{ $pull :

{ field : _value }

} will removes all occurrences of value from field, if field is an array.
In my project, I need { $pull :

{ field : _value }

} removes the first occurrences of value from field.
For example:
document:

{ "_id":"123", "boys":[ {"name":"jhon"}

,

{"name":"jhon"}

,

{"name":"gavin"}

]
}
As you see, the array "boys" has three elements, and the first is same
to the second. If I do {$pull:{"name":"jhon"}}, then the first and second element will be removed.
Actually, I just want to remove the first element(left the second element and the third element).