How to populate a Sanity schema with read-only data?

Yes, you can populate a schema with read-only data in Sanity! There are several approaches depending on your use case:

Using the readOnly Property

The simplest way is to use the readOnly property on your field definitions. This makes fields visible but not editable:

{
  name: 'generatedId',
  type: 'string',
  readOnly: true
}

Conditional Read-Only Fields

You can also make fields read-only based on conditions using callback functions, as explained in the Conditional Fields documentation:

{
  name: 'publishedDate',
  type: 'datetime',
  readOnly: ({document}) => document?.status === 'published'
}

The callback receives parameters like parent, document, value, and currentUser, allowing you to create dynamic read-only logic.

Populating Read-Only Data

To actually populate these read-only fields with data, you have a few options:

1. Initial values - Set default values when documents are created:

{
  name: 'createdAt',
  type: 'datetime',
  readOnly: true,
  initialValue: () => new Date().toISOString()
}

2. Document actions - Use custom document actions to programmatically set values before saving

3. Mutations via API - Populate data through the Sanity API (mutations can write to read-only fields - the read-only restriction only applies to the Studio UI)

4. Sanity Functions - Use Sanity Functions to automatically populate fields when documents are created or updated through event handlers

The key thing to remember is that readOnly only affects the Studio editing interface - it doesn't prevent programmatic updates via the API. This gives you flexibility to populate data through automated processes while preventing manual editing by content creators.