mongoose-zod

A library which allows to author mongoose ("a MongoDB object modeling tool") schemas using zod ("a TypeScript-first schema declaration and validation library").

[!WARNING] This version and all the previous ones only support mongoose 6.x <6.8. Please consult peerDependencies section of package.json for more information.

Purpose

Declaring mongoose schemas in TypeScript environment has always been tricky in terms of getting the most out of type safety:

• You either have to first declare an interface representing a document in MongoDB and then create a schema corresponding to that interface (you get no type safety at all - even the official mongoose documentation says that "you as the developer are responsible for ensuring that your document interface lines up with your Mongoose schema")
• Or reverse things by using mongoose.InferSchemaType<typeof schema> which is far from ideal (impossible to narrow types, doesn't support TS enums, doesn't know about virtuals, has problems with fields named type, ...)
• Finally, you can use typegoose which is based on legacy decorators proposal and generally poorly infers types.

This library aims to solve many of the aforementioned problems utilizing zod as a schema authoring tool.

Installation

[!WARNING] Please do not forget to read the caveats section when you're done with the main documentation.

Install the package from npm:

npm i mongoose-zod
pnpm i mongoose-zod
yarn add mongoose-zod

Usage

Firstly, you may want to perform a set up. Here you can pass your own z instance (you can get "our" z by importing z from this package) or opt out of adding new functions to zod prototype altogether. Please only call the setup function at the entrypoint of your application.

import {setup, z: theirZ} from 'mongoose-zod';
import {z: myZ} from 'zod';

setup({z: myZ}); // mongoose-zod will add new functions to the prototype of `myZ`
// NB: this is only an example of calling `setup` multiple times. In reality,
// all subsequent `setup` calls will be ignored!
setup({z: null}); // mongoose-zod will NOT add new functions to the prototype of zod altogether
setup(); // Equivalent to the default behaviour (also equivalent to `setup({z: theirZ})`).

Define the schema and use it as follows:

import {z} from 'zod';
import {genTimestampsSchema, toMongooseSchema, mongooseZodCustomType} from 'mongoose-zod';

export const userZodSchema = z
  .object({
    // Sub schema
    info: z.object({
      // Define type options like this (NOT recommended - better to use `typeOptions` passed to `.mongoose()` - see FAQ)
      // [instead `.mongooseTypeOptions()`, you may use `addMongooseTypeOptions` if you opt out of extending zod prototype]
      nickname: z.string().min(1).mongooseTypeOptions({unique: true}),
      birthday: z.tuple([
        z.number().int().min(1900),
        z.number().int().min(1).max(12),
        z.number().int().min(1).max(31),
      ]),
      // Unlike mongoose, arrays won't have an empty array `[]` as a default value!
      friends: z.number().int().min(1).array().optional(),
      // Making the field optional
      status: z.enum(['😊', '😔', '🤔']).optional(),
      // Use this function to use special (Buffer, ObjectId, ...) and custom (Long, ...) types
      avatar: mongooseZodCustomType('Buffer'),
    }),
    // Default values set with zod's .default() are respected
    regDate: z.date().default(new Date()),
  })
  // Schema merging supported natively by zod. We make use of this feature
  // by providing a schema generator for creating type-safe timestamp fields
  .merge(genTimestampsSchema('crAt', 'upAt'))
  // Define schema options here:
  // [instead `.mongoose()`, you may use `toZodMongooseSchema` if you opt out of extending zod prototype]
  .mongoose({
    schemaOptions: {
      collection: 'users',

      // Full type safety in virtuals, as well as in statics, methods and query methods
      virtuals: {
        bday: {
          get() {
            const [y, m, d] = this.info.birthday;
            return new Date(y, m - 1, d);
          },
          set(d: Date) {
            this.info.birthday = [d.getFullYear(), d.getMonth() + 1, d.getDate()];
          },
        },
      },

      statics: { ... },
      methods: { ... },
      query: { ... },
    },

    // Ability to override type schema options
    typeOptions: {
      upAt: {
        index: false,
      },
    },
  });

const UserSchema = toMongooseSchema(userZodSchema, { ...options... });

const User = M.model('User', UserSchema);

const user = new User().toJSON();

Result:

toMongooseSchema accepts some options in the optional second parameter that control the unknown keys handling and automatic plugin registration. You can read more on this in the next section. Worth nothing that you may set these options globally, in the setup call.

Additional safety measures

Since the overarching goal of this library is to simplify working with mongoose schemas, one way to accomplish that is to also get rid of non-obvious, too permissive or annoying behaviour of mongoose. That's why by default:

• Arrays won't have an empty array [] set as a default value (it is undefined instead, but you will be able to override it).
• Root schema won't have an id virtual.
• Empty objects won't be removed from documents upon saving (minimize is set to false).
• Sub schemas (which are automatically created for fields with ZodObject type) won't be set an _id property.
• All array field will not allow casting of non-array values to arrays.
• Casting is also disabled for types like number, string, boolean and date and cannot be re-enabled (WARNING: doesn't currently work in array of objects).
• Schemas will have strict option set to throw instead of just true by default (throws if a document has extraneous fields).
• For all the fields of Buffer type an actual Buffer instance (and not mongodb's Binary) will be returned after using .lean() (see here why it's not the case in mongoose). This is achieved by defining a getter on such fields which pulls out a buffer from a Binary. Such getters can be overridden, and it is also exported under bufferMongooseGetter name.

