marshmallow-polyfield 1.0

# mashmallow-polyfield

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An extension to marshmallow to allow for polymorphic fields

Marshmallow is a fantastic library for serialization and deserialization of data.
For more on that project see its [GitHub](https://github.com/marshmallow-code/marshmallow) page or its [Documentation](http://marshmallow.readthedocs.org/en/latest/)

This project adds a custom field designed for polymorphic types. This allows you to define a schema that says "This field accepts anything of type X"

The secret to this field is that you need to define a function that the field can use to deterime what Marshmallow Schema to use for
serialization and deserialization.

An example can be seen in `tests/shapes.py` in `shape_schema_disambiguation`

This function takes in one value which can either be a dictionary in the case of deserialization or an object in the case of serialization.

This function must inspect the object and return the appropriate Schema or raise a `TypeError` if one cannot be found

This field should support the same properties as other Marshmallow fields. I have worked with `required` `allow_none` and `many`.

Below is an example schema using this field.


```
def shape_schema_disambiguation(value):
class_to_schema = {
Rectangle.__name__: RectangleSchema,
Triangle.__name__: TriangleSchema
}
try:
return class_to_schema[value.__class__.__name__]()
except KeyError:
pass

try:
if value.get("base"):
return TriangleSchema()
elif value.get("length"):
return RectangleSchema()
except AttributeError:
pass

raise TypeError("Could not detect type. "
"Did not have a base or a length. "
"Are you sure this is a shape?")

class ContrivedShapeClass(object):
def __init__(self, main, others):
self.main = main
self.others = others

def __eq__(self, other):
return self.__dict__ == other.__dict__

class ContrivedShapeClassSchema(Schema):
main = PolyField(shape_schema_disambiguation, required=True)
others = PolyField(shape_schema_disambiguation, allow_none=True, many=True)

def make_object(self, data):
return TestPolyField.ContrivedShapeClass(
data.get('main'),
data.get('others')
)
```