The free document field allows to link a document of any collection.
Usage example
This field can be used in a Shopping list collection.
![Shopping list](/img/screen/shopping-collections.png)
![](/img/iphone-14-pro.png)
The Shopping list can link documents of different collections (Books, Games, Clothing).
![Shopping list](/img/screen/shopping-list-field.png)
![](/img/iphone-14-pro.png)
It has an Item field (free document) and a Price field (formula).
![Shopping list](/img/help/shopping-list-price-formula.png)
The Price formula allows to read the price of the linked document. The formula contains the Value by attribute function, which allows to get a field's value of a free document (Item in our case).
Since each collection (Books, Games, Clothing) has its own Price field, you can use attributes to universally identify it.
![Field attributes](/img/screen/free-doc-attributes-1.png)
![](/img/iphone-14-pro.png)
Open the Clothing collection → Edit the Price field → Tap on Attributes.
![Field attributes](/img/screen/free-doc-attributes-2.png)
![](/img/iphone-14-pro.png)
Add a Price attribute.
You should add the Price attribute for each collection you want to support in the Shopping list.
![Shopping list](/img/screen/shopping-list.png)
![](/img/iphone-14-pro.png)
Here's how the Shopping list looks like after configuring it.