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Not all database functions and features of Prisma ORM's supported databases have a Prisma Schema Language equivalent. Refer to the [database features matrix](/orm/reference/database-features) for a complete list of supported features.

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## Native database functions

Prisma Schema Language supports several [functions](/orm/reference/prisma-schema-reference#attribute-functions) that you can use to set the default value of a field. The following example uses the Prisma ORM-level `uuid()` function to set the value of the `id` field:

```prisma
model Post {
  id String @id @default(uuid())
}
```

However, you can also use **native database functions** to define default values with [`dbgenerated(...)`](/orm/reference/prisma-schema-reference#dbgenerated) on relational databases (MongoDB does not have the concept of database-level functions). The following example uses the PostgreSQL `gen_random_uuid()` function to populate the `id` field:

```prisma
model User {
  id String @id @default(dbgenerated("gen_random_uuid()")) @db.Uuid
}
```

### When to use a database-level function

There are two reasons to use a database-level function:

- There is no equivalent Prisma ORM function (for example, `gen_random_bytes` in PostgreSQL).
- You cannot or do not want to rely on functions such `uuid()` and `cuid()`, which are only implemented at a Prisma ORM level and do not manifest in the database.

  Consider the following example, which sets the `id` field to a randomly generated `UUID`:

  ```prisma
  model Post {
    id String @id @default(uuid())
  }
  ```

  The UUID is _only_ generated if you use Prisma Client to create the `Post`. If you create posts in any other way, such as a bulk import script written in plain SQL, you must generate the UUID yourself.

### Enable PostgreSQL extensions for native database functions

In PostgreSQL, some native database functions are part of an extension. For example, in PostgreSQL versions 12.13 and earlier, the `gen_random_uuid()` function is part of the [`pgcrypto`](https://www.postgresql.org/docs/10/pgcrypto.html) extension.

To use a PostgreSQL extension, you must first install it on the file system of your database server.

In Prisma ORM versions 4.5.0 and later, you can then activate the extension by declaring it in your Prisma schema with the [`postgresqlExtensions` preview feature](/orm/prisma-schema/postgresql-extensions):

```prisma file=schema.prisma highlight=3,9;add showLineNumbers
generator client {
  provider        = "prisma-client"
  output          = "./generated"
  //add-next-line
  previewFeatures = ["postgresqlExtensions"]
}

datasource db {
  provider   = "postgresql"
  //add-next-line
  extensions = [pgcrypto]
}
```
```

In earlier versions of Prisma ORM, you must instead run a SQL command to activate the extension:

```sql
CREATE EXTENSION IF NOT EXISTS pgcrypto;
```

If your project uses [Prisma Migrate](/orm/prisma-migrate), you must [install the extension as part of a migration](/orm/prisma-migrate/workflows/native-database-functions) . Do not install the extension manually, because it is also required by the shadow database.

Prisma Migrate returns the following error if the extension is not available:

```
Migration `20210221102106_failed_migration` failed to apply cleanly to a temporary database.
Database error: Error querying the database: db error: ERROR: type "pgcrypto" does not exist
```

## Unsupported field types

Some database types of relational databases, such as `polygon` or `geometry`, do not have a Prisma Schema Language equivalent. Use the [`Unsupported`](/orm/reference/prisma-schema-reference#unsupported) field type to represent the field in your Prisma schema:

```prisma highlight=3;normal
model Star {
  id       Int                    @id @default(autoincrement())
  //highlight-next-line
  position Unsupported("circle")? @default(dbgenerated("'<(10,4),11>'::circle"))
}
```

The `prisma migrate dev` and `prisma db push` command will both create a `position` field of type `circle` in the database. However, the field will not be available in the generated Prisma Client.

## Unsupported database features

Some features, like SQL views or partial indexes, cannot be represented in the Prisma schema. If your project uses [Prisma Migrate](/orm/prisma-migrate), you must [include unsupported features as part of a migration](/orm/prisma-migrate/workflows/unsupported-database-features) .

---

# Table inheritance