fix: keep order of fields with BaseModel.construct() (#2282)

* fix: keep order of fields with `BaseModel.construct()`

closes #2281

* chore: keep extra fields in construct

thanks @layday!

changes/2281-PrettyWood.md

@@ -0,0 +1 @@
+fix: keep order of fields with `BaseModel.construct()`

pydantic/main.py

@@ -611,10 +611,15 @@ class BaseModel(Representation, metaclass=ModelMetaclass):
         """
         Creates a new model setting __dict__ and __fields_set__ from trusted or pre-validated data.
         Default values are respected, but no other validation is performed.
+        Behaves as if `Config.extra = 'allow'` was set since it adds all passed values
         """
         m = cls.__new__(cls)
-        # default field values
-        fields_values = {name: field.get_default() for name, field in cls.__fields__.items() if not field.required}
+        fields_values: Dict[str, Any] = {}
+        for name, field in cls.__fields__.items():
+            if name in values:
+                fields_values[name] = values[name]
+            elif not field.required:
+                fields_values[name] = field.get_default()
         fields_values.update(values)
         object_setattr(m, '__dict__', fields_values)
         if _fields_set is None:

tests/test_construction.py

@@ -35,6 +35,28 @@ def test_construct_fields_set():
     assert m.dict() == {'a': 3, 'b': -1}
 
 
+def test_construct_allow_extra():
+    """construct() should allow extra fields"""
+
+    class Foo(BaseModel):
+        x: int
+
+    assert Foo.construct(x=1, y=2).dict() == {'x': 1, 'y': 2}
+
+
+def test_construct_keep_order():
+    class Foo(BaseModel):
+        a: int
+        b: int = 42
+        c: float
+
+    instance = Foo(a=1, b=321, c=3.14)
+    instance_construct = Foo.construct(**instance.dict())
+    assert instance == instance_construct
+    assert instance.dict() == instance_construct.dict()
+    assert instance.json() == instance_construct.json()
+
+
 def test_large_any_str():
     class Model(BaseModel):
         a: bytes