implement unique constraint checking

src/grung/db.py

@@ -1,8 +1,11 @@
 import inspect
+from functools import reduce
+from operator import ior
 
-from tinydb import TinyDB, table
+from tinydb import Query, TinyDB, table
 from tinydb.table import Document
 
+from grung.exceptions import UniqueConstraintError
 from grung.types import Record
 
 
@@ -11,9 +14,10 @@ class RecordTable(table.Table):
     Wrapper around tinydb Tables that handles Records instead of dicts.
     """
 
-    def __init__(self, storage, name, document_class: Document = Record, **kwargs):
+    def __init__(self, name: str, db: TinyDB, document_class: Document = Record, **kwargs):
         self.document_class = document_class
-        super().__init__(storage, name, **kwargs)
+        self._db = db
+        super().__init__(db.storage, name, **kwargs)
 
     def insert(self, document):
         self._satisfy_constraints(document)
@@ -27,9 +31,26 @@ class RecordTable(table.Table):
         if document.doc_id:
             super().remove(doc_ids=[document.doc_id])
 
-    def _satisfy_constraints(self, document):
-        # check for uniqueness, etc.
-        pass
+    def _satisfy_constraints(self, document) -> bool:
+        self._check_unique(document)
+
+    def _check_unique(self, document) -> bool:
+        matches = [
+            match
+            for match in self.search(
+                reduce(
+                    ior,
+                    [
+                        Query().fragment({field.name: document[field.name]})
+                        for field in document._metadata.fields.values()
+                        if field.unique
+                    ],
+                )
+            )
+            if match.doc_id != document.doc_id
+        ]
+        if matches != []:
+            raise UniqueConstraintError(document, matches)
 
 
 class GrungDB(TinyDB):
@@ -53,7 +74,7 @@ class GrungDB(TinyDB):
     def create_table(self, table_class):
         name = table_class.__name__
         if name not in self._tables:
-            self._tables[name] = RecordTable(self.storage, name, document_class=table_class)
+            self._tables[name] = RecordTable(name, db=self, document_class=table_class)
         return self.table(name)
 
     def save(self, record):

src/grung/exceptions.py

@@ -0,0 +1,12 @@
+class UniqueConstraintError(Exception):
+    """
+    Thrown when a db write operation cannot complete due to a field's unique constraint.
+    """
+
+    def __init__(self, document, collisions):
+        super().__init__(
+            "\n"
+            f"  * Record:  {dict(document)}\n"
+            f"  * Error:   Unique constraint failure\n"
+            "   * The record matches the following existing records:\n\n" + "\n".join(str(c) for c in collisions)
+        )