Don't serialize fields if it exists further up the tree - jackson

Question

Lots of my domain objects have a unit field. Currently when I serialize, every object outputs the unit field:
{
"projects": [
{
"name": "project1",
"unit": "mm",
"size": {
"x": {
"value": 100,
"unit": "mm"
},
"y": {
"value": 120,
"unit": "mm"
},
"z": {
"value": 80,
"unit": "mm"
}
},
"materials": [
{
"type": "wood",
"unit": "mm",
"size": {
"x": {
"value": 100,
"unit": "mm"
},
"y": {
"value": 120,
"unit": "mm"
},
"z": {
"value": 80,
"unit": "mm"
}
}
},
...
]
},
...
]
}
I need the individual objects to have the unit property, because they are sometimes serialized on their own. e.g.
{
"length": {
"value": 100,
"unit": "mm"
}
}
But when it is nested in another object that already specifies the unit, it leads to an awful lot of duplication.
How can I get jackson to omit the unit field if there is already a unit field with the same value somewhere further up the tree?
Here are some example outputs I want to achieve using the same instances but just changing what the root object of the serialization is:
{
"projects": [
{
"name": "project1",
"unit": "mm",
"size": {
"x": {
"value": 100
},
"y": {
"value": 120
},
"z": {
"value": 80
}
},
"materials": [
{
"type": "wood",
"size": {
"x": {
"value": 100
},
"y": {
"value": 120
},
"z": {
"value": 80
}
}
},
...
]
},
...
]
}
{
"type": "wood",
"unit": "mm",
"size": {
"x": {
"value": 100
},
"y": {
"value": 120
},
"z": {
"value": 80
}
}
}
{
"value": 100,
"unit": "mm"
}

Answer 1

AFAIK you can’t add business logic like that in the parser.
You’ll have to massage the data class before the mapper.