feat: useConnection(connection) function

lib/model.js

@@ -146,6 +146,21 @@ Model.prototype.$isMongooseModelPrototype = true;
 
 Model.prototype.db;
 
+/**
+ * @api public
+ */
+
+Model.useConnection = function useConnection(connection) {
+  if (!connection) {
+    throw new Error('Please provide a connection.');
+  }
+  if (this.db) {
+    delete this.db.models[this.modelName];
+  }
+  this.db = connection;
+  connection.models[this.modelName] = this;
+};
+
 /**
  * The collection instance this model uses.
  * A Mongoose collection is a thin wrapper around a [MongoDB Node.js driver collection]([MongoDB Node.js driver collection](https://mongodb.github.io/node-mongodb-native/Next/classes/Collection.html)).

test/model.test.js

@@ -7575,6 +7575,16 @@ describe('Model', function() {
 
     assert.strictEqual(doc.__v, 0);
   });
+  it('updates the model\'s db property to point to the provided connection instance and vice versa', async function() {
+    const schema = new mongoose.Schema({
+      name: String
+    });
+    const Model = db.model('Test', schema);
+    const connection = start();
+    Model.useConnection(connection);
+    assert.equal(db.models[Model.modelName], undefined);
+    assert(connection.models[Model.modelName]);
+  });
 });