========================== Handling Validation Errors ========================== .. currentmodule:: jsonschema.exceptions When an invalid instance is encountered, a `ValidationError` will be raised or returned, depending on which method or function is used. .. autoexception:: ValidationError :noindex: The information carried by an error roughly breaks down into: =============== ================= ======================== What Happened Why Did It Happen What Was Being Validated =============== ================= ======================== `message` `context` `instance` `cause` `json_path` `path` `schema` `schema_path` `validator` `validator_value` =============== ================= ======================== .. attribute:: message A human readable message explaining the error. .. attribute:: validator The name of the failed `keyword `_. .. attribute:: validator_value The associated value for the failed keyword in the schema. .. attribute:: schema The full schema that this error came from. This is potentially a subschema from within the schema that was passed in originally, or even an entirely different schema if a :kw:`$ref` was followed. .. attribute:: relative_schema_path A `collections.deque` containing the path to the failed keyword within the schema. .. attribute:: absolute_schema_path A `collections.deque` containing the path to the failed keyword within the schema, but always relative to the *original* schema as opposed to any subschema (i.e. the one originally passed into a validator class, *not* `schema`\). .. attribute:: schema_path Same as `relative_schema_path`. .. attribute:: relative_path A `collections.deque` containing the path to the offending element within the instance. The deque can be empty if the error happened at the root of the instance. .. attribute:: absolute_path A `collections.deque` containing the path to the offending element within the instance. The absolute path is always relative to the *original* instance that was validated (i.e. the one passed into a validation method, *not* `instance`\). The deque can be empty if the error happened at the root of the instance. .. attribute:: json_path A `JSON path `_ to the offending element within the instance. .. attribute:: path Same as `relative_path`. .. attribute:: instance The instance that was being validated. This will differ from the instance originally passed into ``validate`` if the validator object was in the process of validating a (possibly nested) element within the top-level instance. The path within the top-level instance (i.e. `ValidationError.path`) could be used to find this object, but it is provided for convenience. .. attribute:: context If the error was caused by errors in subschemas, the list of errors from the subschemas will be available on this property. The `schema_path` and `path` of these errors will be relative to the parent error. .. attribute:: cause If the error was caused by a *non*-validation error, the exception object will be here. Currently this is only used for the exception raised by a failed format checker in `jsonschema.FormatChecker.check`. .. attribute:: parent A validation error which this error is the `context` of. ``None`` if there wasn't one. In case an invalid schema itself is encountered, a `SchemaError` is raised. .. autoexception:: SchemaError :noindex: The same attributes are present as for `ValidationError`\s. These attributes can be clarified with a short example: .. testcode:: schema = { "items": { "anyOf": [ {"type": "string", "maxLength": 2}, {"type": "integer", "minimum": 5} ] } } instance = [{}, 3, "foo"] v = Draft202012Validator(schema) errors = sorted(v.iter_errors(instance), key=lambda e: e.path) The error messages in this situation are not very helpful on their own. .. testcode:: for error in errors: print(error.message) outputs: .. testoutput:: {} is not valid under any of the given schemas 3 is not valid under any of the given schemas 'foo' is not valid under any of the given schemas If we look at `ValidationError.path` on each of the errors, we can find out which elements in the instance correspond to each of the errors. In this example, `ValidationError.path` will have only one element, which will be the index in our list. .. testcode:: for error in errors: print(list(error.path)) .. testoutput:: [0] [1] [2] Since our schema contained nested subschemas, it can be helpful to look at the specific part of the instance and subschema that caused each of the errors. This can be seen with the `ValidationError.instance` and `ValidationError.schema` attributes. With keywords like :kw:`anyOf`, the `ValidationError.context` attribute can be used to see the sub-errors which caused the failure. Since these errors actually came from two separate subschemas, it can be helpful to look at the `ValidationError.schema_path` attribute as well to see where exactly in the schema each of these errors come from. In the case of sub-errors from the `ValidationError.context` attribute, this path will be relative to the `ValidationError.schema_path` of the parent error. .. testcode:: for error in errors: for suberror in sorted(error.context, key=lambda e: e.schema_path): print(list(suberror.schema_path), suberror.message, sep=", ") .. testoutput:: [0, 'type'], {} is not of type 'string' [1, 'type'], {} is not of type 'integer' [0, 'type'], 3 is not