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Let data_key and attribute default to field name #1897

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Let data_key and attribute default to field name #1897

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747f364
Let data_key default to field name
lafrech Oct 27, 2021
f61370c
typing.cast field_obj.data_key
lafrech Oct 27, 2021
43b0bc7
Add data_key to Field.__repr__
lafrech Oct 28, 2021
1feec81
Let attribute default to field name
lafrech Oct 28, 2021
a53475a
typing.cast field_obj.attribute
lafrech Oct 28, 2021
0d12e42
Rename local variables in Schema methods
lafrech Oct 28, 2021
a300e1c
Set field names on Schema creation
lafrech Oct 28, 2021
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3 changes: 2 additions & 1 deletion src/marshmallow/fields.py
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Original file line number Diff line number Diff line change
Expand Up @@ -377,6 +377,7 @@ def _bind_to_schema(self, field_name, schema):
"""
self.parent = self.parent or schema
self.name = self.name or field_name
self.data_key = self.data_key if self.data_key is not None else field_name
self.root = self.root or (
self.parent.root if isinstance(self.parent, FieldABC) else self.parent
)
Expand Down Expand Up @@ -688,7 +689,7 @@ def __init__(
@property
def _field_data_key(self):
only_field = self.schema.fields[self.field_name]
return only_field.data_key or self.field_name
return only_field.data_key

def _serialize(self, nested_obj, attr, obj, **kwargs):
ret = super()._serialize(nested_obj, attr, obj, **kwargs)
Expand Down
21 changes: 5 additions & 16 deletions src/marshmallow/schema.py
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Original file line number Diff line number Diff line change
Expand Up @@ -520,8 +520,7 @@ def _serialize(
value = field_obj.serialize(attr_name, obj, accessor=self.get_attribute)
if value is missing:
continue
key = field_obj.data_key if field_obj.data_key is not None else attr_name
ret[key] = value
ret[field_obj.data_key] = value
return ret

def dump(self, obj: typing.Any, *, many: typing.Optional[bool] = None):
Expand Down Expand Up @@ -634,9 +633,7 @@ def _deserialize(
else:
partial_is_collection = is_collection(partial)
for attr_name, field_obj in self.load_fields.items():
field_name = (
field_obj.data_key if field_obj.data_key is not None else attr_name
)
field_name = field_obj.data_key
raw_value = data.get(field_name, missing)

@deckar01 deckar01 Oct 27, 2021 •
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error: Argument 1 to "get" of "Mapping" has incompatible type "Optional[str]"; expected "str"

The problem is that Fields.__init__ assigned a Optional[str] type to data_key. _bind_to_schema guarantees that field_obj.data_key is a str, but the type checker doesn't know that _deserialize is guaranteed to run after _bind_to_schema. I guess the get type annotation enforces this argument, but AFAICT, None doesn't actually error. 🤷

It wants you to ensure data_key is never None. The only thing I can think of is to make data_key a @property that raises an exception if the field is unbound.

@lafrech lafrech Oct 27, 2021

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Yes, we agree on the reason behind the error.

It would be a shame to "complicate" the code, even slightly, to please the linter.

I suppose we could add comments to skip test on each failing line, but I'd rather find a way to centralize that by somehow forcing the type of self.data_key once and for all.

We could use a cast:

self.data_key = typing.cast(str, data_key)

but doing this in __init__ before field binding would be wrong.

Or we do it just before the type check error:

field_name = typing.cast(str, field_obj.data_key)

Still not ideal because:

  • It is not done everywhere, only where the error was triggered. Other errors may occur later here or in other libs.
  • It is executed on each deserialization, although IIUC it is neglectable.

I just pushed a commit doing that.

if raw_value is missing:
# Ignore missing field if we're allowed to.
Expand Down Expand Up @@ -669,10 +666,7 @@ def _deserialize(
key = field_obj.attribute or attr_name
set_value(ret_d, key, value)
if unknown != EXCLUDE:
fields = {
field_obj.data_key if field_obj.data_key is not None else field_name
for field_name, field_obj in self.load_fields.items()
}
fields = {field_obj.data_key for field_obj in self.load_fields.values()}
for key in set(data) - fields:
value = data[key]
if unknown == INCLUDE:
Expand Down Expand Up @@ -986,10 +980,7 @@ def _init_fields(self) -> None:
if not field_obj.load_only:
dump_fields[field_name] = field_obj

dump_data_keys = [
field_obj.data_key if field_obj.data_key is not None else name
for name, field_obj in dump_fields.items()
]
dump_data_keys = [field_obj.data_key for field_obj in dump_fields.values()]
if len(dump_data_keys) != len(set(dump_data_keys)):
data_keys_duplicates = {
x for x in dump_data_keys if dump_data_keys.count(x) > 1
Expand Down Expand Up @@ -1110,9 +1101,7 @@ def _invoke_field_validators(self, *, error_store: ErrorStore, data, many: bool)
continue
raise ValueError(f'"{field_name}" field does not exist.') from error

data_key = (
field_obj.data_key if field_obj.data_key is not None else field_name
)
data_key = field_obj.data_key
if many:
for idx, item in enumerate(data):
try:
Expand Down
9 changes: 9 additions & 0 deletions tests/test_fields.py
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Original file line number Diff line number Diff line change
Expand Up @@ -92,6 +92,15 @@ class MySchema(Schema):
result = MySchema().dump({"name": "Monty", "foo": 42})
assert result == {"_NaMe": "Monty"}

def test_data_key_defaults_to_field_name(self):
class MySchema(Schema):
field_1 = fields.String(data_key="field_one")
field_2 = fields.String()

schema_fields = MySchema().fields
assert schema_fields["field_1"].data_key == "field_one"
assert schema_fields["field_2"].data_key == "field_2"


class TestParentAndName:
class MySchema(Schema):
Expand Down