JSON Maps: Key Questions Answered

Authored by Cameron Booth

Reviewed by Kelly Weaver

Last updated: February 11, 2026

Modern backends rarely stay static for long. You might start with a clean relational schema (tables, columns, constraints neatly defined), but as products evolve, so does the data. User preferences, feature flags, experiment metadata, integration configs, regional settings. Each new requirement adds more nullable columns, more migrations, and more schema churn just to support small, fast-moving features.

That’s where JSON maps (sometimes called JSON fields or JSON objects in databases like Postgres) come in.

A JSON map lets you store flexible, nested key-value data inside a single database column instead of constantly altering your database schema. Add a new setting? Drop in a new key. No migration required. For teams shipping quickly or iterating on AI-driven features and personalization, this can dramatically reduce friction in backend development.

But, there’s a cautionary note here: JSON maps can go wrong. Overuse them and you sacrifice query performance, indexing, type safety, and database-level constraints. Put core business logic or relationships inside JSON blobs and you’ll eventually run into painful refactors. The real skill is knowing when JSON is the right tool for dynamic metadata, and when a traditional relational column or join table is the safer, long-term choice.

In this practical guide, we’ll cover what JSON maps are, how they work in Xano, when to use them, when to avoid them, and how experienced backend engineers balance flexibility with schema discipline.

Let’s start with the basics.

What is a JSON map?

💡

What's a JSON map?

A JSON map is a key-value object stored in a single database field. Instead of creating separate columns for every piece of metadata, you store structured data as one JSON blob.

In Xano, this looks like a field with type JSON or object that contains something like:

{
  "theme": "dark",
  "notifications": true,
  "lastLoginDevice": "mobile"
}

That's it. It's just structured data in a single cell.

When should I use a JSON map instead of additional columns?

💡

When should I use it?

Use a JSON map when:

The data is optional or variable: Not every user needs every setting. A preferences map handles this gracefully without a dozen nullable columns.
The schema changes frequently: If you're iterating fast and don't want to run migrations every time you add a field, a JSON map lets you add keys on the fly.
The data doesn't need to be queried or filtered: If you're never going to run WHERE settings.theme = 'dark', storing it as JSON is cleaner.
You're storing nested or complex structures: Arrays of objects, deeply nested configs, anything that would be awkward to normalize into relational tables.

When should I NOT use a JSON map?

💡

When should I not use it?

Avoid JSON maps when:

You need to filter or sort by the data: database indexes don't work well with JSON internals. If you need to query SELECT * FROM users WHERE preferences->theme = 'dark', it’s not going to be a friendly query.
The data has strict validation requirements. Columns enforce types. JSON does not.
A typo in a key name at the Python layer won't throw an error until something breaks downstream.

The structure is stable and well-defined. If you know exactly what fields you need and they won't change, just use columns. That's what they're for.

How do I access values inside a JSON map in Xano?

💡

JSON maps in Xano

Xano treats JSON fields as first-class objects. Once you query a record, you can access nested values using dot notation in your function stack.

If your user record has a preferences field containing {"theme": "dark"}, you access it like:

$user.preferences.theme

Returns: "dark"

For arrays inside the JSON, you can use filters like |first or |last, or iterate with a foreach block.

What's the actual power of JSON maps?

💡

Best part of JSON maps

Simplicity.

You can add a new feature to your app. Let's say "user timezone preference". Just a simple property update on the JSON map.

No new columns added. No migration. No deploy. No downtime.

For a solo developer or a small team shipping fast, that friction reduction compounds. You're not waiting on schema changes. You're not coordinating migrations across environments. You just ship!

That said, this flexibility is a trade-off. You do lose type safety. You lose query performance on those fields. You lose the ability to enforce constraints at the database level.

The experienced move is knowing when to accept that trade-off and when to pay the cost of proper schema design.

Can I use JSON maps for relationships?

💡

JSON maps and relationships

Technically yes. Practically, be careful.

You could store an array of IDs in a JSON field:

{
  "favoriteClipIds": [42, 87, 103]
}

But now you can't use foreign key constraints. You can't cascade deletes. You can't easily join on those IDs without pulling the data into memory and iterating.

For loose, non-critical associations, such as "recently viewed items", this is fine. For anything structural, use a proper junction table.

What's the difference between JSON and object types in Xano?

💡

JSON vs. object types in Xano

In most practical contexts, they're interchangeable. Both store key-value data as JSON.

The distinction matters more at the input validation layer. If you define an input as object, Xano expects a dictionary. If you define it as JSON, it's more permissive and can accept arrays or other valid JSON structures.

When in doubt, use JSON for flexibility or object when you want to enforce dictionary structure.