feat(index): added createInitialConnection option to Mongoose constru…

…ctor

closes #12965

lib/index.js

@@ -71,8 +71,11 @@ function Mongoose(options) {
     autoIndex: true,
     autoCreate: true
   }, options);
-  const conn = this.createConnection(); // default connection
-  conn.models = this.models;
+  const createInitialConnection = utils.getOption('createInitialConnection', this.options) ?? true;
+  if (createInitialConnection) {
+    const conn = this.createConnection(); // default connection
+    conn.models = this.models;
+  }
 
   if (this.options.pluralization) {
     this._pluralize = legacyPluralize;

test/connection.test.js

@@ -1545,4 +1545,11 @@ describe('connections:', function() {
     const res = await m.connection.db.listCollections().toArray();
     assert.ok(!res.map(c => c.name).includes('gh12940_Conn'));
   });
+
+  it('should not create default connection with createInitialConnection = false (gh-12965)', function() {
+    const m = new mongoose.Mongoose({
+      createInitialConnection: false
+    });
+    assert.deepEqual(m.connections.length, 0);
+  });
 });

types/mongooseoptions.d.ts

@@ -63,6 +63,13 @@ declare module 'mongoose' {
      */
     cloneSchemas?: boolean;
 
+    /**
+     * Set to `false` to disable the creation of the initial default connection.
+     *
+     * @default true
+     */
+    createInitialConnection?: boolean;
+
     /**
      * If `true`, prints the operations mongoose sends to MongoDB to the console.
      * If a writable stream is passed, it will log to that stream, without colorization.