feat(connection): add listCollections() helper to connections

lib/connection.js

@@ -605,6 +605,30 @@ Connection.prototype.dropCollection = async function dropCollection(collection)
   return this.db.dropCollection(collection);
 };
 
+/**
+ * Helper for MongoDB Node driver's `listCollections()`.
+ * Returns an array of collection objects.
+ *
+ * @method listCollections
+ * @return {Promise<Collection[]>}
+ * @api public
+ */
+
+Connection.prototype.listCollections = async function listCollections() {
+  if (arguments.length >= 2 && typeof arguments[1] === 'function') {
+    throw new MongooseError('Connection.prototype.dropCollection() no longer accepts a callback');
+  }
+
+  if ((this.readyState === STATES.connecting || this.readyState === STATES.disconnected) && this._shouldBufferCommands()) {
+    await new Promise(resolve => {
+      this._queue.push({ fn: resolve });
+    });
+  }
+
+  const cursor = this.db.listCollections();
+  return await cursor.toArray();
+};
+
 /**
  * Helper for `dropDatabase()`. Deletes the given database, including all
  * collections, documents, and indexes.

test/connection.test.js

@@ -195,6 +195,14 @@ describe('connections:', function() {
       const newCollectionsNames = collectionsAfterCreation.map(function(c) { return c.name; });
       assert.ok(newCollectionsNames.indexOf('gh5712') !== -1);
     });
+
+    it('listCollections()', async function() {
+      await conn.dropDatabase();
+      await conn.createCollection('test1176');
+
+      const collections = await conn.listCollections();
+      assert.deepStrictEqual(collections.map(coll => coll.name), ['test1176']);
+    });
   });
 
   it('should allow closing a closed connection', async function() {

types/connection.d.ts

@@ -121,6 +121,12 @@ declare module 'mongoose' {
      */
     readonly id: number;
 
+    /**
+     * Helper for MongoDB Node driver's `listCollections()`.
+     * Returns an array of collection names.
+     */
+    listCollections(collection: string): Promise<Pick<mongodb.CollectionInfo, 'name' | 'type'>[]>;
+
     /**
      * A [POJO](https://masteringjs.io/tutorials/fundamentals/pojo) containing
      * a map from model names to models. Contains all models that have been