Related Fields Explained

Definition

A related field displays a value from a linked record on the current form. It "reaches through" a Many2one relationship to show information from the related record.

How It Works

graph LR
    SO[Sale Order] -- partner_id --> P[Customer]
    P -- country_id --> C[Country]
    SO -.->|related field| C

Example: Showing Customer's Country on Sales Order

Model	Field	Target
Sale Order	partner_id →	Customer (res.partner)
Customer	country_id →	Country (res.country)

A related field partner_country_id on Sale Order can directly show the customer's country without storing it!

Path: partner_id.country_id

Code Example

# On sale.order model
partner_country_id = fields.Many2one(
    'res.country',
    related='partner_id.country_id',
    string='Customer Country',
    store=False,  # Default - always reads from linked record
)

Stored vs Not Stored Related Fields

Feature	store=False (Default)	store=True
Value	Always live (reads from linked record)	Copied to database
Updates	Immediate when source changes	When source changes (via triggers)
Group By	No	Yes
Search/Filter	Limited	Full support
Performance	Can cause N+1 queries	Fast (indexed)
Stale Risk	Never stale	May become outdated

When to Use store=False (Default)

• You just want to display information on a form
• The linked value changes frequently
• You don't need to filter or group by it
• Database space is a concern

When to Use store=True

• You need to Group By this field in reports
• You need to filter or search by this field
• The field is displayed in list views (performance)
• You're building reports that query the database directly

The N+1 Query Problem

Performance Warning

If you have a non-stored related field and display it in a list view with 100 records:

• Odoo might need to make 100 separate database queries (one per record)
• This can slow down the page significantly

Solution: If the field is shown in list views, consider store=True

How to Detect N+1 Issues

Symptom	Likely Cause
List view loads slowly	Non-stored related fields in columns
Form view fast, list view slow	Too many computed/related fields in list
Timeout on large datasets	Unstored fields multiplying queries

Common Related Fields in Odoo

Where	Related Field	Path	Stored?
Sale Order Line	Product Category	product_id.categ_id	Depends
Invoice Line	Invoice State	move_id.state	Often Yes
Stock Move	Customer	picking_id.partner_id	Yes
Task	Project Manager	project_id.user_id	Depends
Employee	Department Manager	department_id.manager_id	Often No

Chained Related Fields

You can chain through multiple relationships:

# On project.task, show the project manager's country
manager_country_id = fields.Many2one(
    'res.country',
    related='project_id.user_id.partner_id.country_id',
    string='Manager Country',
)

Path: Task → Project → Manager (User) → Partner → Country

Chain Length

Longer chains = more potential for:

• Performance issues (more joins)
• Stale data (more points of change)
• Confusion (harder to understand the source)

Keep chains to 2-3 levels when possible.

The Stale Data Problem

When Stored Related Fields Don't Update

Stored related fields should update when the source changes, but sometimes they don't:

Common Causes:

1. Developer forgot to define proper dependencies
2. Data was imported directly to database
3. Batch update bypassed normal Odoo flows
4. Bug in the recomputation logic

Fix: Edit and save the record, or ask developer to run recomputation.

Related vs Computed Fields

Aspect	Related Field	Computed Field
Purpose	Fetch value from linked record	Calculate based on any logic
Syntax	related='path.to.field'	compute='_compute_method'
Flexibility	Limited to following relationships	Unlimited Python logic
Dependencies	Automatic from path	Must define with @api.depends
Best For	Displaying linked data	Calculations, aggregations

When to Use Each

Scenario	Use
Show customer's email on order	Related - just following a link
Calculate order total	Computed - summing line values
Show product category	Related - product_id.categ_id
Show days until deadline	Computed - date calculation
Display linked record's name	Related - simple path
Combine multiple fields	Computed - custom logic needed

Practical Examples

Example 1: Customer Information on Invoice

class AccountMove(models.Model):
    _inherit = 'account.move'

    # Related fields to show customer info
    customer_email = fields.Char(
        related='partner_id.email',
        string='Customer Email',
    )
    customer_phone = fields.Char(
        related='partner_id.phone',
        string='Customer Phone',
    )
    customer_country_id = fields.Many2one(
        'res.country',
        related='partner_id.country_id',
        string='Customer Country',
        store=True,  # Stored for reporting
    )

Example 2: Product Info on Order Line

class SaleOrderLine(models.Model):
    _inherit = 'sale.order.line'

    # Show product category for filtering
    product_categ_id = fields.Many2one(
        'product.category',
        related='product_id.categ_id',
        string='Product Category',
        store=True,  # Can group sales by category
    )
    product_type = fields.Selection(
        related='product_id.detailed_type',
        string='Product Type',
    )

Knowledge Check

Q1: Why can't you Group By a non-stored related field?

Answer: No database column exists

Group By uses SQL which requires a real column in the database. Non-stored related fields are calculated on-the-fly and have no column.

Q2: When should you add store=True to a related field?

Answer: When you need to filter, group, or search by it

Also consider storing it if the field appears in list views with many records (performance) or is used in reports.

Q3: What causes the N+1 query problem?

Answer: Non-stored related fields in list views

Each row in the list requires a separate query to fetch the related value, multiplying database calls.

Q4: A stored related field shows outdated data. What happened?

Answer: The field wasn't recalculated when the source changed

This can happen with direct database imports, batch updates, or missing dependency triggers. Fix by saving the record or running recomputation.

Q5: Related field vs computed field - which for showing linked customer name?

Answer: Related field

For simply displaying data from a linked record, use related. Computed is for calculations or custom logic.