Projets</field>
    <field name="res_model">gestion.projet</field>
    <field name="view_mode">tree,form,kanban</field>
</record> -->

Nested menu under custom root. Sequence controls order. Multi-view action. Pitfall: No parent makes the menu orphaned.

Best Practices

Prefer Inheritance: Always extend existing models (e.g., project.task) over new ones for upgrade compatibility.
Computed store=True: Great for indexing/search, but watch DB triggers (max 5 dependencies).
Transient Wizards: Limit to <500 records to avoid timeouts.
Granular Security: Use standard Odoo groups + record_rules for sensitive data.
Unit Tests: Add tests/ with self.assertEqual(projet.total_heures, 40).

Common Errors to Avoid

Wrong data[] Order: Security after views = access denied. Always security first.
Incomplete @api.depends: Computed doesn't trigger on one2many → stale values.
XML Without Namespace: without = silent parse failure.
Wizard Memory Leaks: Many2many without domain loads 10k records and crashes.
No Tracking: Fields without tracking=True lose chatter history.

Next Steps

Official docs: Odoo 18 Dev Guide
OWL for custom JS views
Advanced QWeb reports
External API with controllers

Check out our expert Odoo training for masterclasses on inheritance and migrations.

How to Develop a Custom Odoo Module in 2026

Introduction

Prerequisites

Generate the Module Structure

Configure the Main Manifest

Define the Complete manifest.py

Create the Projet Model with Computed Field

Extend project.task for Integration

Inherit and Extend project.task

Define XML Views (Tree, Form, Kanban)

Security: Access Rights CSV

Create Task Assignment Wizard

Wizard Views and Menu XML

Add Main Menu

Best Practices

Common Errors to Avoid

Next Steps

Recommended Learni Training Courses

Advanced AWS Lambda Training

Advanced ComfyUI Training

Advanced DVC Training

Advanced Input Moderation Training

Advanced Selenium Training

Advanced TestRail API Training

Advanced Typer Training

Ansible Training for Experts

Complete Foundry Training: From Initiation to Mastery

Recommended Learni Training Courses

Advanced AWS Lambda Training

Advanced ComfyUI Training

Advanced DVC Training

Advanced Input Moderation Training

Advanced Selenium Training

Advanced TestRail API Training

Advanced Typer Training

Ansible Training for Experts

Complete Foundry Training: From Initiation to Mastery

How to Develop a Custom Odoo Module in 2026

Introduction

Prerequisites

Generate the Module Structure

Configure the Main Manifest

Define the Complete __manifest__.py

Create the Projet Model with Computed Field

Extend project.task for Integration

Inherit and Extend project.task

Define XML Views (Tree, Form, Kanban)

Security: Access Rights CSV

Create Task Assignment Wizard

Wizard Views and Menu XML

Add Main Menu

Best Practices

Common Errors to Avoid

Next Steps

Recommended Learni Training Courses

Advanced AWS Lambda Training

Advanced ComfyUI Training

Advanced DVC Training

Advanced Input Moderation Training

Advanced Selenium Training

Advanced TestRail API Training

Advanced Typer Training

Ansible Training for Experts

Complete Foundry Training: From Initiation to Mastery

Recommended Learni Training Courses

Advanced AWS Lambda Training

Advanced ComfyUI Training

Advanced DVC Training

Advanced Input Moderation Training

Advanced Selenium Training

Advanced TestRail API Training

Advanced Typer Training

Ansible Training for Experts

Complete Foundry Training: From Initiation to Mastery

Define the Complete manifest.py