如何按照名字(first_name)排序这个JSON对象?
{
1 :{user_id:1, first_name:"first_name1", last_name:"lastname1", email:"user1@test.com"},
7 :{user_id:7, first_name:"user2", last_name:"test2", email:""},
72 :{user_id:72, first_name:"testing343", last_name:"", email:""},
246:{user_id:246, first_name:"aaa", last_name:"ssss", email:""}
}