jsonjsonschemajson-schema-validator

Implementing a constraint inside $def using the field value from a higher level schema


Below is a simplified / sanitized view of my actual schema. Is it possible to implement a constraint on fieldD (lets say a constraint on array size) using the value of fieldA?


{
    "$schema": "https://json-schema.org/draft/2020-12/schema",
    "type": "object",
    "properties": {
        "fieldA": {
            "type": "boolean"
        },
        "fieldB": {
            "type": "object",
            "$ref": "#/$defs/fieldB"
        }
    },
    "$defs": {
        "fieldB": {
            "type": "object",
            "properties": {
                "fieldC": {
                    "type": "string"
                },
                "fieldD": {
                    "$ref": "#/$defs/fieldD"
                }
            }
        },
        "fieldD": {
            "type": "array"
        }
    }
}

Solution

  • You can use if, then syntax to check conditions on fieldA and apply constraints on fieldD

    {
        "$schema": "https://json-schema.org/draft/2020-12/schema",
        "type": "object",
        "properties": {
            "fieldA": {
                "type": "boolean"
            },
            "fieldB": {
                "type": "object",
                "$ref": "#/$defs/fieldB"
            }
        },
        "$defs": {
            "fieldB": {
                "type": "object",
                "properties": {
                    "fieldC": {
                        "type": "string"
                    },
                    "fieldD": {
                        "$ref": "#/$defs/fieldD"
                    }
                }
            },
            "fieldD": {
                "type": "array"
            }
        },
        "if": {
            "required": ["fieldA"],
            "properties": {
                "fieldA": {
                    "const": true
                }
            }
        },
        "then": {
            "properties": {
                "fieldB": {
                    "properties": {
                        "fieldD": {
                            "minItems": 1
                        }
                    }
                }
            }
        },
        "else": {
            "properties": {
                "fieldB": {
                    "properties": {
                        "fieldD": {
                           <some other constraint or omit `else` completely for a default behavior>                    }
                    }
                }
            }
        }
    }