of type 'string' [1, 'minimum'], 3 is less than the minimum of 5 [0, 'maxLength'], 'foo' is too long [1, 'type'], 'foo' is not of type 'integer' The string representation of an error combines some of these attributes for easier debugging. .. testcode:: print(errors[1]) .. testoutput:: 3 is not valid under any of the given schemas Failed validating 'anyOf' in schema['items']: {'anyOf': [{'maxLength': 2, 'type': 'string'}, {'minimum': 5, 'type': 'integer'}]} On instance[1]: 3 ErrorTrees ---------- If you want to programmatically query which validation keywords failed when validating a given instance, you may want to do so using `jsonschema.exceptions.ErrorTree` objects. .. autoclass:: jsonschema.exceptions.ErrorTree :noindex: :members: :special-members: :exclude-members: __dict__,__weakref__ .. attribute:: errors The mapping of validation keywords to the error objects (usually `jsonschema.exceptions.ValidationError`\s) at this level of the tree. Consider the following example: .. testcode:: schema = { "type" : "array", "items" : {"type" : "number", "enum" : [1, 2, 3]}, "minItems" : 3, } instance = ["spam", 2] For clarity's sake, the given instance has three errors under this schema: .. testcode:: v = Draft202012Validator(schema) for error in sorted(v.iter_errors(["spam", 2]), key=str): print(error.message) .. testoutput:: 'spam' is not of type 'number' 'spam' is not one of [1, 2, 3] ['spam', 2] is too short Let's construct an `jsonschema.exceptions.ErrorTree` so that we can query the errors a bit more easily than by just iterating over the error objects. .. testcode:: from jsonschema.exceptions import ErrorTree tree = ErrorTree(v.iter_errors(instance)) As you can see, `jsonschema.exceptions.ErrorTree` takes an iterable of `ValidationError`\s when constructing a tree so you can directly pass it the return value of a validator's `jsonschema.protocols.Validator.iter_errors` method. `ErrorTree`\s support a number of useful operations. The first one we might want to perform is to check whether a given element in our instance failed validation. We do so using the :keyword:`in` operator: .. doctest:: >>> 0 in tree True >>> 1 in tree False The interpretation here is that the 0th index into the instance (``"spam"``) did have an error (in fact it had 2), while the 1th index (``2``) did not (i.e. it was valid). If we want to see which errors a child had, we index into the tree and look at the `ErrorTree.errors` attribute. .. doctest:: >>> sorted(tree[0].errors) ['enum', 'type'] Here we see that the :kw:`enum` and :kw:`type` keywords failed for index ``0``. In fact `ErrorTree.errors` is a dict, whose values are the `ValidationError`\s, so we can get at those directly if we want them. .. doctest:: >>> print(tree[0].errors["type"].message) 'spam' is not of type 'number' Of course this means that if we want to know if a given validation keyword failed for a given index, we check for its presence in `ErrorTree.errors`: .. doctest:: >>> "enum" in tree[0].errors True >>> "minimum" in tree[0].errors False Finally, if you were paying close enough attention, you'll notice that we haven't seen our :kw:`minItems` error appear anywhere yet. This is because :kw:`minItems` is an error that applies globally to the instance itself. So it appears in the root node of the tree. .. doctest:: >>> "minItems" in tree.errors True That's all you need to know to use error trees. To summarize, each tree contains child trees that can be accessed by indexing the tree to get the corresponding child tree for a given index into the instance. Each tree and child has a `ErrorTree.errors` attribute, a dict, that maps the failed validation keyword to the corresponding validation error. best_match and relevance ------------------------ The `best_match` function is a simple but useful function for attempting to guess the most relevant error in a given bunch. .. doctest:: >>> from jsonschema import Draft202012Validator >>> from jsonschema.exceptions import best_match >>> schema = { ... "type": "array", ... "minItems": 3, ... } >>> print(best_match(Draft202012Validator(schema).iter_errors(11)).message) 11 is not of type 'array' .. autofunction:: best_match :noindex: .. function:: relevance(validation_error) :noindex: A key function that sorts errors based on heuristic relevance. If you want to sort a bunch of errors entirely, you can use this function to do so. Using this function as a key to e.g. `sorted` or `max` will cause more relevant errors to be considered greater than less relevant ones. Within the different validation keywords that can fail, this function considers :kw:`anyOf` and :kw:`oneOf` to be *weak* validation errors, and will sort them lower than other errors at the same level in the instance. If you want to change the set of weak [or strong] validation keywords you can create a custom version of this function with `by_relevance` and provide a different set of each. .. doctest:: >>> schema = { ... "properties": { ... "name": {"type": "string"}, ... "phones": { ... "properties": { ... "home": {"type": "string"} ... }, ... }, ... }, ... } >>> instance = {"name": 123, "phones": {"home": [123]}} >>> errors = Draft202012Validator(schema).iter_errors(instance) >>> [ ... e.path[-1] ... for e in sorted(errors, key=exceptions.relevance) ... ] ['home', 'name'] .. autofunction:: by_relevance :noindex: