Remove default connection if setting createInitialConnection to false after Mongoose instance created

lib/mongoose.js

@@ -33,6 +33,7 @@ const SetOptionError = require('./error/setOptionError');
 const applyEmbeddedDiscriminators = require('./helpers/discriminator/applyEmbeddedDiscriminators');
 
 const defaultMongooseSymbol = Symbol.for('mongoose:default');
+const defaultConnectionSymbol = Symbol('mongoose:defaultConnection');
 
 require('./helpers/printJestWarning');
 
@@ -72,8 +73,7 @@ function Mongoose(options) {
   }, options);
   const createInitialConnection = utils.getOption('createInitialConnection', this.options) ?? true;
   if (createInitialConnection && this.__driver != null) {
-    const conn = this.createConnection(); // default connection
-    conn.models = this.models;
+    _createDefaultConnection(this);
   }
 
   if (this.options.pluralization) {
@@ -292,6 +292,14 @@ Mongoose.prototype.set = function(key, value) {
       } else if (!optionValue && _mongoose.transactionAsyncLocalStorage) {
         delete _mongoose.transactionAsyncLocalStorage;
       }
+    } else if (optionKey === 'createInitialConnection') {
+      if (optionValue && !_mongoose.connection) {
+        _createDefaultConnection(_mongoose);
+      } else if (optionValue === false && _mongoose.connection && _mongoose.connection[defaultConnectionSymbol]) {
+        if (_mongoose.connection.readyState === STATES.disconnected && Object.keys(_mongoose.connection.models).length === 0) {
+          _mongoose.connections.shift();
+        }
+      }
     }
   }
 
@@ -424,6 +432,9 @@ Mongoose.prototype.connect = async function connect(uri, options) {
   }
 
   const _mongoose = this instanceof Mongoose ? this : mongoose;
+  if (_mongoose.connection == null) {
+    _createDefaultConnection(_mongoose);
+  }
   const conn = _mongoose.connection;
 
   return conn.openUri(uri, options).then(() => _mongoose);
@@ -1315,6 +1326,20 @@ Mongoose.prototype.overwriteMiddlewareResult = Kareem.overwriteResult;
 
 Mongoose.prototype.omitUndefined = require('./helpers/omitUndefined');
 
+/*!
+ * Create a new default connection (`mongoose.connection`) for a Mongoose instance.
+ * No-op if there is already a default connection.
+ */
+
+function _createDefaultConnection(mongoose) {
+  if (mongoose.connection) {
+    return;
+  }
+  const conn = mongoose.createConnection(); // default connection
+  conn[defaultConnectionSymbol] = true;
+  conn.models = mongoose.models;
+}
+
 /**
  * The exports object is an instance of Mongoose.
  *

lib/validOptions.js

@@ -15,6 +15,7 @@ const VALID_OPTIONS = Object.freeze([
   'bufferCommands',
   'bufferTimeoutMS',
   'cloneSchemas',
+  'createInitialConnection',
   'debug',
   'id',
   'timestamps.createdAt.immutable',

test/index.test.js

@@ -1180,4 +1180,52 @@ describe('mongoose module:', function() {
       }
     });
   });
+
+  describe('createInitialConnection (gh-8302)', function() {
+    let m;
+
+    beforeEach(function() {
+      m = new mongoose.Mongoose();
+    });
+
+    afterEach(async function() {
+      await m.disconnect();
+    });
+
+    it('should delete existing connection when setting createInitialConnection to false', function() {
+      assert.ok(m.connection);
+      m.set('createInitialConnection', false);
+      assert.strictEqual(m.connection, undefined);
+    });
+
+    it('should create connection when createConnection is called', function() {
+      m.set('createInitialConnection', false);
+      const conn = m.createConnection();
+      assert.equal(conn, m.connection);
+    });
+
+    it('should create a new connection automatically when connect() is called if no existing default connection', async function() {
+      assert.ok(m.connection);
+      m.set('createInitialConnection', false);
+      assert.strictEqual(m.connection, undefined);
+
+      await m.connect(start.uri);
+      assert.ok(m.connection);
+    });
+
+    it('should not delete default connection if it has models', async function() {
+      assert.ok(m.connection);
+      m.model('Test', new m.Schema({ name: String }));
+      m.set('createInitialConnection', false);
+      assert.ok(m.connection);
+    });
+
+    it('should not delete default connection if it is connected', async function() {
+      assert.ok(m.connection);
+      await m.connect(start.uri);
+      m.set('createInitialConnection', false);
+      assert.ok(m.connection);
+      assert.equal(m.connection.readyState, 1);
+    });
+  });
 });