Schema Validation

There are two helper methods to verify schemas and interfaces:

getValidationErrors()
first validates via the zope.schema field validators. If that succeeds the invariants are checked.
getSchemaValidationErrors()
only validates via the zope.schema field validators. The invariants are not checked.

Create an interface to validate against:

>>> import zope.interface
>>> import zope.schema
>>> _a_greater_b_called = []
>>> class ITwoInts(zope.interface.Interface):
...     a = zope.schema.Int(max=10)
...     b = zope.schema.Int(min=5)
...
...     @zope.interface.invariant
...     def a_greater_b(obj):
...         _a_greater_b_called.append(obj)
...         if obj.a <= obj.b:
...             raise zope.interface.Invalid("%s<=%s" % (obj.a, obj.b))
...

Create a silly model:

>>> class TwoInts(object):
...     pass

Create an instance of TwoInts but do not set attributes. We get two errors:

>>> ti = TwoInts()
>>> r = zope.schema.getValidationErrors(ITwoInts, ti)
>>> r.sort()
>>> len(r)
2
>>> r[0][0]
'a'
>>> r[0][1].__class__.__name__
'SchemaNotFullyImplemented'
>>> r[0][1].args[0].args
("'TwoInts' object has no attribute 'a'",)
>>> r[1][0]
'b'
>>> r[1][1].__class__.__name__
'SchemaNotFullyImplemented'
>>> r[1][1].args[0].args
("'TwoInts' object has no attribute 'b'",)

The getSchemaValidationErrors function returns the same result:

>>> r = zope.schema.getSchemaValidationErrors(ITwoInts, ti)
>>> r.sort()
>>> len(r)
2
>>> r[0][0]
'a'
>>> r[0][1].__class__.__name__
'SchemaNotFullyImplemented'
>>> r[0][1].args[0].args
("'TwoInts' object has no attribute 'a'",)
>>> r[1][0]
'b'
>>> r[1][1].__class__.__name__
'SchemaNotFullyImplemented'
>>> r[1][1].args[0].args
("'TwoInts' object has no attribute 'b'",)

Note that see no error from the invariant because the invariants are not validated if there are other schema errors.

When we set a valid value for a we still get the same error for b:

>>> ti.a = 11
>>> errors = zope.schema.getValidationErrors(ITwoInts, ti)
>>> errors.sort()
>>> len(errors)
2
>>> errors[0][0]
'a'
>>> print(errors[0][1].doc())
Value is too big
>>> errors[0][1].__class__.__name__
'TooBig'
>>> errors[0][1].args
(11, 10)
>>> errors[1][0]
'b'
>>> errors[1][1].__class__.__name__
'SchemaNotFullyImplemented'
>>> errors[1][1].args[0].args
("'TwoInts' object has no attribute 'b'",)

After setting a valid value for a there is only the error for the missing b left:

>>> ti.a = 8
>>> r = zope.schema.getValidationErrors(ITwoInts, ti)
>>> r
[('b', SchemaNotFullyImplemented(...AttributeError...))]
>>> r[0][1].args[0].args
("'TwoInts' object has no attribute 'b'",)

After setting valid value for b the schema is valid so the invariants are checked. As b>a the invariant fails:

>>> ti.b = 10
>>> errors = zope.schema.getValidationErrors(ITwoInts, ti)
>>> len(errors)
1
>>> errors[0][0] is None
True
>>> errors[0][1].__class__.__name__
'Invalid'
>>> len(_a_greater_b_called)
1

When using getSchemaValidationErrors we do not get an error any more:

>>> zope.schema.getSchemaValidationErrors(ITwoInts, ti)
[]

Set b=5 so everything is fine:

>>> ti.b = 5
>>> del _a_greater_b_called[:]
>>> zope.schema.getValidationErrors(ITwoInts, ti)
[]
>>> len(_a_greater_b_called)
1

Compare ValidationError

There was an issue with compare validation error with something else then an exceptions. Let’s test if we can compare ValidationErrors with different things

>>> from zope.schema._bootstrapinterfaces import ValidationError
>>> v1 = ValidationError('one')
>>> v2 = ValidationError('one')
>>> v3 = ValidationError('another one')

A ValidationError with the same arguments compares:

>>> v1 == v2
True

but not with an error with different arguments:

>>> v1 == v3
False

We can also compare validation errors with other things then errors. This was running into an AttributeError in previous versions of zope.schema. e.g. AttributeError: ‘NoneType’ object has no attribute ‘args’

>>> v1 == None
False
>>> v1 == object()
False
>>> v1 == False
False
>>> v1 == True
False
>>> v1 == 0
False
>>> v1 == 1
False
>>> v1 == int
False

If we compare a ValidationError with another validation error based class, we will get the following result:

>>> from zope.schema._bootstrapinterfaces import RequiredMissing
>>> r1 = RequiredMissing('one')
>>> v1 == r1
True