Retrieve children elements from SQLite cache in list_element_children

Depends on !67 (merged)

Closes #42 (closed)

arkindex_worker/cache.py

@@ -21,6 +21,13 @@ CachedElement = namedtuple(
 )
 
 
+def convert_table_tuple(table):
+    if table == "elements":
+        return CachedElement
+    else:
+        raise NotImplementedError
+
+
 class LocalDB(object):
     def __init__(self, path):
         self.db = sqlite3.connect(path)
@@ -41,3 +48,29 @@ class LocalDB(object):
             f"INSERT INTO {table} ({columns}) VALUES ({placeholders})", values
         )
         self.db.commit()
+
+    def fetch(self, table, where=[]):
+        """
+        where parameter is a list containing 3-values tuples defining an SQL WHERE condition.
+
+        e.g: where=[("id", "LIKE", "%0000%"), ("id", "NOT LIKE", "%1111%")]
+             stands for "WHERE id LIKE '%0000%' AND id NOT LIKE '%1111%'" in SQL.
+
+        This method only supports 'AND' SQL conditions.
+        """
+
+        sql = f"SELECT * FROM {table}"
+        if where:
+            assert isinstance(where, list), "where should be a list"
+            assert all(
+                isinstance(condition, tuple) and len(condition) == 3
+                for condition in where
+            ), "where conditions should be tuples of 3 values"
+
+            sql += " WHERE "
+            sql += " AND ".join(
+                [f"{field} {operator} (?)" for field, operator, _ in where]
+            )
+        self.cursor.execute(sql, [value for _, _, value in where])
+        tuple_type = convert_table_tuple(table)
+        return [tuple_type(**dict(row)) for row in self.cursor.fetchall()]