Validate object containing object for uniqueness

Hi,

I have the example like below,
```
"obj2":
{
{
"prop1": "baz", "prop2": 999
},
{
"prop1": "qux", "prop2": 555
}
}
```

i.e object containing objects, now in this i need '**_prop1_**' field to have unique values.

**_Note:_**: I know this is possible when it is array of object, but i dont think there is any solution for the same case when object containing objects.