add query modifier function support.

README.md

@@ -50,6 +50,8 @@ __Options:__
 - `overwrite` (*optional*, default: `true`) - Overwrite the document when update, making mongoose detect is new document and trigger default value for unspecified properties in mongoose schema.
 - `discriminators` (*optional*) - A list of mongoose models that inherit from `Model`.
 - `useEstimatedDocumentCount` (*optional*, default: `false`) - Use `estimatedDocumentCount` instead (usually not necessary)
+- `queryModifier` (*optional*) - A function that takes in the raw mongoose Query object and params, which modifies all find and get requests unless overridden. (see Query Modifiers below)
+- `queryModifierKey` (*optional*, default: `'queryModifier'`) - The key to use to get the override query modifier function from the params. (see Query Modifiers below)
 
 > **Important:** To avoid odd error handling behaviour, always set `mongoose.Promise = global.Promise`. If not available already, Feathers comes with a polyfill for native Promises.
 
@@ -346,6 +348,48 @@ let moduleExports = {
 module.exports = moduleExports;
 ```
 
+## Query Modifiers
+
+Sometimes it's important to use an unusual Mongoose Query method, like [specifying whether to read from a primary or secondary node,](https://mongoosejs.com/docs/api.html#query_Query-read) but maybe only for certain requests.
+
+You can access the internal Mongoose Query object used for a find/get request by specifying the queryModifier function. It is also possible to override that global function by specifying the function in a requests params.
+
+```js
+// Specify a global query modifier when creating the service
+app.use('/messages', service({
+  Model,
+  queryModifier: (query, params) => {
+    query.read('secondaryPreferred');
+  }
+}));
+
+app.service('messages').find({
+  query: { ... },
+}).then((result) => {
+  console.log('Result from secondary:', result)
+});
+
+// Override the modifier on a per-request basis
+app.service('messages').find({
+  query: { ... },
+  queryModifier: (query, params) => {
+    query.read('primaryPreferred');
+  }
+}).then((result) => {
+  console.log('Result from primary:', result)
+});
+
+// Disable the global modifier on a per-request basis
+app.service('messages').find({
+  query: { ... },
+  queryModifier: false
+}).then((result) => {
+  console.log('Result from default option:', result)
+});
+```
+
+> **Note:** Due to replication lag, a secondary node can have "stale" data. You should ensure that this "staleness" will not be an issue for your application before reading from the secondary set.
+
 ## Contributing
 
 This module is community maintained and open for pull requests. Features and bug fixes should contain

lib/service.js

@@ -19,7 +19,8 @@ class Service extends AdapterService {
         $populate (value) {
           return value;
         }
-      }, options.filters)
+      }, options.filters),
+      queryModifierKey: 'queryModifier'
     }, options, {
       whitelist: whitelist.concat('$and')
     }));
@@ -40,6 +41,18 @@ class Service extends AdapterService {
     return this.options.Model;
   }
 
+  _getQueryModifier (params) {
+    if (typeof params[this.options.queryModifierKey] === 'function') {
+      return params[this.options.queryModifierKey];
+    }
+    if (params[this.options.queryModifierKey] !== false) {
+      if (typeof this.options.queryModifier === 'function') {
+        return this.options.queryModifier;
+      }
+    }
+    return () => {};
+  }
+
   _getOrFind (id, params = {}) {
     if (id === null) {
       return this._find(params);
@@ -88,6 +101,8 @@ class Service extends AdapterService {
       q.populate(filters.$populate);
     }
 
+    this._getQueryModifier(params)(q, params);
+
     let executeQuery = total => q.session(params.mongoose && params.mongoose.session).exec().then(data => {
       return {
         total,
@@ -141,6 +156,8 @@ class Service extends AdapterService {
       modelQuery.select(filters.$select);
     }
 
+    this._getQueryModifier(params)(modelQuery, params);
+
