valid_model
The valid_model library is intended to allow declarative modeling of an object schema in a similar way to various ORM and form validation libraries while making as few assumptions as possible about the way it will be used.
Attributes in a valid_model.Object instance are guaranteed to have all fields exist with defined restrictions and defaults available. In addition each field can have a mutator function applied to it to enforce uniformity. An example of this could be make a String attribute always be uppercase.
You can nest Object classes inside one another using the EmbeddedObject, Set, Dict, and List descriptors
The available descriptors are in valid_model.descriptors and include:
Generic, String, Integer, Float, Bool, DateTime, TimeDelta, List, Set, Dict, and EmbeddedObject
When initializing an Object all initial values should be passed in as keyword arguments.
When setting an EmbeddedObject attribute, it will automatically convert a dict to the appropriate Object subclass.
Object instances have Object.__json__ defined to be used as a hook to convert objects into dict for easy serialization.
class Person(Object):
name = String(nullable=False)
homepage = String()
class BlogPost(Object):
title = String(nullable=False, mutator=lambda x: x.title())
updated = DateTime(nullable=False, default=datetime.utcnow) # default to time object is created
published = DateTime() # default value will be None
author = EmbeddedObject(Person)
contributors = List(value=EmbeddedObject(Person))
tags = List(value=String(nullable=False))
def validate(self):
super(BlogPost, self).validate()
if self.published is not None and self.published > self.updated:
raise ValidationError('a post cannot be published at a later date than it was updated')
post = BlogPost(title='example post', author={'name': 'Josh'}, tags=['tag1', 'tag2'])
"""
post.__json__() would output
{
'title': 'Example Post',
'author': {
'name': 'Josh',
'homepage': None
},
'contributors': [],
'updated': datetime(2014, 10, 6, 10, 23),
'published': None,
'tags': ['tag1', 'tag2']
}
"""Descriptor Options
| Keyword Arg | Default | Description |
|---|---|---|
| nullable |
True1
|
determines if it is valid for an attribute to be set to None |
| mutator | no mutator | allows some mutation to occur on the value. a common use case would be to format a string to always be uppercase |
| validator | no validator | a function which returns truthy if the value is valid |
| default |
None2
|
a scalar value or function which the attribute will be set to on object initialization if no value is specified at in the constuctor |
| value | no descriptor3 | a descriptor to validate values in the container attribute |
| key | no descriptor4 | a descriptor to validate keys in the container attribute |
1 Not available on Set, List, and Dict. If an attribute with that descriptor is set to None it will actually set it to an empty instance of their respective types |
||
2 Container objects Set, List, and Dict initialize to an empty instance of their respective types |
||
3 Only available on Dict, List, and Set
|
||
4 Only available on Dict
|
EmbededObject takes one argument which is the Object class that is being embedded.
How Validation Works
Validation occurs whenever an attribute is set.
- Typechecking and any type coercion implemented occurs
- The value is checked if it is None
- If it is None and nullable == False a ValidationError is raised otherwise it is set to None
- If mutator function is defined it will run
- If a validator function is defined it will run
- A ValidationError is raised if the validator function returns falsey
Complex Validation
In addition to validators being defined on individual attributes there is a validate method on Object instances which may be overridden for more complicated validation logic that may include a combination of multiple fields. By default it will just revalidate all attributes of an Object instance.
