feat(connection): add Connection.prototype.removeDb() for removing a related connection

lib/connection.js

@@ -1418,6 +1418,29 @@ Connection.prototype.syncIndexes = async function syncIndexes(options = {}) {
  * @api public
  */
 
+/**
+ * Removes the database connection with the given name created with with `useDb()`.
+ *
+ * Throws an error if the database connection was not found.
+ *
+ * #### Example:
+ *
+ *     // Connect to `initialdb` first
+ *     const conn = await mongoose.createConnection('mongodb://127.0.0.1:27017/initialdb').asPromise();
+ *
+ *     // Creates an un-cached connection to `mydb`
+ *     const db = conn.useDb('mydb');
+ *
+ *     // Closes `db`, and removes `db` from `conn.relatedDbs` and `conn.otherDbs`
+ *     await conn.removeDb('mydb');
+ *
+ * @method removeDb
+ * @memberOf Connection
+ * @param {String} name The database name
+ * @return {Connection} this
+ * @api public
+ */
+
 /*!
  * Module exports.
  */

lib/drivers/node-mongodb-native/connection.js

@@ -126,6 +126,44 @@ NativeConnection.prototype.useDb = function(name, options) {
   return newConn;
 };
 
+/**
+ * Removes the database connection with the given name created with with `useDb()`.
+ *
+ * Throws an error if the database connection was not found.
+ *
+ * #### Example:
+ *
+ *     // Connect to `initialdb` first
+ *     const conn = await mongoose.createConnection('mongodb://127.0.0.1:27017/initialdb').asPromise();
+ *
+ *     // Creates an un-cached connection to `mydb`
+ *     const db = conn.useDb('mydb');
+ *
+ *     // Closes `db`, and removes `db` from `conn.relatedDbs` and `conn.otherDbs`
+ *     await conn.removeDb('mydb');
+ *
+ * @method removeDb
+ * @memberOf Connection
+ * @param {String} name The database name
+ * @return {Connection} this
+ */
+
+NativeConnection.prototype.removeDb = function removeDb(name) {
+  const dbs = this.otherDbs.filter(db => db.name === name);
+  if (!dbs.length) {
+    throw new MongooseError(`No connections to database "${name}" found`);
+  }
+
+  for (const db of dbs) {
+    db._closeCalled = true;
+    db._destroyCalled = true;
+    db._readyState = STATES.disconnected;
+    db.$wasForceClosed = true;
+  }
+  delete this.relatedDbs[name];
+  this.otherDbs = this.otherDbs.filter(db => db.name !== name);
+};
+
 /**
  * Closes the connection
  *

test/connection.test.js

@@ -6,6 +6,7 @@
 
 const start = require('./common');
 
+const STATES = require('../lib/connectionstate');
 const Q = require('q');
 const assert = require('assert');
 const mongodb = require('mongodb');
@@ -746,6 +747,35 @@ describe('connections:', function() {
       assert.strictEqual(db2, db3);
       return db.close();
     });
+
+    it('supports removing db (gh-11821)', async function() {
+      const db = await mongoose.createConnection(start.uri).asPromise();
+
+      const schema = mongoose.Schema({ name: String }, { autoCreate: false, autoIndex: false });
+      const Test = db.model('Test', schema);
+      await Test.deleteMany({});
+      await Test.create({ name: 'gh-11821' });
+
+      const db2 = db.useDb(start.databases[1]);
+      const Test2 = db2.model('Test', schema);
+
+      await Test2.deleteMany({});
+      let doc = await Test2.findOne();
+      assert.equal(doc, null);
+
+      db.removeDb(start.databases[1]);
+      assert.equal(db2.readyState, STATES.disconnected);
+      assert.equal(db.readyState, STATES.connected);
+      await assert.rejects(
+        () => Test2.findOne(),
+        /Connection was force closed/
+      );
+
+      doc = await Test.findOne();
+      assert.equal(doc.name, 'gh-11821');
+
+      await db.close();
+    });
   });
 
   describe('shouldAuthenticate()', function() {