How to Use Notion Relation Property With Default Value Per Sub-Type

You want a Notion relation property to automatically show a default value based on a sub-type of the source item. For example, when you create a new task in a Project database, you want a related project manager to fill in automatically depending on whether the task is a Bug or a Feature. Notion does not offer a built-in way to set a default value per sub-type on a relation property. This article explains how to achieve this using a combination of select properties, rollups, and formulas, without relying on third-party tools or complex automations.

How a Relation Property Works and Why Default Values Depend on Sub-Type

A Notion relation property links two databases together. When you create a new item in the source database, the relation property remains empty until you manually select a value from the target database. Notion does not natively support conditional default values for relation properties. This limitation becomes visible when you have items that belong to different sub-types and each sub-type requires a different default relation.

To solve this, you need three databases and three property types. The source database holds the items with a sub-type select property. A lookup database stores the default relation values for each sub-type. A formula in the source database reads the sub-type, looks up the appropriate default from the lookup database via a rollup, and sets the relation property to that value. The formula cannot directly write to a relation property, but you can use a rollup to display the default relation and then manually apply it.

Steps to Set Up a Default Relation Value Per Sub-Type

This method uses a helper database and a formula to show the correct default relation. The final step requires you to click a button or use a checkbox to apply the default to the relation property.

1. Create the source database with a sub-type select property
   Create a new database (for example, Tasks). Add a Select property named Sub-Type with options Bug, Feature, and Improvement. Add a Relation property named Default Manager that links to a target database (for example, Managers).
2. Create a lookup database for default values
   Create a new database named Defaults. Add a Select property named Sub-Type with the same options as the source database. Add a Relation property named Manager that links to the Managers database. In the Defaults database, add one item for each sub-type. For each item, select the correct manager from the Managers database. For example, the Bug item has Manager set to Alice, the Feature item has Manager set to Bob, and the Improvement item has Manager set to Charlie.
3. Add a rollup property in the source database
   In the Tasks database, add a Rollup property. Name it Default Manager Rollup. Configure it to roll up from the Defaults database. Set the Relation property to link to Defaults. Add a condition that the Sub-Type in Tasks matches the Sub-Type in Defaults. This condition is not directly available in the rollup configuration, so you must use a formula to filter manually. Instead, create a formula property that returns the correct default manager based on the Sub-Type.
4. Create a formula to return the default manager name
   In the Tasks database, add a Formula property named Default Manager Name. Use the following formula:
   if(prop("Sub-Type") == "Bug", "Alice", if(prop("Sub-Type") == "Feature", "Bob", "Charlie"))
   Replace the names with the actual manager names from the Managers database. This formula outputs the name of the default manager for the current sub-type.
5. Create a lookup relation from the formula output
   This step is not possible with formulas alone. Instead, use a workaround: create a checkbox property named Apply Default. Create a button property (Notion button) that when clicked, sets the Default Manager relation to the value indicated by the Default Manager Name formula. To do this, you need a third-party automation like Notion Automations or a connected tool. If you do not have access to buttons, you can manually set the Default Manager relation each time you create a new item by looking at the formula output.
6. Automate with a button property (optional)
   If you have a Notion workspace with button support, add a Button property to the Tasks database. Configure the button to edit the Default Manager property. Set the edit action to replace the value with the result of the Default Manager Name formula. Notion buttons can reference formula outputs when setting relation properties. This step automates the assignment.

Common Mistakes and Limitations When Setting Default Relations by Sub-Type

Formula cannot directly populate a relation property

A Notion formula property can output text, numbers, dates, or booleans, but it cannot output a relation value. You must use a button or manual action to transfer the formula result into the relation property. If you try to use a rollup that points to the formula, it still returns a text name, not a relation link.

Rollup conditions are limited to direct relations

Notion rollups cannot filter based on a property in the source database. To pull the correct default, you must use a formula to derive the default manager name, then use that name in a button action. A rollup that links to the Defaults database will return all managers, not just the one matching the sub-type.

Button actions require a specific relation value

When configuring a button to set a relation property, the button must know the exact page from the target database. You cannot use a formula that returns a name to directly set a relation. Instead, you can use a lookup table that maps names to relation IDs. This adds complexity. A simpler approach is to use a select property in the source database that mirrors the sub-type and then use a button to set the relation based on that select property.

Manual fallback is time-consuming for many items

If you have dozens of new items daily, manually checking a formula output and setting the relation property becomes inefficient. Consider using a third-party automation tool like Zapier or Make to watch for new items in the Tasks database and set the relation based on the sub-type. These tools can read the sub-type, query the Defaults database, and update the relation property automatically.

Manual Workflow vs Automated Button vs Third-Party Automation

Item	Manual Workflow	Button Automation	Third-Party Automation
Setup complexity	Low	Medium	High
Time per new item	10-20 seconds	1 click	0 seconds
Requires external tools	No	No	Yes
Risk of human error	High	Low	Low
Works in all Notion plans	Yes	Yes (button property available on Plus and higher)	Yes

You can now set a default relation value that changes based on the sub-type of a database item. Use the formula property to display the correct default name, then apply it with a button or manually. For high-volume workflows, connect Notion to an automation service to eliminate manual steps. The key limitation is that Notion formulas cannot write to relation properties directly, so you must always use an intermediary action like a button or an external script.