✨ Implement root model serialization

src/serializers/type_serializers/function.rs

@@ -140,7 +140,7 @@ impl FunctionPlainSerializer {
                         self.func.call1(py, (model, value))
                     }
                 } else {
-                    Err(PyRuntimeError::new_err("This serializer expected to be run inside the context of a model field but no model field was found"))
+                    Err(PyRuntimeError::new_err("Function plain serializer expected to be run inside the context of a model field but no model was found"))
                 }
             } else if self.info_arg {
                 let info = SerializationInfo::new(py, include, exclude, extra, self.is_field_serializer)?;
@@ -368,7 +368,7 @@ impl FunctionWrapSerializer {
                         self.func.call1(py, (model, value, serialize))
                     }
                 } else {
-                    Err(PyRuntimeError::new_err("This serializer expected to be run inside the context of a model field but no model field was found"))
+                    Err(PyRuntimeError::new_err("Function wrap serializer expected to be run inside the context of a model field but no model was found"))
                 }
             } else if self.info_arg {
                 let info = SerializationInfo::new(py, include, exclude, extra, self.is_field_serializer)?;
@@ -492,20 +492,20 @@ impl SerializationInfo {
     ) -> PyResult<Self> {
         if is_field_serializer {
             match extra.field_name {
-                Some(field_name) => Ok(
-                    Self {
-                        include: include.map(|i| i.into_py(py)),
-                        exclude: exclude.map(|e| e.into_py(py)),
-                        _mode: extra.mode.clone(),
-                        by_alias: extra.by_alias,
-                        exclude_unset: extra.exclude_unset,
-                        exclude_defaults: extra.exclude_defaults,
-                        exclude_none: extra.exclude_none,
-                        round_trip: extra.round_trip,
-                        field_name: Some(field_name.to_string()),
-                    }
-                ),
-                _ => Err(PyRuntimeError::new_err("This serializer expected to be run inside the context of a model field but no model field was found")),
+                Some(field_name) => Ok(Self {
+                    include: include.map(|i| i.into_py(py)),
+                    exclude: exclude.map(|e| e.into_py(py)),
+                    _mode: extra.mode.clone(),
+                    by_alias: extra.by_alias,
+                    exclude_unset: extra.exclude_unset,
+                    exclude_defaults: extra.exclude_defaults,
+                    exclude_none: extra.exclude_none,
+                    round_trip: extra.round_trip,
+                    field_name: Some(field_name.to_string()),
+                }),
+                _ => Err(PyRuntimeError::new_err(
+                    "Model field context expected for field serialization info but no model field was found",
+                )),
             }
         } else {
             Ok(Self {

src/serializers/type_serializers/model.rs

@@ -15,6 +15,8 @@ use super::{
     SerField, TypeSerializer,
 };
 
+const ROOT_FIELD: &str = "root";
+
 pub struct ModelFieldsBuilder;
 
 impl BuildSerializer for ModelFieldsBuilder {
@@ -66,6 +68,7 @@ pub struct ModelSerializer {
     class: Py<PyType>,
     serializer: Box<CombinedSerializer>,
     has_extra: bool,
+    root_model: bool,
     name: String,
 }
 
@@ -85,11 +88,13 @@ impl BuildSerializer for ModelSerializer {
         let class: &PyType = schema.get_as_req(intern!(py, "cls"))?;
         let sub_schema: &PyDict = schema.get_as_req(intern!(py, "schema"))?;
         let serializer = Box::new(CombinedSerializer::build(sub_schema, config, definitions)?);
+        let root_model = schema.get_as(intern!(py, "root_model"))?.unwrap_or(false);
 
         Ok(Self {
             class: class.into(),
             serializer,
             has_extra: has_extra(schema, config)?,
+            root_model,
             name: class.getattr(intern!(py, "__name__"))?.extract()?,
         }
         .into())
@@ -139,11 +144,16 @@ impl TypeSerializer for ModelSerializer {
         exclude: Option<&PyAny>,
         extra: &Extra,
     ) -> PyResult<PyObject> {
-        let extra = Extra {
+        let mut extra = Extra {
             model: Some(value),
             ..*extra
         };
-        if self.allow_value(value, &extra)? {
+        if self.root_model {
+            extra.field_name = Some(ROOT_FIELD);
+            let py = value.py();
+            let root = value.getattr(intern!(py, ROOT_FIELD))?;
+            self.serializer.to_python(root, include, exclude, &extra)
+        } else if self.allow_value(value, &extra)? {
             let inner_value = self.get_inner_value(value, &extra)?;
             self.serializer.to_python(inner_value, include, exclude, &extra)
         } else {
@@ -169,11 +179,17 @@ impl TypeSerializer for ModelSerializer {
         exclude: Option<&PyAny>,
         extra: &Extra,
     ) -> Result<S::Ok, S::Error> {
-        let extra = Extra {
+        let mut extra = Extra {
             model: Some(value),
             ..*extra
         };
-        if self.allow_value(value, &extra).map_err(py_err_se_err)? {
+        if self.root_model {
+            extra.field_name = Some(ROOT_FIELD);
+            let py = value.py();
+            let root = value.getattr(intern!(py, ROOT_FIELD)).map_err(py_err_se_err)?;
+            self.serializer
+                .serde_serialize(root, serializer, include, exclude, &extra)
+        } else if self.allow_value(value, &extra).map_err(py_err_se_err)? {
             let inner_value = self.get_inner_value(value, &extra).map_err(py_err_se_err)?;
             self.serializer
                 .serde_serialize(inner_value, serializer, include, exclude, &extra)

