Feature/ts type improvements

test/types/docArray.test.ts

@@ -1,5 +1,5 @@
 import { Schema, model, Document, Types, LeanDocument } from 'mongoose';
-import { expectError } from 'tsd';
+import { expectError, expectType } from 'tsd';
 
 const schema: Schema = new Schema({ tags: [new Schema({ name: String })] });
 
@@ -29,4 +29,29 @@ void async function main() {
   const _doc: LeanDocument<ITest> = await Test.findOne().orFail().lean();
   _doc.tags[0].name.substring(1);
   expectError(_doc.tags.create({ name: 'fail' }));
-}();
+}();
+
+// https://github.com/Automattic/mongoose/issues/10293
+async function gh10293() {
+  interface ITest {
+    name: string;
+    arrayOfArray: Types.Array<string[]>; // <-- Array of Array
+  }
+
+  const testSchema = new Schema<ITest>({
+    name: {
+      type: String,
+      required: true
+    },
+    arrayOfArray: [[String]]
+  });
+
+  const TestModel = model('gh10293TestModel', testSchema);
+
+  testSchema.methods.getArrayOfArray = function(this: InstanceType<typeof TestModel>): string[][] { // <-- function to return Array of Array
+    const test = this.toObject();
+
+    expectType<string[][]>(test.arrayOfArray);
+    return test.arrayOfArray; // <-- error here if the issue persisted
+  };
+}

test/types/lean.test.ts

@@ -1,5 +1,5 @@
-import { Schema, model, Document, LeanDocument, Types } from 'mongoose';
-import { expectError } from 'tsd';
+import { Schema, model, Document, LeanDocument, Types, BaseDocumentType, DocTypeFromUnion, DocTypeFromGeneric } from 'mongoose';
+import { expectError, expectNotType, expectType } from 'tsd';
 
 const schema: Schema = new Schema({ name: { type: 'String' } });
 
@@ -24,14 +24,18 @@ schema.method('testMethod', () => 42);
 const Test = model<ITest>('Test', schema);
 
 void async function main() {
-  const doc: ITest = await Test.findOne().orFail();
+  const doc = await Test.findOne().orFail();
 
   doc.subdoc = new Subdoc({ name: 'test' });
   doc.id = 'Hello';
 
   doc.testMethod();
 
-  const pojo = doc.toObject();
+  // Because ITest extends Document there is no good way for toObject
+  // to infer the type which doesn't add a high probability of a circular
+  // reference, so it must be specified here or else ITest above could be changed
+  // to `extends Document<number, {}, ITestBase>`
+  const pojo = doc.toObject<ITestBase>();
   expectError(await pojo.save());
 
   const _doc: ITestBase = await Test.findOne().orFail().lean();
@@ -103,4 +107,58 @@ async function gh11118(): Promise<void> {
   for (const doc of docs) {
     const _id: Types.ObjectId = doc._id;
   }
-}
+}
+
+async function getBaseDocumentType(): Promise<void> {
+  interface User {
+    name: string;
+    email: string;
+    avatar?: string;
+  }
+
+  type UserDocUnion = User & Document<Types.ObjectId>;
+  type UserDocGeneric = Document<Types.ObjectId, {}, User>;
+
+  // DocTypeFromUnion should correctly infer the User type from our unioned type
+  type fromUnion1 = DocTypeFromUnion<UserDocUnion>;
+  expectType<User>({} as fromUnion1);
+  // DocTypeFromUnion should give a "false" type if it isn't a unioned type
+  type fromUnion2 = DocTypeFromUnion<UserDocGeneric>;
+  expectType<false>({} as fromUnion2);
+  // DocTypeFromUnion should give a "false" type of it's an any
+  expectType<false>({} as DocTypeFromUnion<any>);
+
+  // DocTypeFromGeneric should correctly infer the User type from our Generic constructed type
+  type fromGeneric1 = DocTypeFromGeneric<UserDocGeneric>;
+  expectType<User>({} as fromGeneric1);
+  // DocTypeFromGeneric should give a "false" type if it's not a type made with Document<?, ?, DocType>
+  type fromGeneric2 = DocTypeFromGeneric<UserDocUnion>;
+  expectType<false>({} as fromGeneric2);
+  // DocTypeFromGeneric should give a "false" type of it's an any
+  expectType<false>({} as DocTypeFromGeneric<any>);
+
+  type baseDocFromUnion = BaseDocumentType<UserDocUnion>;
+  expectType<User>({} as baseDocFromUnion);
+
+  type baseDocFromGeneric = BaseDocumentType<UserDocGeneric>;
+  expectType<User>({} as baseDocFromGeneric);
+}
+
+async function getBaseDocumentTypeFromModel(): Promise<void> {
+  interface User {
+    name: string;
+    email: string;
+    avatar?: string;
+  }
+  const schema = new Schema<User>({});
+  const Model = model('UserBaseDocTypeFromModel', schema);
+  type UserDocType = InstanceType<typeof Model>;
+
+  type baseFromUserDocType = BaseDocumentType<UserDocType>;
+
+  expectType<User & { _id: Types.ObjectId }>({} as baseFromUserDocType);
+
+  const a: UserDocType = {} as any;
+
+  const b = a.toJSON();
+}

