Why does JSON Schema maximum not work in allOf? - json

Question

Given the following JSON schema:
{
"$schema": "https://json-schema.org/draft/2019-09/schema",
"properties": {
"pageA": {
"properties": {
"a": { "type": "number" },
},
"allOf": [
{
"if": {
"properties": {
"a": { "maximum": 10 }
}
},
"then": {
"properties": {
"b": { "type": "number" },
"c": { "type": "string" }
}
},
"else": {
"allOf": [
{
"if": {
"properties": {
"a": { "maximum": 20 }
}
},
"then": {
"properties": {
"e": { "type": "number" },
"f": { "type": "string" }
}
},
"else": {
"allOf": [
{
"if": {
"properties": {
"a": { "maxiumum": 30 }
}
},
"then": {
"properties": {
"i": { "type": "number" },
"j": { "type": "string" }
}
},
"else": {
"properties": {
"k": { "type": "number" },
"l": { "type": "string" }
}
}
}
]
}
}
]
}
}
]
}
}
}
I would expect:
{
"pageA": {
"a": 31,
"k": "50"
}
}
To generate "Invalid type. Expected Number but got String." but it is valid. I understand any properties nested within an allOf cannot be caught by additionalProperties, and it appears that the validation is also applying in the similar way.

Answer 1

There are two problems with your schema. The first is super simple to solve. A typo (We've all done it).
"a": { "maxiumum": 30 } Should read maximum.
Now let's take a look at the specification to see what maximum does...
The value of "maximum" MUST be a number, representing an inclusive
upper limit for a numeric instance.
If the instance is a number, then this keyword validates only if the
instance is less than or exactly equal to "maximum".
https://json-schema.org/draft/2019-09/json-schema-validation.html#rfc.section.6.2.2
Given 30 is exactly equal to 30, you triggered your then clause as opposed to your else clause.
If you want the value to be EXCLUSIVE, there's another keyword... exclusiveMaximum, which does just that.
You can see that in action here: https://jsonschema.dev/s/8Yi6e