code: function getDatabase() {
      var mongoAdapter = this;
  
      expect(arguments).to.have.length(
        0,
        'Invalid arguments length when getting a database in a MongoAdapter ' +
        '(it has to be passed no arguments)'
      );
  
      return new Promise(function (resolve, reject) {
        if (_databaseIsLocked || !_database) {
          mongoAdapter
            .openConnection()
            .then(function () {
              resolve(_database);
            })
            .catch(reject);
        } else {
          resolve(_database);
        }
      });
    }
docs: Gets the MongoClient Db object to be use to perform the operations.
  @name module:back4app-entity-mongodb.MongoAdapter#getDatabase
  @function
  @returns {Promise.<Db|Error>} Promise that returns the MongoClient Db
  object if succeed and the Error if failed.
  @example
  mongoAdapter.getDatabase()
  .then(function (database) {
  database.createCollection('myCollection');
  })
  .catch(function (error) {
  console.log(error);
  });