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');
 
@@ -73,6 +74,7 @@ function Mongoose(options) {
   const createInitialConnection = utils.getOption('createInitialConnection', this.options) ?? true;
   if (createInitialConnection && this.__driver != null) {
     const conn = this.createConnection(); // default connection
+    conn[defaultConnectionSymbol] = true;
     conn.models = this.models;
   }
 
@@ -292,6 +294,16 @@ Mongoose.prototype.set = function(key, value) {
       } else if (!optionValue && _mongoose.transactionAsyncLocalStorage) {
         delete _mongoose.transactionAsyncLocalStorage;
       }
+    } else if (optionKey === 'createInitialConnection') {
+      if (optionValue && !_mongoose.connection) {
+        const conn = this.createConnection(); // default connection
+        conn[defaultConnectionSymbol] = true;
+        conn.models = this.models;
+      } 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();
+        }
+      }
     }
   }
 

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 +1180,14 @@ describe('mongoose module:', function() {
       }
     });
   });
+
+  it('setting createInitialConnection after creation deletes existing connection (gh-8302)', async function() {
+    const m = new mongoose.Mongoose();
+    assert.ok(m.connection);
+    m.set('createInitialConnection', false);
+    assert.strictEqual(m.connection, undefined);
+
+    const conn = m.createConnection();
+    assert.equal(conn, m.connection);
+  });
 });