test/types/populate.test.ts

@@ -27,7 +27,7 @@ ParentModel.findOne({}).populate('child').orFail().then((doc: Parent & Document)
   } else {
     useChildDoc(child);
   }
-  const lean = doc.toObject();
+  const lean = doc.toObject<Parent>();
   const leanChild = lean.child;
   if (leanChild == null || leanChild instanceof ObjectId) {
     throw new Error('should be populated');

types/document.d.ts

@@ -5,6 +5,12 @@ declare module 'mongoose' {
   /** A list of paths to skip. If set, Mongoose will validate every modified path that is not in this list. */
   type pathsToSkip = string[] | string;
 
+  /**
+   * Generic types for Document:
+   * *  T - the type of _id
+   * *  TQueryHelpers - Object with any helpers that should be mixed into the Query type
+   * *  DocType - the type of the actual Document created
+   */
   class Document<T = any, TQueryHelpers = any, DocType = any> {
     constructor(doc?: any);
 
@@ -216,13 +222,11 @@ declare module 'mongoose' {
     set(value: any): this;
 
     /** The return value of this method is used in calls to JSON.stringify(doc). */
-    toJSON(options: ToObjectOptions & { flattenMaps: false }): LeanDocument<this>;
-    toJSON(options?: ToObjectOptions): FlattenMaps<LeanDocument<this>>;
-    toJSON<T = FlattenMaps<DocType>>(options?: ToObjectOptions): T;
+    toJSON<T = DocType>(options?: ToObjectOptions & { flattenMaps?: true }): FlattenMaps<LeanDocument<T>>;
+    toJSON<T = DocType>(options: ToObjectOptions & { flattenMaps: false }): LeanDocument<T>;
 
     /** Converts this document into a plain-old JavaScript object ([POJO](https://masteringjs.io/tutorials/fundamentals/pojo)). */
-    toObject(options?: ToObjectOptions): LeanDocument<this>;
-    toObject<T = DocType>(options?: ToObjectOptions): T;
+    toObject<T = DocType>(options?: ToObjectOptions): LeanDocument<T>;
 
     /** Clears the modified state on the specified path. */
     unmarkModified(path: string): void;

types/index.d.ts

@@ -1482,6 +1482,26 @@ declare module 'mongoose' {
 
   type ProjectionFields<DocType> = { [Key in keyof Omit<LeanDocument<DocType>, '__v'>]?: any } & Record<string, any>;
 
+  type _QueryManyForModel<T, ResultDoc, TQueryHelpers = {}> =
+    QueryWithHelpers<Array<ResultDoc>, ResultDoc, TQueryHelpers, T>;
+  type _QueryOneForModel<T, ResultDoc, TQueryHelpers = {}> =
+    QueryWithHelpers<ResultDoc, ResultDoc, TQueryHelpers, T>;
+
+  /**
+   * Helper type for getting a find Query type for a given Model (return of Model.find)
+   */
+  type QueryForModel<T extends Model<any>> =
+    T extends Model<infer MT, infer TQueryHelpers, infer TMethodsAndOverrides, infer TVirtuals> ?
+      _QueryManyForModel<MT, HydratedDocument<MT, TMethodsAndOverrides, TVirtuals>, TQueryHelpers>
+      : never;
+  /**
+   * Helper type for getting a findOne Query type for a given Model (return of Model.findOne)
+   */
+  type QueryOneForModel<T extends Model<any>> =
+  T extends Model<infer MT, infer TQueryHelpers, infer TMethodsAndOverrides, infer TVirtuals> ?
+    _QueryOneForModel<MT, HydratedDocument<MT, TMethodsAndOverrides, TVirtuals>, TQueryHelpers>
+    : never;
+
   class Query<ResultType, DocType, THelpers = {}, RawDocType = DocType> {
     _mongooseOptions: MongooseQueryOptions;
 