tests/serializers/test_model.py

@@ -857,5 +857,5 @@ class InnerModel:
     s = SchemaSerializer(schema)
     # debug(s)
     s_repr = plain_repr(s)
-    assert 'has_extra:true,name:"InnerModel"' in s_repr
-    assert 'has_extra:false,name:"OuterModel"' in s_repr
+    assert 'has_extra:true,root_model:false,name:"InnerModel"' in s_repr
+    assert 'has_extra:false,root_model:false,name:"OuterModel"' in s_repr

tests/serializers/test_model_root.py

@@ -0,0 +1,131 @@
+import json
+import platform
+from typing import Any
+
+try:
+    from functools import cached_property
+except ImportError:
+    cached_property = None
+
+
+from pydantic_core import SchemaSerializer, core_schema
+
+from ..conftest import plain_repr
+
+on_pypy = platform.python_implementation() == 'PyPy'
+# pypy doesn't seem to maintain order of `__dict__`
+if on_pypy:
+    IsStrictDict = dict
+else:
+    pass
+
+
+class RootModel:
+    __slots__ = 'root'
+    root: str
+
+    def __init__(self, data):
+        self.root = data
+
+
+class RootSubModel(RootModel):
+    pass
+
+
+def test_model_root():
+    s = SchemaSerializer(core_schema.model_schema(RootModel, core_schema.int_schema(), root_model=True))
+    print(plain_repr(s))
+    # TODO: assert 'mode:RootModel' in plain_repr(s)
+    assert 'has_extra:false' in plain_repr(s)
+    assert s.to_python(RootModel(1)) == 1
+    assert s.to_python(RootSubModel(1)) == 1
+
+    j = s.to_json(RootModel(1))
+    if on_pypy:
+        assert json.loads(j) == 1
+    else:
+        assert j == b'1'
+
+    assert json.loads(s.to_json(RootSubModel(1))) == 1
+
+
+def test_function_plain_field_serializer_to_python():
+    class Model(RootModel):
+        def ser_root(self, v: Any, _) -> str:
+            assert self.root == 1_000
+            return f'{v:_}'
+
+    s = SchemaSerializer(
+        core_schema.model_schema(
+            Model,
+            core_schema.int_schema(
+                serialization=core_schema.plain_serializer_function_ser_schema(
+                    Model.ser_root, is_field_serializer=True, info_arg=True
+                )
+            ),
+            root_model=True,
+        )
+    )
+    assert s.to_python(Model(1000)) == '1_000'
+
+
+def test_function_wrap_field_serializer_to_python():
+    class Model(RootModel):
+        def ser_root(self, v: Any, serializer: core_schema.SerializerFunctionWrapHandler, _) -> str:
+            root = serializer(v)
+            assert self.root == 1_000
+            return f'{root:_}'
+
+    s = SchemaSerializer(
+        core_schema.model_schema(
+            Model,
+            core_schema.int_schema(
+                serialization=core_schema.wrap_serializer_function_ser_schema(
+                    Model.ser_root, is_field_serializer=True, info_arg=True, schema=core_schema.any_schema()
+                )
+            ),
+            root_model=True,
+        )
+    )
+    assert s.to_python(Model(1000)) == '1_000'
+
+
+def test_function_plain_field_serializer_to_json():
+    class Model(RootModel):
+        def ser_root(self, v: Any, _) -> str:
+            assert self.root == 1_000
+            return f'{v:_}'
+
+    s = SchemaSerializer(
+        core_schema.model_schema(
+            Model,
+            core_schema.int_schema(
+                serialization=core_schema.plain_serializer_function_ser_schema(
+                    Model.ser_root, is_field_serializer=True, info_arg=True
+                )
+            ),
+            root_model=True,
+        )
+    )
+    assert json.loads(s.to_json(Model(1000))) == '1_000'
+
+
+def test_function_wrap_field_serializer_to_json():
+    class Model(RootModel):
+        def ser_root(self, v: Any, serializer: core_schema.SerializerFunctionWrapHandler, _) -> str:
+            assert self.root == 1_000
+            root = serializer(v)
+            return f'{root:_}'
+
+    s = SchemaSerializer(
+        core_schema.model_schema(
+            Model,
+            core_schema.int_schema(
+                serialization=core_schema.wrap_serializer_function_ser_schema(
+                    Model.ser_root, is_field_serializer=True, info_arg=True, schema=core_schema.any_schema()
+                )
+            ),
+            root_model=True,
+        )
+    )
+    assert json.loads(s.to_json(Model(1000))) == '1_000'

tests/validators/test_model_root.py

@@ -125,3 +125,16 @@ def f(input_value: str, info):
         "ValidationInfo(config=None, context='call 1', field_name='root')",
         "ValidationInfo(config=None, context='assignment call', field_name='root')",
     ]
+
+
+def test_extra():
+    class RootModel:
+        __slots__ = 'root'
+        root: int
+
+    v = SchemaValidator(core_schema.model_schema(RootModel, core_schema.int_schema(), root_model=True))
+
+    m = v.validate_python(1)
+
+    with pytest.raises(AttributeError):
+        m.__pydantic_extra__