Add worms.id_type to improve behavior of int ids.

If the project uses numerical IDs, and processes user input from a web
request URL where everything is a string, it is tedious to convert
between str and int on the application side. If done improperly, it
messes up the cache because the int id and str id will be entered
separately. So we let the database handle the id type and raise errors
if necessary.

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)