Fix nested partial to use attr_name instead of data_key for prefix#2903
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sloria merged 4 commits intomarshmallow-code:devfrom Mar 25, 2026
Merged
Fix nested partial to use attr_name instead of data_key for prefix#2903sloria merged 4 commits intomarshmallow-code:devfrom
sloria merged 4 commits intomarshmallow-code:devfrom
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When building dot-delimited sub_partial for nested schemas, the prefix
was computed from field_name (which is data_key when set) instead of
attr_name. Since users specify partial fields using attribute names like
partial=("nested_field.child",), the prefix needs to match attr_name.
When data_key differs from attr_name, the prefix mismatch caused the
nested partial list to always be empty, so the nested schema never
received the partial option and required fields raised unexpected
validation errors.
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sloria
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Feb 20, 2026
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Can you please add a test to demonstrate the issue/fix?
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Summary
When using dot-delimited
partialwith nested schemas, the sub-partial prefix is derived fromfield_name(thedata_key) instead ofattr_name. This causes the nested partial to silently break when a field hasdata_keyset.Problem
The
partialparameter accepts dot-delimited attribute names:In
_deserialize, the top-level partial check correctly usesattr_name:But the nested sub-partial extraction uses
field_name(which is thedata_keyif set):If a field is declared as
address = Nested(AddressSchema, data_key="homeAddress"), then:attr_name="address"field_name="homeAddress"(from data_key)partial=("address.zip_code",)prefix="homeAddress."— doesn't match"address.zip_code"sub_partialis empty, nested schema doesn't getpartialFix
Use
attr_nameinstead offield_namefor the prefix, consistent with how the top-level partial check works.