How to query by key?

Hi I could not find the answer to this problem:

Given the following structure, how do I get all the "objects" those **keys** start with e.g 'block8'?
```
{
"prod_data": {
"block2.row2": {
"status": "yes",
"date": "2016-05-09",
"name": "Karin",
"time": "06:57:28"
},
"block8.row4": {
"status": "yes",
"date": "2016-05-18",
"name": "Isolde",
"time": "11:22:02"
},
"block3.row1": {
"status": "yes",
"date": "2016-05-13",
"name": "Isolde",
"time": "13:11:59"
},
"block8.row2": {
"status": "yes",
"date": "2016-05-18",
"name": "Isolde",
"time": "11:22:02"
}
}
}
```