mysql - Atomic in MongoDB with transfer money -

i'm new mongodb make simple application abount account in bank.an account can transfer money others design account collection that

account {          name:a          age: 24          money: 100 }  account {          name:b          age: 22          money: 300 } 

assuming user transfer 100$ user b , there 2 operations : 1) decrease 100$ in user // update document 2) increase 100$ user b // update document b said atomic applied single document no mutiple document.

i have alter desgign

bank {       name:       address:       account[        {          name:a          age: 22          money: ss }, {          name:b          age: 23          money: s1s } ] }  

i have question :

• if use later way, how can write transaction query (can use findandmodify() function?) ?
• does mongodb support transaction operations mysql (innodb)?
• some pepple tell me use mysql project best way, , use mongodb save transaction information.(use collection named transaction_money save them), if use both mongodb , mysql (innodb) how can make operations below atomic (fail or success whole):

> 1) -100$ user  > 2) +100$ user b  > 3) save transaction 

information like

transaction {    sender:    receiver: b    money : 100    date: 05/04/2013 } 

thank much.

i not sure looking for:

db.bank.update({name : "name"},{ "$inc" : {'account.0.money' : -100, 'account.1.money' : 100}}) 

• update() operation satisfies aci properties of ( acid ). durability ( d ) depends on mongo , application configuration while making query.
• you can prefer use findandmodify() won't yield lock on page fault
• mongodb provides transactions within document

i can't understand, if application requirement simple, why trying use mongodb. no doubt data-store, guess mysql satisfy requirements.

just fyi : there doc problem trying solve. http://docs.mongodb.org/manual/tutorial/perform-two-phase-commits/ won't recommend use because single query ( transferring money) has been turned sequence of queries.

hope helped