How to model complex schema without much repetition using JsonSchema? - json

Question

I am trying to model documents (such as passport) and their attributes (first name, birth date, etc) and describe them using json schema.
I want to define many types of documents in runtime, every document as a separate schema.
Some attributes may be referenced from multiple documents, such as firstName in passport and in driver's license, so it is
probably wise to create a separate attribute definition schema for this.
Lets say, I have a passport, its model looks like following:
{
"owner": "<string>",
"type" : "<string>",
"salt" : <number>,
"attributes": {
"number" : {"value": "<string>", "salt": <number>}
"lastName" : {"value": "<string>", "salt": <number>},
"firstName" : {"value": "<string>", "salt": <number>},
"birthDate" : {"value": "<date>", "salt": <number>},
"nationality": {"value": "<string>", "salt": <number>},
}
}
Every attribute has "value" and "salt", but "value" is different for every key (attribute name).
My question is, how will schema for this type of JSON document look?
UPD: every attribute has value and salt. Salt is exactly equal for all attributes, but value is different. If I manually specify that every attribute has salt and value, then I will end up with huge schema duplication. Is it possible to avoid it?

Answer 1

There are plenty of things you can do to reduce the duplication in your schema. One way is to use the definitions keyword. Another option is to use patternProperties to validate common constraints across multiple properties.
{
"type": "object",
"properties": {
"owner": { "type": "string" },
"type": { "type": "string" },
"salt": { "$ref": "#/definitions/salt" },
"attributes": {
"type": "object",
"patternProperties": {
".*": {
"type": "object",
"properties": {
"salt": { "$ref": "#/definitions/salt" }
},
"required": ["value", "salt"]
}
},
"properties": {
"number": { "$ref": "#/definitions/string-value" },
"lastName": { "$ref": "#/definitions/string-value" },
"firstName": { "$ref": "#/definitions/string-value" },
"birthDate": { "$ref": "#/definitions/date-value" },
"nationality": { "$ref": "#/definitions/string-value" }
}
}
},
"definitions": {
"salt": { "const": 1234 },
"string-value": {
"properties": {
"value": { "type": "string" }
}
},
"date-value": {
"properties": {
"value": { "type": "string", "format": "date" }
}
}
}
}

Answer 2

With draft-7 of JSON Schema (current at time of writing), assuming you'll want to be using references to another file which contains your property definitions, you may want to do something like the following.
{
"$schema": "http://json-schema.org/draft-07/schema#",
"properties": {
"number": {
"properties": {
"value": {...}, # Whatever you define as your schema for number/value.
"salt": {
"$ref": "externalRef/definitions/salt"
}
}
}
}
}