@@ -1583,7 +1603,7 @@ declare module 'mongoose' {
 
     /** Specifies a `$elemMatch` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     elemMatch(val: Function | any): this;
-    elemMatch(path: string, val: Function | any): this;
+    elemMatch<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$elemMatch']): this;
 
     /**
      * Gets/sets the error flag on this query. If this flag is not null or
@@ -1600,7 +1620,7 @@ declare module 'mongoose' {
 
     /** Specifies a `$exists` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     exists(val: boolean): this;
-    exists(path: string, val: boolean): this;
+    exists<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$exists']): this;
 
     /**
      * Sets the [`explain` option](https://docs.mongodb.com/manual/reference/method/cursor.explain/),
@@ -1680,18 +1700,18 @@ declare module 'mongoose' {
 
     /** Specifies a `$gt` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     gt(val: number): this;
-    gt(path: string, val: number): this;
+    gte<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$gt']): this;
 
     /** Specifies a `$gte` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     gte(val: number): this;
-    gte(path: string, val: number): this;
+    gte<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$gte']): this;
 
     /** Sets query hints. */
     hint(val: any): this;
 
     /** Specifies an `$in` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     in(val: Array<any>): this;
-    in(path: string, val: Array<any>): this;
+    in<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$in']): this;
 
     /** Declares an intersects query for `geometry()`. */
     intersects(arg?: any): this;
@@ -1707,11 +1727,11 @@ declare module 'mongoose' {
 
     /** Specifies a `$lt` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     lt(val: number): this;
-    lt(path: string, val: number): this;
+    lt<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$lt']): this;
 
     /** Specifies a `$lte` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     lte(val: number): this;
-    lte(path: string, val: number): this;
+    lte<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$lte']): this;
 
     /**
      * Runs a function `fn` and treats the return value of `fn` as the new value
@@ -1738,7 +1758,7 @@ declare module 'mongoose' {
 
     /** Specifies a `$mod` condition, filters documents for documents whose `path` property is a number that is equal to `remainder` modulo `divisor`. */
     mod(val: Array<number>): this;
-    mod(path: string, val: Array<number>): this;
+    mod<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$mod']): this;
 
     /** The model this query was created from */
     model: typeof Model;
@@ -1751,15 +1771,15 @@ declare module 'mongoose' {
 
     /** Specifies a `$ne` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     ne(val: any): this;
-    ne(path: string, val: any): this;
+    ne<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$ne']): this;
 
     /** Specifies a `$near` or `$nearSphere` condition */
     near(val: any): this;
-    near(path: string, val: any): this;
+    near<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$near']): this;
 
     /** Specifies an `$nin` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     nin(val: Array<any>): this;
-    nin(path: string, val: Array<any>): this;
+    nin<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$nin']): this;
 
     /** Specifies arguments for an `$nor` condition. */
     nor(array: Array<FilterQuery<DocType>>): this;
@@ -1795,7 +1815,7 @@ declare module 'mongoose' {
 
     /** Specifies a `$regex` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     regex(val: string | RegExp): this;
-    regex(path: string, val: string | RegExp): this;
+    regex<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$regex']): this;
 
     /**
      * Declare and/or execute this query as a remove() operation. `remove()` is
@@ -1848,7 +1868,7 @@ declare module 'mongoose' {
 
     /** Specifies an `$size` query condition. When called with one argument, the most recent path passed to `where()` is used. */
     size(val: number): this;
-    size(path: string, val: number): this;
+    size<KEY extends keyof FilterQuery<DocType>>(path: KEY, val: FilterQuery<DocType>[KEY]['$size']): this;
 
     /** Specifies the number of documents to skip. */
     skip(val: number): this;
@@ -2084,13 +2104,24 @@ declare module 'mongoose' {
   type TreatAsPrimitives = actualPrimitives |
   NativeDate | RegExp | symbol | Error | BigInt | Types.ObjectId;
 