But that's not all.

Type-safe validate and required options

You can use special validate and required type options alternatives we provide, mzValidate and mzRequired respectively. In contrast to their vanilla counterparts, they not only guarantee type safety, but their runtime behaviour matches the declared types. They will actually have this set to undefined when run during update operation (click here for mongoose docs on this) and mzValidate will have a proper type of its argument.

⚠️ Some warnings:

• this type is still going to be any when used with .mongooseTypeOptions. See the FAQ for more info on the best way of defining type options in general.
• You can't define validate and mzValidate (and the other one) simultaneously. The error will be thrown upon schema creation if both say required and mzRequired are present.
• Schema.validate() calls that register additional validators won't be type safe.

Certain plugins are automatically added to schemas if found

If the following plugins are installed, they will be automatically registered on every schema you create with mongoose-zod:

• mongoose-lean-virtuals
• mongoose-lean-defaults
• mongoose-lean-getters

You can opt out of this behaviour when creating a schema in the following manner:

const Schema = toMongooseSchema( ... , {
  disablePlugins: {
    leanVirtuals: true,
    leanDefaults: true,
    leanGetters: true,
  } | true,
});

Or set the options globally in the setup call (see above for more info on setup):

setup({
  ...,
  defaultToMongooseSchemaOptions: {disablePlugins: true, unknownKeys: 'strip'},
});

mongoose-zod is smart enough to gradually re-enable certain plugins if all were disabled globally. That means that with this global config, if you specify say disablePlugins: {leanVirtuals: false} for a certain schema, only mongoose-lean-virtuals plugin will be added to this schema.

The most intriguing thing is that you won't have to explicitly make them work on every .lean() call:

const user = await User.findOne({ ... }).lean();
// is equivalent to (if respective plugins are installed):
const user = await User.findOne({ ... }).lean({
  virtuals: true,
  defaults: true,
  getters: true,
  versionKey: false, // <-- Bonus
});

Note that versionKey: false is also always set regardless of plugins!

You can override certain options if you wish:

// If `mongoose-lean-getters` is installed, `getters: true` will still be implicitly set
const user = await User.findOne({ ... }).lean({ virtuals: false, anyOtherOption: true });

Notes:

• If you pass to .lean() anything but an object or null, these options won't be set.
• The described behaviour is achieved by defining a custom lean query method. If you also define a query method with lean name, it will override our version.

More on schema's strict option

By default mongoose-zod sets strict option to throw instead of true for a root schema and sub schemas. You can control this behaviour by changing unknownKeys option when creating a schema:

• unknownKeys: 'throw' is an alias for the default behaviour.
• unknownKeys: 'strip' makes sure throw is always set to true and cannot be overridden via zod schemas.
• unknownKeys: 'strip-unless-overridden' allows to override this schema option with zod's .passthrough() and strip().
• You can always override strict option value by redefining it in the schema options.

FAQ

What is the recommended way of defining type options?

The example above demonstrates that there are three ways of defining type options for the field: .mongooseTypeOptions({ ... }), .mongoose({typeOptions: { ... }}) or by using a stand-alone function addMongooseTypeOptions({ ... }). There's a good reason why these options exist and here is the recipe for their correct usage:

• Use .mongooseTypeOptions in shared schemas you're planning to merge/extend/modify (because after you've used .mongoose() you won't be able to do any of these operations).
• Consequently, use .mongoose elsewhere. It's less verbose and this way you separate field type declarations from field metadata like indexes, custom validators, etc. Moreover, only here type safety is fully available for some custom type options we provide.
• If you opt out of extending the zod prototype, use addMongooseTypeOptions.
• Keep in mind that options defined with addMongooseTypeOptions override the ones defined in .mongooseTypeOptions, and the ones defined in .mongoose take precedence of both of these two methods.

How to obtain a schema type and what to do with it?

You have two options:

• Infer zod schema type as follows: type SchemaType = z.infer<typeof zodSchema>.
• Infer mongoose schema type as follows: type SchemaType = mongoose.InferSchemaType<typeof MongooseSchema>.

The good thing is they both should be equal! Then you can use it say in your frontend code by using TypeScript's type only import to make sure no actual code is imported, only types:

// user.model.ts (backend):
...
const userZodSchema = z.object({ ... }).mongoose();
const UserSchema = toMongooseSchema(userZodSchema);
...
export type IUser = z.infer<typeof userZodSchema>;
// OR
export type IUser = mongoose.InferSchemaType<typeof UserSchema>;
...