     return modelQuery.session(params.mongoose && params.mongoose.session)
       .lean(this.lean).exec().then(data => {
         if (!data) {

test/index.test.js

@@ -115,6 +115,13 @@ const app = feathers()
     multi: true,
     whitelist: ['$populate']
   }))
+  .use('/pets3', adapter({
+    Model: Pet,
+    multi: true,
+    queryModifier: (query) => {
+      query.where('type', 'cat');
+    }
+  }))
   .use('/posts', adapter({
     Model: Post,
     discriminators: [TextPost],
@@ -125,6 +132,7 @@ const people = app.service('people');
 const pets = app.service('pets');
 const leanPeople = app.service('people2');
 const leanPets = app.service('pets2');
+const QMPets = app.service('pets3');
 const posts = app.service('posts');
 
 describe('Feathers Mongoose Service', () => {
@@ -631,6 +639,92 @@ describe('Feathers Mongoose Service', () => {
     });
   });
 
+  describe('Query Modifiers', () => {
+    beforeEach(async () => {
+      const rufus = await QMPets.create({ type: 'dog', name: 'Rufus' });
+      const margeaux = await QMPets.create({ type: 'cat', name: 'Margeaux' });
+      const bob = await QMPets.create({ type: 'cat', name: 'Bob' });
+
+      _petIds.Rufus = rufus._id;
+      _petIds.Margeaux = margeaux._id;
+      _petIds.Bob = bob._id;
+    });
+
+    afterEach(async () => {
+      await QMPets.remove(null, { query: {} });
+    });
+
+    it('can apply a global query modifier with find', async () => {
+      const params = {
+        query: {}
+      };
+
+      const data = await QMPets.find(params);
+
+      expect(data.length).to.equal(2);
+      expect(data[0].type).to.equal('cat');
+      expect(data[1].type).to.equal('cat');
+    });
+
+    it('can apply a global query modifier with get', async () => {
+      const margeaux = await QMPets.get(_petIds.Margeaux);
+
+      expect(margeaux.name).to.equal('Margeaux');
+
+      try {
+        await QMPets.get(_petIds.Rufus);
+        throw new Error('Should never get here');
+      } catch (error) {
+        expect(error.name).to.equal('NotFound');
+      }
+    });
+
+    it('can apply a local query modifier with find', async () => {
+      const params = {
+        query: {},
+        queryModifier: (query) => {
+          query.where('type', 'dog');
+        }
+      };
+
+      const data = await QMPets.find(params);
+
+      expect(data.length).to.equal(1);
+      expect(data[0].type).to.equal('dog');
+    });
+
+    it('can apply a local query modifier with get', async () => {
+      const params = {
+        query: {},
+        queryModifier: (query) => {
+          query.where('type', 'dog');
+        }
+      };
+
+      const result = await QMPets.get(_petIds.Rufus, params);
+
+      expect(result.name).to.equal('Rufus');
+
+      try {
+        await QMPets.get(_petIds.Margeaux, params);
+        throw new Error('Should never get here');
+      } catch (error) {
+        expect(error.name).to.equal('NotFound');
+      }
+    });
+
+    it('can disable the global query modifier', async () => {
+      const params = {
+        query: {},
+        queryModifier: false
+      };
+
+      const data = await QMPets.find(params);
+
+      expect(data.length).to.equal(3);
+    });
+  });
+
   testSuite(app, errors, 'peeps', '_id');
   testSuite(app, errors, 'peeps-customid', 'customid');
 });

types/index.d.ts

@@ -1,7 +1,7 @@
 // TypeScript Version: 4.0
 import { Params, Paginated, Id, NullableId, Hook } from '@feathersjs/feathers';
 import { AdapterService, ServiceOptions, InternalServiceMethods } from '@feathersjs/adapter-commons';
-import { Model, Document } from 'mongoose';
+import { Model, Document, Query } from 'mongoose';
 
 export namespace hooks {
   function toObject(options?: any, dataField?: string): Hook;
@@ -18,6 +18,8 @@ export interface MongooseServiceOptions<T extends Document = any> extends Servic
   lean: boolean;
   overwrite: boolean;
   useEstimatedDocumentCount: boolean;
+  queryModifier?: (query: Query, params: Params) => void;
+  queryModifierKey?: string;
 }
 
 export class Service<T = any> extends AdapterService<T> implements InternalServiceMethods<T> {