+  // This will -- when possible -- extract the original type of the subdocument in question
+  type LeanSubdocument<T> = T extends (Types.Subdocument<Require_id<T>['_id']> & infer U) ? LeanDocument<U> : Omit<LeanDocument<T>, '$isSingleNested' | 'ownerDocument' | 'parent'>;
+
   type LeanType<T> =
     0 extends (1 & T) ? T : // any
       T extends TreatAsPrimitives ? T : // primitives
-        T extends Types.Subdocument ? Omit<LeanDocument<T>, '$isSingleNested' | 'ownerDocument' | 'parent'> : // subdocs
+        T extends Types.Subdocument ? LeanSubdocument<T> : // subdocs
           LeanDocument<T>; // Documents and everything else
 
-  type LeanArray<T extends unknown[]> = T extends unknown[][] ? LeanArray<T[number]>[] : LeanType<T[number]>[];
+  // Used only when collapsing lean arrays for ts performance reasons:
+  type LeanTypeOrArray<T> = T extends unknown[] ? LeanArray<T> : LeanType<T>;
+
+  type LeanArray<T extends unknown[]> =
+  // By checking if it extends Types.Array we can get the original base type before collapsing down,
+  // rather than trying to manually remove the old types. This matches both Array and DocumentArray
+    T extends Types.Array<infer U> ? LeanTypeOrArray<U>[] :
+      // If it isn't a custom mongoose type we fall back to "do our best"
+      T extends unknown[][] ? LeanArray<T[number]>[] : LeanType<T[number]>[];
 
   export type _LeanDocument<T> = {
     [K in keyof T]: LeanDocumentElement<T[K]>;
@@ -2100,18 +2131,46 @@ declare module 'mongoose' {
   // This way, the conditional type is distributive over union types.
   // This is required for PopulatedDoc.
   type LeanDocumentElement<T> =
-    T extends unknown[] ? LeanArray<T> : // Array
-      T extends Document ? LeanDocument<T> : // Subdocument
-        T;
+    0 extends (1 & T) ? T :// any
+      T extends unknown[] ? LeanArray<T> : // Array
+        T extends Document ? LeanDocument<T> : // Subdocument
+          T;
 
   export type SchemaDefinitionType<T> = T extends Document ? Omit<T, Exclude<keyof Document, '_id' | 'id' | '__v'>> : T;
 
+  // Helpers to simplify checks
+  type IfAny<IFTYPE, THENTYPE> = 0 extends (1 & IFTYPE) ? THENTYPE : IFTYPE;
+  type IfUnknown<IFTYPE, THENTYPE> = unknown extends IFTYPE ? THENTYPE : IFTYPE;
+
+  // tests for these two types are located in test/types/lean.test.ts
+  export type DocTypeFromUnion<T> = T extends (Document<infer T1, infer T2, infer T3> & infer U) ?
+    [U] extends [Document<T1, T2, T3> & infer U] ? IfUnknown<IfAny<U, false>, false> : false : false;
+
+  export type DocTypeFromGeneric<T> = T extends Document<infer IdType, infer TQueryHelpers, infer DocType> ?
+    IfUnknown<IfAny<DocType, false>, false> : false;
+
+  /**
+   * Helper to choose the best option between two type helpers
+   */
+  export type _pickObject<T1, T2, Fallback> = T1 extends false ? T2 extends false ? Fallback : T2 : T1;
+
+  /**
+   * There may be a better way to do this, but the goal is to return the DocType if it can be infered
+   * and if not to return a type which is easily identified as "not valid" so we fall back to
+   * "strip out known things added by extending Document"
+   * There are three basic ways to mix in Document -- "Document & T", "Document<ObjId, mixins, T>",
+   * and "T extends Document". In the last case there is no type without Document mixins, so we can only
+   * strip things out. In the other two cases we can infer the type, so we should
+   */
+  export type BaseDocumentType<T> = _pickObject<DocTypeFromUnion<T>, DocTypeFromGeneric<T>, false>;
+
   /**
    * Documents returned from queries with the lean option enabled.
    * Plain old JavaScript object documents (POJO).
    * @see https://mongoosejs.com/docs/tutorials/lean.html
    */
-  export type LeanDocument<T> = Omit<_LeanDocument<T>, Exclude<keyof Document, '_id' | 'id' | '__v'> | '$isSingleNested'>;
+  export type LeanDocument<T> = BaseDocumentType<T> extends Document ? _LeanDocument<BaseDocumentType<T>> :
+    Omit<_LeanDocument<T>, Exclude<keyof Document, '_id' | 'id' | '__v'> | '$isSingleNested'>;
 
   export type LeanDocumentOrArray<T> = 0 extends (1 & T) ? T :
     T extends unknown[] ? LeanDocument<T[number]>[] :