use classmethod to build fields on records

src/grung/examples.py

@@ -2,8 +2,12 @@ from grung.types import Collection, Field, Integer, Record
 
 
 class User(Record):
-    _fields = [Field("name"), Integer("number", default=0), Field("email", unique=True)]
+    @classmethod
+    def fields(cls):
+        return [*super().fields(), Field("name"), Integer("number", default=0), Field("email", unique=True)]
 
 
 class Group(Record):
-    _fields = [Field("name", unique=True), Collection("users", User)]
+    @classmethod
+    def fields(cls):
+        return [*super().fields(), Field("name", unique=True), Collection("members", User), Collection("groups", cls)]

src/grung/types.py

@@ -1,11 +1,11 @@
 from __future__ import annotations
 
 from collections import namedtuple
-from dataclasses import dataclass
+from dataclasses import dataclass, field
 from typing import Dict, List
 
 import nanoid
-from tinydb import where
+from tinydb import TinyDB, where
 
 from grung.exceptions import PointerReferenceError
 
@@ -18,23 +18,21 @@ class Field:
     Represents a single field in a Record.
     """
 
-    value_type = str
-
     name: str
-    default: value_type | None = None
+    value_type: type = str
+    default: str = None
     unique: bool = False
 
     def serialize(self, rec: value_type, db: TinyDB) -> str:
         return str(rec)
 
-    def deserialize(self, rec: str, db: TinyDB) -> value_type:
+    def deserialize(self, rec: value_type, db: TinyDB) -> value_type:
         return rec
 
 
+@dataclass
 class Integer(Field):
-    value_type = int
+    default: int = 0
-
-    default: value_type = 0
 
     def deserialize(self, rec: str, db: TinyDB) -> value_type:
         return int(rec)
@@ -46,14 +44,17 @@ class Record(Dict[(str, Field)]):
     """
 
     def __init__(self, raw_doc: dict = {}, doc_id: int = None, **params):
-        # populate the metadata
+        self.doc_id = doc_id
-        self._fields.append(
+        fields = self.__class__.fields()
+        self._metadata = Metadata(table=self.__class__.__name__, fields={f.name: f for f in fields})
+        super().__init__(dict({field.name: field.default for field in fields}, **raw_doc, **params))
+
+    @classmethod
+    def fields(self):
+        return [
             # 1% collision rate at ~2M records
             Field("uid", default=nanoid.generate(size=8), unique=True)
-        )
+        ]
-        self._metadata = Metadata(table=self.__class__.__name__, fields={f.name: f for f in self._fields})
-        self.doc_id = doc_id
-        super().__init__(dict({field.name: field.default for field in self._fields}, **raw_doc, **params))
 
     def serialize(self, db):
         """
@@ -83,26 +84,32 @@ class Record(Dict[(str, Field)]):
             return self.get(attr_name)
         return super().__getattr__(attr_name)
 
+    def __hash__(self):
+        return hash(str(dict(self)))
+
     def __repr__(self):
         return f"{self.__class__.__name__}[{self.doc_id}]: {self.items()}"
 
 
+@dataclass
 class Collection(Field):
     """
     A collection of fields that store pointers instead of dicts.
     """
 
-    value_type = List[Record]
+    value_type: type = Record
+    default: List[value_type] = field(default_factory=lambda: [])
 
-    def serialize(self, recs: value_type, db: TinyDB) -> List[str]:
+    def serialize(self, value: value_type, db: TinyDB) -> List[str]:
-        vals = []
+        vals = self.default
-        for rec in recs:
+        if value:
-            if not rec.doc_id:
+            for rec in value:
-                raise PointerReferenceError(rec)
+                if not rec.doc_id:
-            vals.append(f"{rec._metadata.table}::{rec.uid}")
+                    raise PointerReferenceError(rec)
+                vals.append(f"{rec._metadata.table}::{rec.uid}")
         return vals
 
-    def deserialize(self, rec: List[str], db: TinyDB) -> Collection.value_type:
+    def deserialize(self, rec: List[value_type], db: TinyDB) -> value_type:
         """
         Recursively deserialize the objects in this collection
         """

test/test_db.py

@@ -43,16 +43,29 @@ def test_crud(db):
 
 def test_pointers(db):
     user = examples.User(name="john", email="john@foo")
-    players = examples.Group(name="players", users=[user])
+    players = examples.Group(name="players", members=[user], groups=[])
 
     with pytest.raises(PointerReferenceError):
         players = db.save(players)
 
     user = db.save(user)
 
-    players.users[0] = user
+    players.members[0] = user
     players = db.save(players)
-    assert players.users[0] == user
+    assert players.members[0] == user
+
+
+def test_subgroups(db):
+    kirk = db.save(examples.User(name="James T. Kirk", email="riskybiznez@starfleet"))
+    pike = db.save(examples.User(name="Christopher Pike", email="hitit@starfleet"))
+
+    tos = db.save(examples.Group(name="The Original Series", members=[kirk]))
+    snw = db.save(examples.Group(name="Strange New Worlds", members=[pike]))
+
+    starfleet = db.save(examples.Group(name="Starfleet", groups=[tos, snw]))
+    assert tos in starfleet.groups
+    assert snw in starfleet.groups
+    assert kirk in set([user for group in starfleet.groups for user in group.members])
 
 
 def test_unique(db):