Fix: Duplicate og:type when using extra_custom_props

[lucabfelix]

Problem:

When extra_custom_props is used to define og:type, the template ends up rendering the tag twice:

Once from extra_custom_props

Again from object_type or og_type

This results in duplicated tags, which breaks Open Graph validation and causes incorrect previews on platforms like Facebook and WhatsApp.

Example

Model configuration:

def get_extra_custom_props(self):
return [
('property', 'og:type', 'product'),
('property', 'product:price:amount', '100.00'),
]

_metadata = {
'object_type': 'article',
'extra_custom_props': 'get_extra_custom_props',
}

Current HTML output (incorrect):

Expected behavior

If og:type is already defined via extra_custom_props, it should not be rendered again from object_type or og_type.

Proposed solutions
Option 1: Prevent duplication in the template (preferred)

Add a helper method to detect whether og:type is already defined in extra_custom_props and skip rendering it again.

Template change

File: meta/templates/meta/meta.html

Before:

{% if meta.og_type %}{% og_prop 'type' meta.og_type %}
{% elif meta.object_type %}{% og_prop 'type' meta.object_type %}{% endif %}

After:

{# Render og:type only if it is not already defined in extra_custom_props #}
{% if not meta.has_og_type_in_custom_props %}
{% if meta.og_type %}{% og_prop 'type' meta.og_type %}
{% elif meta.object_type %}{% og_prop 'type' meta.object_type %}{% endif %}
{% endif %}

Helper method

File: meta/views.py

def has_og_type_in_custom_props(self):
"""
Returns True if og:type is defined in extra_custom_props.
"""
if not self.extra_custom_props:
return False

# Expected format: [('property', 'og:type', 'value'), ...]
for prop in self.extra_custom_props:
    if (
        len(prop) >= 3
        and prop[0] == 'property'
        and prop[1] == 'og:type'
    ):
        return True

return False

Option 2: Document the limitation (simpler alternative)

Since extra_custom_props is rendered before the default Open Graph tags, the documentation could explicitly state that object_type should not be used together with a custom og:type.

Documentation note

If you define og:type using extra_custom_props, do not also define object_type, as this will cause duplicated meta tags.

Incorrect example:

_metadata = {
'object_type': 'article',
'extra_custom_props': 'get_custom_props',
}

def get_custom_props(self):
return [
('property', 'og:type', 'product'),
]

Correct example:

_metadata = {
'extra_custom_props': 'get_custom_props',
}

def get_custom_props(self):
return [
('property', 'og:type', 'product'),
]

Testing
Case 1: extra_custom_props defines og:type
meta = Meta(
title='Test',
extra_custom_props=[
('property', 'og:type', 'product'),
]
)

assert meta.has_og_type_in_custom_props() is True

Case 2: Only object_type defined
meta = Meta(
title='Test',
object_type='article',
)

assert meta.has_og_type_in_custom_props() is False

Case 3: Both defined
meta = Meta(
title='Test',
object_type='article',
extra_custom_props=[
('property', 'og:type', 'product'),
]
)

extra_custom_props should take precedence

assert meta.has_og_type_in_custom_props() is True

[protoroto]

@lucabfelix Hi, thanks for opening this. Could you try to explain the use case of defining both object_type AND og:type in extra_custom_props? Because I see the problem, but I don't see why I would want to do that

[lucabfelix]

@protoroto

The og:type property is being rendered twice when it is defined in both extra_custom_props and object_type, which breaks Open Graph validation.

Use Case / Why This Happens:

When building e-commerce sites or product listings, developers need to:

Set og:type to "product" (instead of "article")

Add product-specific tags such as product:price:amount, product:price:currency, product:availability, etc.

Since product tags can only be added via extra_custom_props, it makes sense to define everything—including og:type—in the same place.

class Vehicle(ModelMeta, models.Model):
    price = models.DecimalField(max_digits=10, decimal_places=2)
    
    _metadata = {
        'object_type': 'article',  # Default from base model
        'extra_custom_props': 'get_custom_props',
    }
    
    def get_custom_props(self):
        return [
            ('property', 'og:type', 'product'),  # Overrides article → product
            ('property', 'product:price:amount', str(self.price)),
            ('property', 'product:price:currency', 'USD'),
            ('property', 'product:availability', 'in stock'),
        ]

Current Result

Expected Behavior

Only one og:type tag should be rendered, coming from extra_custom_props.

Why Not Just Use object_type?

Question: "Why not just set object_type='product'?"
Answer: Product-specific tags (product:price:*, product:availability, etc.) can only be added via extra_custom_props. For consistency and following the documentation pattern, developers define all product-related tags together.

The official docs show:

extra_custom_props = [
('property', 'og:type', 'music.song'), # ← Uses extra_custom_props for og:type
('property', 'music:duration', '3')
]

However, it does not mention that this conflicts with object_type.

Root Cause

The template meta/templates/meta/meta.html always renders og:type from object_type (lines 28-29), even if extra_custom_props has already defined it (line 10).

Suggested Fix

Add a check before rendering the default og:type:

{% if not meta.has_og_type_in_custom_props %}
{% if meta.og_type %}{% og_prop 'type' meta.og_type %}
{% elif meta.object_type %}{% og_prop 'type' meta.object_type %}{% endif %}
{% endif %}

Where has_og_type_in_custom_props() is a new method that checks whether og:type already exists in extra_custom_props.

To solve the problem I had to overwrite the meta.html template. But it would be good to correct it so that the user doesn't have to go through all the trouble I went through to figure it out.