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Serializer Hooks
================
.. note::
To customize the load or dump process for annotated types
instead of individual fields, please see the `Type
Hooks <type_hooks.html>`__ section.
You can optionally add hooks that are run before a JSON string or a
Python ``dict`` object is loaded to a dataclass instance, or before the
dataclass instance is converted back to a Python ``dict`` object.
To customize the load process:
* To pre-process data before ``from_dict`` is called, simply
implement a ``_pre_from_dict`` method which will be called
whenever you invoke the ``from_dict`` or ``from_json`` methods.
Please note that this will pass in the original ``dict`` object,
so updating any values will affect data in the underlying ``dict``
(**this might change in a future revision**).
* To post-process data, *after* a dataclass instance is de-serialized,
simply implement the ``__post_init__`` method which will be run
by the ``dataclass`` decorator.
To customize the dump process, simply implement
a ``_pre_dict`` method which will be called
whenever you invoke the ``to_dict`` or ``to_json``
methods. Please note that this will pass in the
original dataclass instance, so updating any values
will affect the fields of the underlying dataclass
(**this might change in a future revision**).
A simple example to illustrate both approaches is shown below:
.. code:: python3
from dataclasses import dataclass
from dataclass_wizard import JSONWizard
from dataclass_wizard.type_def import JSONObject
@dataclass
class MyClass(JSONWizard):
my_str: str
my_int: int
my_bool: bool = False
def __post_init__(self):
self.my_str = self.my_str.title()
self.my_int *= 2
@classmethod
def _pre_from_dict(cls, o: JSONObject) -> JSONObject:
# o = o.copy() # Copying the `dict` object is optional
o['my_bool'] = True # Adds a new key/value pair
return o
def _pre_dict(self):
self.my_str = self.my_str.swapcase()
data = {"my_str": "my string", "myInt": "10"}
c = MyClass.from_dict(data)
print(repr(c))
# prints:
# MyClass(my_str='My String', my_int=20, my_bool=True)
string = c.to_json()
print(string)
# prints:
# {"myStr": "mY sTRING", "myInt": 20, "myBool": true}
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