Can a JSON schema specify required properties in object OR array? - json

Question

I am struggling to understand if it's possible to write a json schema that requires certain properties, but also allows those properties to be in different areas of the json file (e.g. a property value can be in the main top-level object OR it can be in an array - it just needs to be somewhere).
For example, I have some devices that collect multiple temperature records over the course of a few hours and send the records in batches. However, some of the devices send the software version once in the main object, while others send the software version along with each hourly temperature record (inside a "records" array).
Example 1 (swversion sent once in main object):
{
"name": "device1",
"swversion": "1.3.abc2",
"records": [
{
"time": "10am",
"temp": 2
},
{
"time": "11am",
"temp": 4
}
]
}
Example 2 (swversion sent inside "records" array):
{
"name": "device1",
"records": [
{
"time": "10am",
"temp": 2,
"swversion": "1.3.abc2"
},
{
"time": "11am",
"temp": 4,
"swversion": "1.3.abc2"
}
]
}
Using these examples, I would like to write my schema definition as follows (the first two bullets are easy, the last one is where I'm struggling):
Main object requires name property and records array
records array can contain objects where time and temp would be required
swversion is required somewhere (could be in the main object or inside records array)
Is there a feature I'm missing in json-schema that enforces required properties, yet allows the flexibility for said properties to be anywhere (e.g. within an object OR an array), as long as they are present somewhere?

Answer 1

The anyOf keyword is a boolean OR operation. At least one of the schemas must pass for the keyword to pass. The first schema requires that the "swversion" property is present at the top level. The second schema requires that the "swversion" property is required in each of the items in the "record" array.
{
... define the easy stuff here, then ...,
"anyOf": [
{ "required": ["swversion"] },
{
"properties": {
"records": {
{ "items": { "required": ["swversion"] } }
}
}
}
]
}
In this example, "swversion" could appear in both places. If you only want to ensure that it only appear in one place (top level or items), you can use oneOf instead of anyOf.

Answer 2

Is there a feature .. that allows the flexibility for said properties to be anywhere
Not directly, but it's not difficult to express this. You can define the structure of "swversion" itself in a definition that is re-used via a reference.
In pseudocode, that would be:
any of:
the main object contains a "swversion" property,
all the items under "records" contain a "swversion" property
In code:
{
"$defs": {
"swversion": {
"type": "string",
.. other constraints?
}
},
"type": "object",
"properties": {
... other property definitions ...,
"records": {
"items": {
"type": "object",
... other definitions for the mandatory portion of records ...
}
}
},
"anyOf": [
{
"$comment": "swversion is a member of the main object",
"required": [ "swversion" ],
"properties": {
"swversion": {
"$ref": "#/$defs/swversion"
}
},
{
"$comment": "swversion is a member of all the items under the records property",
"properties": {
"records": {
"items": {
"type": "object",
"required": [ "swversion" ],
"properties": {
"swversion": {
"$ref": "#/$defs/swversion"
}
}
}
}
}
}
],
}
Note that if you are using JSON Schema version draft7 or earlier, change $defs to definitions.