Implement dataclass for EdgeObject (#359)

Co-authored-by: Yury Selivanov <yury@edgedb.com>

edgedb/datatypes/datatypes.h

@@ -59,6 +59,7 @@ typedef struct {
     EdgeRecordFieldDesc *descs;
     Py_ssize_t idpos;
     Py_ssize_t size;
+    PyObject *get_dataclass_fields_func;
 } EdgeRecordDescObject;
 
 typedef enum {
@@ -82,6 +83,7 @@ EdgeFieldCardinality EdgeRecordDesc_PointerCardinality(PyObject *, Py_ssize_t);
 Py_ssize_t EdgeRecordDesc_GetSize(PyObject *);
 edge_attr_lookup_t EdgeRecordDesc_Lookup(PyObject *, PyObject *, Py_ssize_t *);
 PyObject * EdgeRecordDesc_List(PyObject *, uint8_t, uint8_t);
+PyObject * EdgeRecordDesc_GetDataclassFields(PyObject *);
 
 
 

edgedb/datatypes/object.c

@@ -196,8 +196,18 @@ object_getattr(EdgeObject *o, PyObject *name)
         case L_ERROR:
             return NULL;
 
-        case L_LINKPROP:
         case L_NOT_FOUND:
+            // Used in `dataclasses.as_dict()`
+            if (
+                PyUnicode_CompareWithASCIIString(
+                    name, "__dataclass_fields__"
+                ) == 0
+            ) {
+                return EdgeRecordDesc_GetDataclassFields((PyObject *)o->desc);
+            }
+            return PyObject_GenericGetAttr((PyObject *)o, name);
+
+        case L_LINKPROP:
             return PyObject_GenericGetAttr((PyObject *)o, name);
 
         case L_LINK:
@@ -365,6 +375,16 @@ EdgeObject_InitType(void)
         return NULL;
     }
 
+    // Pass the `dataclasses.is_dataclass(obj)` check - which then checks
+    // `hasattr(type(obj), "__dataclass_fields__")`, the dict is always empty
+    PyObject *default_fields = PyDict_New();
+    if (default_fields == NULL) {
+        return NULL;
+    }
+    PyDict_SetItemString(
+        EdgeObject_Type.tp_dict, "__dataclass_fields__", default_fields
+    );
+
     base_hash = _EdgeGeneric_HashString("edgedb.Object");
     if (base_hash == -1) {
         return NULL;

edgedb/datatypes/record_desc.c

@@ -30,6 +30,7 @@ record_desc_dealloc(EdgeRecordDescObject *o)
     PyObject_GC_UnTrack(o);
     Py_CLEAR(o->index);
     Py_CLEAR(o->names);
+    Py_CLEAR(o->get_dataclass_fields_func);
     PyMem_RawFree(o->descs);
     PyObject_GC_Del(o);
 }
@@ -177,12 +178,24 @@ record_desc_dir(EdgeRecordDescObject *o, PyObject *args)
 }
 
 
+static PyObject *
+record_set_dataclass_fields_func(EdgeRecordDescObject *o, PyObject *arg)
+{
+    Py_CLEAR(o->get_dataclass_fields_func);
+    o->get_dataclass_fields_func = arg;
+    Py_INCREF(arg);
+    Py_RETURN_NONE;
+}
+
+
 static PyMethodDef record_desc_methods[] = {
     {"is_linkprop", (PyCFunction)record_desc_is_linkprop, METH_O, NULL},
     {"is_link", (PyCFunction)record_desc_is_link, METH_O, NULL},
     {"is_implicit", (PyCFunction)record_desc_is_implicit, METH_O, NULL},
     {"get_pos", (PyCFunction)record_desc_get_pos, METH_O, NULL},
     {"__dir__", (PyCFunction)record_desc_dir, METH_NOARGS, NULL},
+    {"set_dataclass_fields_func",
+     (PyCFunction)record_set_dataclass_fields_func, METH_O, NULL},
     {NULL, NULL}
 };
 
@@ -349,6 +362,7 @@ EdgeRecordDesc_New(PyObject *names, PyObject *flags, PyObject *cards)
 
     o->size = size;
     o->idpos = idpos;
+    o->get_dataclass_fields_func = NULL;
 
     PyObject_GC_Track(o);
     return (PyObject *)o;
@@ -537,6 +551,25 @@ EdgeRecordDesc_List(PyObject *ob, uint8_t include_mask, uint8_t exclude_mask)
 }
 
 
+PyObject *
+EdgeRecordDesc_GetDataclassFields(PyObject *ob)
+{
+    if (!EdgeRecordDesc_Check(ob)) {
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+
+    EdgeRecordDescObject *o = (EdgeRecordDescObject *)ob;
+
+// bpo-37194 added PyObject_CallNoArgs() to Python 3.9.0a1
+#if PY_VERSION_HEX < 0x030900A1
+    return PyObject_CallFunctionObjArgs(o->get_dataclass_fields_func, NULL);
+#else
+    return PyObject_CallNoArgs(o->get_dataclass_fields_func);
+#endif
+}
+
+
 PyObject *
 EdgeRecordDesc_InitType(void)
 {

edgedb/protocol/codecs/object.pxd

@@ -19,7 +19,9 @@
 
 @cython.final
 cdef class ObjectCodec(BaseNamedRecordCodec):
-    cdef bint is_sparse
+    cdef:
+        bint is_sparse
+        object cached_dataclass_fields
 
     cdef encode_args(self, WriteBuffer buf, dict obj)
 

edgedb/protocol/codecs/object.pyx

@@ -16,6 +16,8 @@
 # limitations under the License.
 #
 
+import dataclasses
+
 
 @cython.final
 cdef class ObjectCodec(BaseNamedRecordCodec):
@@ -180,6 +182,22 @@ cdef class ObjectCodec(BaseNamedRecordCodec):
 
         return result
 
+    def get_dataclass_fields(self):
+        cdef descriptor = (<BaseNamedRecordCodec>self).descriptor
+
+        rv = self.cached_dataclass_fields
+        if rv is None:
+            rv = {}
+
+            for i in range(len(self.fields_codecs)):
+                name = datatypes.record_desc_pointer_name(descriptor, i)
+                field = rv[name] = dataclasses.field()
+                field.name = name
+                field._field_type = dataclasses._FIELD
+
+            self.cached_dataclass_fields = rv
+        return rv
+
     @staticmethod
     cdef BaseCodec new(bytes tid, tuple names, tuple flags, tuple cards,
                        tuple codecs, bint is_sparse):
@@ -195,6 +213,7 @@ cdef class ObjectCodec(BaseNamedRecordCodec):
             codec.name = 'Object'
         codec.is_sparse = is_sparse
         codec.descriptor = datatypes.record_desc_new(names, flags, cards)
+        codec.descriptor.set_dataclass_fields_func(codec.get_dataclass_fields)
         codec.fields_codecs = codecs
 
         return codec