rapidjson/doc/schema-errors.md

Schema violation reporting

(Unreleased as of 2017-09-20)

When validating an instance against a JSON Schema, it is often desirable to report not only whether the instance is valid, but also the ways in which it violates the schema.

The SchemaValidator class collects errors encountered during validation into a JSON Value. This error object can then be accessed as validator.GetError().

The structure of the error object is subject to change in future versions of RapidJSON, as there is no standard schema for violations. The details below this point are provisional only.

[TOC]

General provisions

Validation of an instance value against a schema produces an error value. The error value is always an object. An empty object {} indicates the instance is valid.

• The name of each member corresponds to the JSON Schema keyword that is violated.
• The value is either an object describing a single violation, or an array of such objects.

Each violation object contains two string-valued members named instanceRef and schemaRef. instanceRef contains the URI fragment serialization of a JSON Pointer to the instance subobject in which the violation was detected. schemaRef contains the URI of the schema and the fragment serialization of a JSON Pointer to the subschema that was violated.

Individual violation objects can contain other keyword-specific members. These are detailed further.

For example, validating this instance:

{"numbers": [1, 2, "3", 4, 5]}

against this schema:

{
  "type": "object",
  "properties": {
    "numbers": {"$ref": "numbers.schema.json"}
  }
}

where numbers.schema.json refers (via a suitable IRemoteSchemaDocumentProvider) to this schema:

{
  "type": "array",
  "items": {"type": "number"}
}

produces the following error object:

{
  "type": {
    "instanceRef": "#/numbers/2",
    "schemaRef": "numbers.schema.json#/items",
    "expected": ["number"],
    "actual": "string"
  }
}

Validation keywords for numbers

multipleOf

• expected: required number strictly greater than 0. The value of the multipleOf keyword specified in the schema.
• actual: required number. The instance value.

maximum

• expected: required number. The value of the maximum keyword specified in the schema.
• exclusiveMaximum: optional boolean. This will be true if the schema specified "exclusiveMaximum": true, and will be omitted otherwise.
• actual: required number. The instance value.

minimum

• expected: required number. The value of the minimum keyword specified in the schema.
• exclusiveMinimum: optional boolean. This will be true if the schema specified "exclusiveMinimum": true, and will be omitted otherwise.
• actual: required number. The instance value.

Validation keywords for strings

maxLength

• expected: required number greater than or equal to 0. The value of the maxLength keyword specified in the schema.
• actual: required string. The instance value.

minLength

• expected: required number greater than or equal to 0. The value of the minLength keyword specified in the schema.
• actual: required string. The instance value.

pattern

• actual: required string. The instance value.

(The expected pattern is not reported because the internal representation in SchemaDocument does not store the pattern in original string form.)

Validation keywords for arrays

additionalItems

This keyword is reported when the value of items schema keyword is an array, the value of additionalItems is false, and the instance is an array with more items than specified in the items array.

• disallowed: required integer greater than or equal to 0. The index of the first item that has no corresponding schema.

maxItems and minItems

• expected: required integer greater than or equal to 0. The value of maxItems (respectively, minItems) specified in the schema.
• actual: required integer greater than or equal to 0. Number of items in the instance array.

uniqueItems

• duplicates: required array whose items are integers greater than or equal to 0. Indices of items of the instance that are equal.

(RapidJSON only reports the first two equal items, for performance reasons.)

Validation keywords for objects

maxProperties and minProperties

• expected: required integer greater than or equal to 0. The value of maxProperties (respectively, minProperties) specified in the schema.
• actual: required integer greater than or equal to 0. Number of properties in the instance object.

required

• missing: required array of one or more unique strings. The names of properties that are listed in the value of the required schema keyword but not present in the instance object.

additionalProperties

This keyword is reported when the schema specifies additionalProperties: false and the name of a property of the instance is neither listed in the properties keyword nor matches any regular expression in the patternProperties keyword.

• disallowed: required string. Name of the offending property of the instance.

(For performance reasons, RapidJSON only reports the first such property encountered.)

dependencies

• errors: required object with one or more properties. Names and values of its properties are described below.

Recall that JSON Schema Draft 04 supports schema dependencies, where presence of a named controlling property requires the instance object to be valid against a subschema, and property dependencies, where presence of a controlling property requires other dependent properties to be also present.

For a violated schema dependency, errors will contain a property with the name of the controlling property and its value will be the error object produced by validating the instance object against the dependent schema.

For a violated property dependency, errors will contain a property with the name of the controlling property and its value will be an array of one or more unique strings listing the missing dependent properties.

Validation keywords for any instance type

enum

This keyword has no additional properties beyond instanceRef and schemaRef.

• The allowed values are not listed because SchemaDocument does not store them in original form.
• The violating value is not reported because it might be unwieldy.

If you need to report these details to your users, you can access the necessary information by following instanceRef and schemaRef.

type

• expected: required array of one or more unique strings, each of which is one of the seven primitive types defined by the JSON Schema Draft 04 Core specification. Lists the types allowed by the type schema keyword.
• actual: required string, also one of seven primitive types. The primitive type of the instance.

allOf, anyOf, and oneOf

• errors: required array of at least one object. There will be as many items as there are subschemas in the allOf, anyOf or oneOf schema keyword, respectively. Each item will be the error value produced by validating the instance against the corresponding subschema.

For allOf, at least one error value will be non-empty. For anyOf, all error values will be non-empty. For oneOf, either all error values will be non-empty, or more than one will be empty.

not

This keyword has no additional properties apart from instanceRef and schemaRef.