If you have defined the Member class with auto-incremented Id, there is no additional query you have to write, because the Id property is filled automatically after the saveChanges().
To define a auto-incremented Id to your class, check if you have written this:
$data.Entity.extend("Member", {
Id: { type: "int", key: true, computed: true },
...
});
var member = new Member();
member.Name = "a";
DB.Members.add(member);
DB.Members.saveChanges(function(){alert(member.Id);});
If the Id is set manually, your query is valid only in a scenario where the records are inserted manually by a single user of the app. We have to work out a solution together if you sync data from an online datastore.
Does it work?