feat(shell-api): add Mongo.getCollection() MONGOSH-620

packages/i18n/src/locales/en_US.ts

@@ -1656,6 +1656,11 @@ const translations: Catalog = {
               link: 'https://docs.mongodb.com/manual/reference/method/Mongo.startSession/',
               description: 'Starts a session for the connection.'
             },
+            getCollection: {
+              link: 'https://docs.mongodb.com/manual/reference/method/Mongo.getCollection',
+              description: 'Returns the specified Collection of the Mongo object.',
+              example: 'const collection = db.getMongo().getCollection("databaseName.collectionName")'
+            },
             getDB: {
               link: 'https://docs.mongodb.com/manual/reference/method/Mongo.getDB',
               description: 'Returns the specified Database of the Mongo object.'

packages/shell-api/src/mongo.spec.ts

@@ -609,6 +609,39 @@ describe('Mongo', () => {
         expect.fail('Failed to throw');
       });
     });
+    describe('getCollection', () => {
+      it('returns a collection for the database', async() => {
+        const coll = mongo.getCollection('db1.coll');
+        expect(coll).to.be.instanceOf(Collection);
+        expect(coll._name).to.equal('coll');
+        expect(coll._database._name).to.equal('db1');
+      });
+
+      it('returns a collection for the database with multiple .', async() => {
+        const coll = mongo.getCollection('db1.coll.subcoll');
+        expect(coll).to.be.instanceOf(Collection);
+        expect(coll._name).to.equal('coll.subcoll');
+        expect(coll._database._name).to.equal('db1');
+      });
+
+      it('throws if name is not a valid connection string', () => {
+        expect(() => {
+          mongo.getCollection('db');
+        }).to.throw('Collection must be of the format <db>.<collection>');
+      });
+
+      it('throws if name is empty', () => {
+        expect(() => {
+          mongo.getCollection('');
+        }).to.throw('Collection must be of the format <db>.<collection>');
+      });
+
+      it('throws if name starts with dot', () => {
+        expect(() => {
+          mongo.getCollection('.coll');
+        }).to.throw('Collection must be of the format <db>.<collection>');
+      });
+    });
   });
 
   describe('integration', () => {

packages/shell-api/src/mongo.ts

@@ -36,6 +36,7 @@ import {
   ServerApi,
   ServerApiVersionId
 } from '@mongosh/service-provider-core';
+import type Collection from './collection';
 import Database from './database';
 import ShellInternalState from './shell-internal-state';
 import { CommandResult } from './result';
@@ -194,6 +195,16 @@ export default class Mongo extends ShellApiClass {
     return this._getDb(db);
   }
 
+  @returnType('Collection')
+  getCollection(name: string): Collection {
+    assertArgsDefinedType([name], ['string']);
+    const { db, coll } = name.match(/^(?<db>[^.]+)\.(?<coll>.+)$/)?.groups ?? {};
+    if (!db || !coll) {
+      throw new MongoshInvalidInputError('Collection must be of the format <db>.<collection>', CommonErrors.InvalidArgument);
+    }
+    return this._getDb(db).getCollection(coll);
+  }
+
   use(db: string): string {
     assertArgsDefinedType([db], ['string'], 'Mongo.use');
     this._internalState.messageBus.emit('mongosh:use', { db });