NiFi, Jolt's operation "substring" doesn't work - json

Question

I have some datetime marks, and what I pretend is to group it in the quarter of hour just before it.
I have, e.g., this data:
[
{
"id": "123",
"dateTime": "2020-07-08T08:49:50+02:00",
"value": "1"
},
{
"id": "123",
"dateTime": "2020-07-08T13:14:57+02:00",
"value": "1"
},
{
"id": "123",
"dateTime": "2020-07-08T13:15:15+02:00",
"value": "1"
},
{
"id": "123",
"dateTime": "2020-07-08T13:36:39+02:00",
"value": "1"
}
]
After some JOLT Transformations, I have this data:
[ {
"id" : "123",
"dateHour" : "2020-07-08T08",
"minutes" : "45",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "0",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "15",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "30",
"value" : "1"
} ]
here, I have a problem. With the webpage http://jolt-demo.appspot.com/, I have managed to convert that "0" in "00" with the following JOLT code
[
{ "operation": "modify-overwrite-beta",
"spec": {
"*": {
"minutes": "=concat('0',#(0))"
}
}
},
{ "operation": "modify-overwrite-beta",
"spec": {
"*": {
"minutes": "=substring(#(1,minutes),1,3)"
}
}
}
]
Expected output (and achived with the webpage):
[ {
"id" : "123",
"dateHour" : "2020-07-08T08",
"minutes" : "45",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "00",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "15",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "30",
"value" : "1"
} ]
Real output in NiFi:
[ {
"id" : "123",
"dateHour" : "2020-07-08T08",
"minutes" : "045",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "00",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "015",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "030",
"value" : "1"
} ]
For some reason, "=substring()" function doesn't work as I expected in NiFi. Does anyone have any knack to take the last 2 items of the string?

Answer 1

You can convert to number and leftPad it. See if it helps
[
{
"operation": "modify-overwrite-beta",
"spec": {
"*": {
"minutes": ["=toInteger", 0]
}
}
},
{
"operation": "modify-overwrite-beta",
"spec": {
"*": {
"minutes": "=toString"
}
}
},
{
"operation": "modify-overwrite-beta",
"spec": {
"*": {
"minutes": "=leftPad(#(1,minutes),2,'0')"
}
}
}
]
Input:
[
{
"id": "123",
"dateHour": "2020-07-08T08",
"minutes": "045",
"value": "1"
},
{
"id": "123",
"dateHour": "2020-07-08T13",
"minutes": "00",
"value": "1"
},
{
"id": "123",
"dateHour": "2020-07-08T13",
"minutes": "015",
"value": "1"
},
{
"id": "123",
"dateHour": "2020-07-08T13",
"minutes": "030",
"value": "1"
}
]
output:
[ {
"id" : "123",
"dateHour" : "2020-07-08T08",
"minutes" : "45",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "00",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "15",
"value" : "1"
}, {
"id" : "123",
"dateHour" : "2020-07-08T13",
"minutes" : "30",
"value" : "1"
} ]