android - Find object A and number of objects B has pointer with object A in a query -

i have big question , need help. it's parse sdk.

i have 2 class named , b. b has column named author pointer a.

my question: in query find object a, want number of b object has pointer a. if cannot in query, can suggest me solution task minimum request parse? thanks.

parsequery<parseobject> query = parsequery.getquery("b"); query.whereequalto("pointertoa", objecta ); query.countinbackground(new countcallback() {  public void done(int count, parseexception e) {{     if (e == null) {         // "use count     } else {         // went wrong...     } } });