nestjs-mongoose-ref-issue-reproduction

This repository is a reproduction of an issue I am facing with @nestjs/mongoose, where when using a dynamic ref in a (NestJS Mongoose) schema, the ref function appears to be resolved at the time the schema is created, instead of at runtime.

In this reproduction, I am using a dynamic ref inside an array of embedded discriminators. This is so that I can define various article section types that can be embedded inside an article document.

This is an excerpt from src/article/article-section.schema.ts using @nestjs/mongoose demonstrating the value of this inside the ref function:

@Prop({
  type: [
    {
      type: mongoose.Schema.Types.ObjectId,
      ref() {
        console.log(this); // => {
                           // =>   type: [Function: SchemaObjectId] {
                           // =>     schemaName: 'ObjectId',
                           // =>     defaultOptions: {},
                           // =>     get: [Function (anonymous)],
                           // =>     set: [Function: set],
                           // =>     setters: [],
                           // =>     _checkRequired: [Function (anonymous)],
                           // =>     _cast: [Function: castObjectId],
                           // =>     cast: [Function: cast],
                           // =>     _defaultCaster: [Function (anonymous)],
                           // =>     checkRequired: [Function (anonymous)]
                           // =>   },
                           // =>   ref: [Function: ref]
                           // => }
        return this.embedType;
      },
    },
  ],
  required: true,
})

In a regular Mongoose schema, the ref function would be resolved at runtime, allowing for dynamic references.

Proof of work

This repository adopts the regular NestJS structure for separation of concerns, with the following structure:

• The files <module>/<module>.schema.ts contain regular NestJS Mongoose schema definitions.
• The files <module>/<module>.model.ts contain plain Mongoose schema & model definitions.

Two E2E tests, running the same test/run-mongoose-tests.ts assertions verify that the issue is present in the NestJS Mongoose schema, but not in the plain Mongoose schema:

• NestJS Mongoose: test/nestjs-mongoose.e2e-spec.ts
• Plain Mongoose: test/mongoose.e2e-spec.ts

Set up the project by running npm install and then npm run test:e2e to run the tests.

Note: This repository uses Mongo Memory Server to run the tests (and provide a throwaway database environment for running the application). I have experienced issues getting it running on NixOS in the past.

To verify that the issue doesn't just exist in the test environment, I have also replicated the issue in the application itself. Run npm run start:dev to start the dev server, and then fetch http://localhost:4200 to see the following (invalid) response:

{
  "_id": "6688ab3f9d5e834ea10f9d37",
  "name": "Abstergo tergum distinctio convoco amet.",
  "author": "6688ab3f9d5e834ea10f9d25",
  "sections": [
    {
      "type": "text",
      "content": "Curvo argentum arbustum. Tersus magnam anser conduco stabilis vix ago aedificium vindico cuppedia. Utor ubi calcar tenus absum vinitor solvo canto."
    },
    {
      "type": "embed",
      "embeds": [],
      "embedType": "Author"
    },
    {
      "type": "image",
      "uri": "https://picsum.photos/seed/yAvxSQIGk/640/480",
      "credits": "Stips velum vulariter. Desidero tabgo delibero aedificium conculco velut caritas. Defaeco clam valens verumtamen velociter velociter."
    },
    {
      "type": "embed",
      "embeds": [],
      "embedType": "Spotlight"
    }
  ],
  "__v": 0
}

Workaround

Fortunately there is a workaround, demonstrated in the workaround branch where we use the NestJS Mongoose schema to define the discriminator, and then use a plain Mongoose schema to define the embedded discriminator:

 ArticleSectionSchema.discriminator(
   ArticleSectionType.Embed,
-  ArticleEmbedSectionSchema,
+  new mongoose.Schema({
+    embeds: {
+      type: [
+        {
+          type: mongoose.Schema.Types.ObjectId,
+          ref() {
+            return this.embedType;
+          },
+        },
+      ],
+      required: true,
+    },
+    embedType: {
+      type: String,
+      required: true,
+      enum: ['Author', 'Article', 'Post', 'Comment', 'Spotlight'],
+    },
+  }),
 );

The expected output for the application is:

{
  "_id": "6688a3cb4e3fa6c920bc88fc",
  "name": "Textor utilis baiulus tergeo.",
  "author": "6688a3cb4e3fa6c920bc88e8",
  "sections": [
    {
      "type": "text",
      "content": "Administratio pecco suasoria. Creptio vulgaris caste denuo vel advoco utique aegre vomer. Cura xiphias vir suffragium sint.",
      "_id": "6688a3cb4e3fa6c920bc88fd"
    },
    {
      "type": "embed",
      "embeds": [
        {
          "_id": "6688a3cb4e3fa6c920bc88e6",
          "name": "Luke Koch-Aufderhar",
          "description": "aid junkie  🧙🏿",
          "__v": 0
        },
        {
          "_id": "6688a3cb4e3fa6c920bc88e7",
          "name": "Jeffery Braun Sr.",
          "description": "teacher junkie, scientist",
          "__v": 0
        }
      ],
      "embedType": "Author",
      "_id": "6688a3cb4e3fa6c920bc88fe"
    },
    {
      "type": "image",
      "uri": "https://picsum.photos/seed/LGbnTd/640/480",
      "credits": "Utor infit capio autem caveo sufficio. Pecto asporto circumvenio decens arcesso qui sursum. Crustulum cedo aperio ubi alius.",
      "_id": "6688a3cb4e3fa6c920bc88ff"
    },
    {
      "type": "embed",
      "embeds": [
        {
          "_id": "6688a3cb4e3fa6c920bc88f8",
          "docs": [
            "6688a3cb4e3fa6c920bc88ec",
            "6688a3cb4e3fa6c920bc88ee"
          ],
          "docsModel": "Article",
          "__v": 0
        },
        {
          "_id": "6688a3cb4e3fa6c920bc88f9",
          "docs": [
            "6688a3cb4e3fa6c920bc88f2",
            "6688a3cb4e3fa6c920bc88f3",
            "6688a3cb4e3fa6c920bc88f4"
          ],
          "docsModel": "Post",
          "__v": 0
        }
      ],
      "embedType": "Spotlight",
      "_id": "6688a3cb4e3fa6c920bc8900"
    }
  ],
  "__v": 0
}

See how the embeds are populated instead?