TypeScript Power-Up: Transform Prisma JSON to Custom Types

A generator that changes the Prisma Client output to strongly type Json fields

// schema.prisma

generator client {
  provider = "prisma-client-js"
}

/// Always after the prisma-client-js generator
generator json {
  provider = "prisma-json-types-generator"
  // namespace = "PrismaJson"
  // clientOutput = "<finds it automatically>"
  // (./ -> relative to schema, or an importable path to require() it)
  // useType = "MyType"
  // In case you need to use a type, export it inside the namespace and we will add a index signature to it
  // (e.g.  export namespace PrismaJson { export type MyType = {a: 1, b: 2} }; will generate namespace.MyType["TYPE HERE"])
}

model Example {
  /// [MyType]
  normal Json

  /// [MyType]
  optional Json?

  /// [MyType]
  array Json[]

  /// [ComplexType]
  complex Json
}

Provide type definitions in a file that is part of the tsconfig.json#includes paths. For example:

// src/jsonTypes.ts

declare global {
  namespace PrismaJson {
    // you can use typical basic types
    type MyType = boolean;
    // or you can use classes, interfaces, object types, etc.
    type ComplexType = {
      foo: string;
      bar: number;
    };
  }
}

When you use your Prisma types in your application code, the JSON columns will now have the types provided under the PrismaJson namespace.

// src/example.ts

import type { Example } from '@prisma/client';

function myFunction(example: Example) {
  // example.normal   is now a boolean
  // example.optional is now a boolean | null
  // example.array    is now a boolean[]
  // example.complex  is now a { foo: string; bar: number }
}

How it works

⚠️ It just changes the declaration files of your generated client, no runtime code is affected!

By using the Typescript Compiler API, this generator parses the generated client's types AST and looks for Prisma.JsonValue types (or related) and replaces them with their corresponding type.

Some types are still json!

There are some complex json types like JsonFilter and JsonWithAggregatesFilter that, if typed, would impact the usability of the client. So, they are still json.

Usage with monorepos

If you're working with a monorepo, you must make sure the file containing the global definition for namespace PrismaJson is part of the runtime imports of your application. If you don't, the types will silently fall back to any.

// package1/src/jsonTypes.ts
declare global {
  namespace PrismaJson { /* ... */ }
}

// package1/src/client.ts
import { PrismaClient } from '@prisma/client';
import './jsonTypes.ts'; // if this is omitted, types are silently `any` outside of `package1`

export const client = new PrismaClient(...);
export { Example } from '@prisma/client';

Limitations

This project should be a temporary workaround (and possible solution) to https://github.com/prisma/prisma/issues/3219.

Json types inside type declarations won't work. (see https://github.com/prisma/prisma/issues/13726)

Download Details:

Author: prisma

Official Github: https://github.com/prisma/prisma-json-types-generator 

License: MIT

#typescript #prisma