Adds a configuration option to allow mixed alias/unaliased field name use when deserializing

README.md

@@ -67,6 +67,7 @@ Table of contents
         * [`discriminator` config option](#discriminator-config-option)
         * [`lazy_compilation` config option](#lazy_compilation-config-option)
         * [`sort_keys` config option](#sort_keys-config-option)
+        * [`loose_deserialization` config option](#loose_deserialization-config-option)
     * [Passing field values as is](#passing-field-values-as-is)
     * [Extending existing types](#extending-existing-types)
     * [Dialects](#dialects)
@@ -1391,6 +1392,36 @@ t = SortedDataClass(1, 2)
 assert t.to_dict() == {"bar": 2, "foo": 1}
 ```
 
+#### `loose_deserialization` config option
+
+When using aliases, the deserializer defaults to requiring the keys to match
+what is defined as the alias in the metadata.
+If the flexibility to deserialize aliased and unaliased keys is required then
+the config option `loose_deserialization = True` can be set to enable the
+feature.
+
+```python
+from dataclasses import dataclass, field
+from mashumaro import DataClassDictMixin
+from mashumaro.config import BaseConfig, TO_DICT_ADD_BY_ALIAS_FLAG
+
+@dataclass
+class AliasedDataClass(DataClassDictMixin):
+    foo: int = field(metadata={"alias": "alias_foo"})
+    bar: int = field(metadata={"alias": "alias_bar"})
+
+    class Config(BaseConfig):
+        serialize_by_alias = True
+        loose_deserialization = True
+        code_generation_options = [TO_DICT_ADD_BY_ALIAS_FLAG]
+
+no_alias_dict = {"bar": 2, "foo": 1}
+# Will raise `mashumaro.exceptions.MissingField` if loose_deserialization is
+# False
+t = AliasedDataClass.from_dict(no_alias_dict)
+assert t.to_dict(by_alias=False) == {"bar": 2, "foo": 1}
+```
+
 ### Passing field values as is
 
 In some cases it's needed to pass a field value as is without any changes

mashumaro/config.py

@@ -49,3 +49,4 @@ class BaseConfig:
     discriminator: Optional[Discriminator] = None
     lazy_compilation: bool = False
     sort_keys: bool = False
+    loose_deserialization: bool = False

mashumaro/core/meta/code/builder.py

@@ -554,16 +554,36 @@ def _unpack_method_set_value(
                 could_be_none=False if could_be_none else True,
             )
         )
-        if unpacked_value != "value":
-            self.add_line(f"value = d.get('{alias or fname}', MISSING)")
-            packed_value = "value"
-        elif has_default:
-            self.add_line(f"value = d.get('{alias or fname}', MISSING)")
-            packed_value = "value"
+        if self.get_config().loose_deserialization:
+            if unpacked_value != "value":
+                self.add_line(
+                    f"value = d.get('{alias}', d.get('{fname}', MISSING))"
+                )
+                packed_value = "value"
+            elif has_default:
+                self.add_line(
+                    f"value = d.get('{alias}', d.get('{fname}', MISSING))"
+                )
+                packed_value = "value"
+            else:
+                self.add_line(
+                    f"__{fname} = d.get('{alias}', d.get('{fname}', MISSING))"
+                )
+                packed_value = f"__{fname}"
+                unpacked_value = packed_value
         else:
-            self.add_line(f"__{fname} = d.get('{alias or fname}', MISSING)")
-            packed_value = f"__{fname}"
-            unpacked_value = packed_value
+            if unpacked_value != "value":
+                self.add_line(f"value = d.get('{alias or fname}', MISSING)")
+                packed_value = "value"
+            elif has_default:
+                self.add_line(f"value = d.get('{alias or fname}', MISSING)")
+                packed_value = "value"
+            else:
+                self.add_line(
+                    f"__{fname} = d.get('{alias or fname}', MISSING)"
+                )
+                packed_value = f"__{fname}"
+                unpacked_value = packed_value
         if not has_default:
             with self.indent(f"if {packed_value} is MISSING:"):
                 self.add_line(

tests/test_aliases.py

@@ -176,3 +176,20 @@ class Config(BaseConfig):
 
     assert DataClass(x=123).to_dict() == {"alias": 123}
     assert DataClass(x=None).to_dict() == {"alias": None}
+
+
+def test_by_field_with_loose_deserialize():
+    @dataclass
+    class DataClass(DataClassDictMixin):
+        a: int = field(metadata={"alias": "alias_a"})
+        b: Optional[int] = field(metadata={"alias": "alias_b"})
+
+        class Config(BaseConfig):
+            serialize_by_alias = True
+            code_generation_options = [TO_DICT_ADD_BY_ALIAS_FLAG]
+            loose_deserialization = True
+
+    instance = DataClass(a=123, b=456)
+    assert DataClass.from_dict({"a": 123, "alias_b": 456}) == instance
+    assert instance.to_dict() == {"alias_a": 123, "alias_b": 456}
+    assert instance.to_dict(by_alias=False) == {"a": 123, "b": 456}