db: Create a new Child class

This inherites from the Table, but takes a parent instance for some
functions and calculates offsets for items that descend from this
parent.

Implements: Issue #1 (Have SQLite sort our sidebar tables)
Signed-off-by: Anna Schumaker <Anna@NoWheyCreamery.com>

db/table.py

@@ -87,3 +87,31 @@ class Model(GObject.GObject, Gio.ListModel, Table):
         n = self.get_n_items()
         super().reset()
         self.emit("items-changed", 0, n, self.get_n_items())
+
+
+class Child(Table):
+    def __init__(self, table, parent, order):
+        Table.__init__(self, table)
+        self.parent = parent
+        self.order = order
+
+    def get_n_children(self, parent):
+        cur = sql.execute(f"SELECT COUNT(*) FROM {self.table} "
+                          f"WHERE {self.parent}=?", [ parent.rowid ])
+        return cur.fetchone()[0]
+
+    def get_child(self, parent, n):
+        cur = sql.execute(f"SELECT * FROM {self.table} WHERE {self.parent}=? "
+                          f"ORDER BY {self.order} LIMIT 1 OFFSET ?",
+                                [ parent.rowid, n ])
+        return self.factory(cur.fetchone())
+
+    def get_child_index(self, parent, child):
+        cur = sql.execute(f"SELECT * FROM (SELECT rowid,ROW_NUMBER() "
+                                             f"OVER (ORDER BY {self.order}) "
+                                             f"FROM {self.table} "
+                                             f"WHERE {self.parent}=?)"
+                          f"WHERE rowid=?", [ parent.rowid, child.rowid ])
+        return cur.fetchone()[1] - 1
+
+    def find(self, *args): raise NotImplementedError

db/test_table.py

@@ -34,6 +34,24 @@ class FakeModel(table.Model, FakeTable):
         table.Model.__init__(self, "fake_table", "lower(name)")
         self.reset()
 
+class FakeChild(table.Child):
+    def __init__(self):
+        table.Child.__init__(self, "fake_child", "parentid", "lower(name)")
+        self.reset()
+
+    def do_create(self):
+        sql.execute("CREATE TABLE IF NOT EXISTS fake_child "
+                        "(fakeid INTEGER PRIMARY KEY, "
+                         "parentid INTEGER, "
+                         "name TEXT UNIQUE, "
+                         "FOREIGN KEY(parentid) REFERENCES fake_table(fakeid))")
+
+    def do_factory(self, row):
+        return FakeRow(row)
+
+    def do_insert(self, parent, name):
+        return sql.execute("INSERT INTO fake_child (parentid, name) "
+                           "VALUES (?,?)", [ parent.rowid, name ])
 
 
 class TestTable(unittest.TestCase):
@@ -139,3 +157,33 @@ class TestModel(unittest.TestCase):
         fake.connect("items-changed", self.items_changed)
         fake.reset()
         self.assertEqual(self.changed, (0, 2, 0))
+
+
+class TestChild(unittest.TestCase):
+    def test_init(self):
+        child = FakeChild()
+
+        self.assertIsInstance(child, table.Table)
+        self.assertEqual(child.parent, "parentid")
+        self.assertEqual(child.order, "lower(name)")
+
+    def test_children(self):
+        model = FakeModel()
+        child = FakeChild()
+        parent = model.insert("Fake Parent")
+
+        self.assertEqual(child.get_n_children(parent), 0)
+
+        c = child.insert(parent, "C")
+        b = child.insert(parent, "B")
+        a = child.insert(parent, "A")
+
+        self.assertEqual(child.get_n_children(parent), 3)
+
+        self.assertEqual(child.get_child(parent, 0), a)
+        self.assertEqual(child.get_child(parent, 1), b)
+        self.assertEqual(child.get_child(parent, 2), c)
+
+        self.assertEqual(child.get_child_index(parent, a), 0)
+        self.assertEqual(child.get_child_index(parent, b), 1)
+        self.assertEqual(child.get_child_index(parent, c), 2)