diff --git a/voussoirkit/worms.py b/voussoirkit/worms.py
index 9e17013..ed633cc 100644
--- a/voussoirkit/worms.py
+++ b/voussoirkit/worms.py
@@ -98,6 +98,11 @@ class Database(metaclass=abc.ABCMeta):
         self.on_commit_queue = []
         self.on_rollback_queue = []
         self.savepoints = []
+        # If your IDs are integers, you could change this to int. This way, when
+        # taking user input as strings, they will automatically be converted to
+        # int when querying and caching, and you don't have to do the conversion
+        # on the application side.
+        self.id_type = str
         self.last_commit_id = None
 
     @abc.abstractmethod
@@ -194,6 +199,7 @@ class Database(metaclass=abc.ABCMeta):
         if isinstance(object_id, object_class):
             object_id = object_id.id
 
+        object_id = self.normalize_object_id(object_class, object_id)
         query = f'SELECT * FROM {object_class.table} WHERE id == ?'
         bindings = [object_id]
         object_row = self.select_one(query, bindings)
@@ -231,7 +237,7 @@ class Database(metaclass=abc.ABCMeta):
             we can raise that class's no_such_exception with the set of missing
             IDs.
         '''
-        object_ids = set(object_ids)
+        (object_ids, missing) = self.normalize_object_ids(object_ids)
         ids_needed = list(object_ids)
         ids_found = set()
 
@@ -249,7 +255,7 @@ class Database(metaclass=abc.ABCMeta):
                 yield instance
 
         if raise_for_missing:
-            missing = object_ids.difference(ids_found)
+            missing.update(object_ids.difference(ids_found))
             if missing:
                 raise object_class.no_such_exception(missing)
 
@@ -280,6 +286,42 @@ class Database(metaclass=abc.ABCMeta):
         query = f'INSERT INTO {table} VALUES({qmarks})'
         return self.execute(query, bindings)
 
+    def normalize_object_id(self, object_class, object_id):
+        '''
+        Given an object ID as input by the user, try to convert it using
+        self.id_type. If that raises a ValueError, then we raise
+        that class's no_such_exception.
+
+        Just because an ID passes the type conversion does not mean that ID
+        actually exists. We can raise the no_such_exception because an invalid
+        ID certainly doesn't exist, but a valid one still might not exist.
+        '''
+        try:
+            return self.id_type(object_id)
+        except ValueError:
+            raise object_class.no_such_exception(object_id)
+
+    def normalize_object_ids(self, object_ids):
+        '''
+        Given a list of object ids, return two sets: the first set contains all
+        the IDs that were able to be normalized using self.id_type; the second
+        contains all the IDs that raised ValueError. This method does not raise
+        the no_such_exception. as you may prefer to process the good instead of
+        losing it all with an exception.
+
+        Just because an ID passes the type conversion does not mean that ID
+        actually exists.
+        '''
+        good = set()
+        bad = set()
+        for object_id in object_ids:
+            try:
+                good.add(self.id_type(object_id))
+            except ValueError:
+                bad.add(object_id)
+
+        return (good, bad)
+
     def release_savepoint(self, savepoint, allow_commit=False) -> None:
         '''
         Releasing a savepoint removes that savepoint from the timeline, so that
@@ -465,6 +507,7 @@ class DatabaseWithCaching(Database, metaclass=abc.ABCMeta):
             # Probably an uncommon need but... no harm I think.
             object_id = object_id.id
 
+        object_id = self.normalize_object_id(object_class, object_id)
         object_cache = self.caches.get(object_class, None)
 
         if object_cache is not None:
@@ -520,7 +563,7 @@ class DatabaseWithCaching(Database, metaclass=abc.ABCMeta):
         '''
         object_cache = self.caches.get(object_class, None)
 
-        object_ids = set(object_ids)
+        (object_ids, missing) = self.normalize_object_ids(object_ids)
         ids_needed = set()
         ids_found = set()
 
@@ -563,7 +606,7 @@ class DatabaseWithCaching(Database, metaclass=abc.ABCMeta):
                 yield instance
 
         if raise_for_missing:
-            missing = object_ids.difference(ids_found)
+            missing.update(object_ids.difference(ids_found))
             if missing:
                 raise object_class.no_such_exception(missing)