// somewhere on frontend, notice "import type":
import type {IUser} from '<...>/user.model';
...

How to use special types like Buffer, ObjectId, Decimal128 or custom ones like Long?

Use a stand-alone function called mongooseZodCustomType.

import {z} from 'zod';
import {mongooseZodCustomType} from 'mongoose-zod';

const zodSchema = z.object({
  refs: mongooseZodCustomType('ObjectId').array(),
  data: mongooseZodCustomType('Buffer').optional(),
}).mongoose();

Don't we still have type safety for options like alias and timestamps?

Yes, we don't. Instead timestamps, merge your schema with a timestamps schema generator exported under the genTimestampsSchema name.

Instead alias, simply use a virtual (which is what mongoose aliases actually are).

What zod types are supported and how are they mapped to mongoose types?

¹ Enums with mixed values, e.g. with both string and numbers. Also see TypeScript docs.
² Has nothing to do with mongoose discriminators.
³ A class provided with mongooseZodCustomType() or Mixed instead.

• Types named MongooseZodBaseClass are custom types inherited from BaseClass with the only function overloaded being cast which disables casting altogether.
• If the zod type is not supported, a MongooseZodError error will be thrown upon schema creation.
• The same error will be thrown when the zod type as a whole is supported, but this specific case it describes is not. Some examples: Infinity number literal, bigint literal, empty enums.

How do I access the data set by .mongooseTypeOptions/.mongoose?

We expose MongooseTypeOptionsSymbol and MongooseSchemaOptionsSymbol symbols respectively that you can use to get to the data set with the respective methods in the following way:

const zodSchema = z.object({ ... }).mongoose({ ... });
const schemaOptions = zodSchema._def[MongooseSchemaOptionsSymbol];

⚠️ Caveats ⚠️

I get the error: .mongooseTypeOptions/.mongoose is not a function

It is due to that mongoose-zod extends the prototype of z to chain the functions you are experiencing trouble with. This error indicates that zod extensions this package adds have not been registered yet. This may happen when (1) you've used either of these methods but haven't imported anything from mongoose-zod (2) you're (accidentally) using a different zod or mongoose instance or version in your code. In the first case the best strategy would probably be to import the package at the entrypoint of your application like that:

import 'mongoose-zod';
...

You can also use the z that is included in mongoose-zod instead of the z from zod directly to be sure you have the correct z reference:

import {z} from 'mongoose-zod';

...
const userZodSchema = z.object({ ... }).mongoose();
const UserSchema = toMongooseSchema(userZodSchema);

When this is not possible in your use case, or you prefer a function over a prototype extend you can use the following:

import {addMongooseTypeOptions, toZodMongooseSchema} from './extensions';

const zodSchema = toZodMongooseSchema(z.object({
  nickname: addMongooseTypeOptions(z.string().min(1), {unique: true}),
  friends: z.number().int().min(1).array().optional(),
}))

instead of

const zodSchema = z.object({
  nickname: z.string().min(1).mongooseTypeOptions({unique: true}),
  friends: z.number().int().min(1).array().optional(),
}).mongoose();

Be careful when using shared schemas with .mongooseTypeOptions/.mongoose

If the schema of multiple fields is structurally the same, we highly recommend that you do NOT create a shared schema. Instead, create a factory, because the data attached with .mongooseTypeOptions/.mongoose will also be shared, and that's not always what you want.

// ❌ DON'T do:
const PositiveInt = z.number().int().min(1);
... // somewhere in the schema definition:
  userId: PositiveInt.mongooseTypeOptions({ index: true}),
  country: PositiveInt, // surprise, this field will have "index: true" as well!
...

// ✅ do:
const PositiveInt = () => z.number().int().min(1);
...
  userId: PositiveInt().mongooseTypeOptions({ index: true}),
  country: PositiveInt(),
...

Prefer ZodRecord over ZodMap

We highly recommend that you do not use ZodMap. Map values are problematic to serialize and they're stored as BSON objects anyway, therefore now can be safely replaced with ZodRecord. (Well, actually, prefer arrays over records, unless you really need them).

ZodObject as a member of union is not treated like a sub schema

It means that no default schema options will be set (because mongoose's sub schema won't be created in the first place) for a ZodObject in a ZodUnion. For example this results in unknown keys are not being removed. You must use zod's .strict()/.passthrough() methods to control this behaviour.

Values in an array of objects still casted by mongoose

Unfortunately I haven't found a way yet to disable casting in this case. PR's and presenting your ideas on how to achieve that are more than welcome!

That's an illustration on what is meant here:

const Schema = toMongooseSchema(
  ...
  arrayOfObjects: z.object({a: z.string()}).array()
  ...
);
const Model = mongoose.model('model_name', Schema);
const doc = new Model({ ..., arrayOfObjects: [{a: ''}]}, ...);
// becomes :(
{ ..., arrayOfObjects: [{a: undefined}], ...}

License

See LICENSE.md.