Add constraints to links table columns

backend/setup_db.py

@@ -12,7 +12,14 @@ links = [
 
 # SQLite setup
 cur = con.cursor()
-cur.execute("CREATE TABLE links (url text, name text, clicks int, active int, position int)")
+cur.execute('''CREATE TABLE links (
+  url text NOT NULL, 
+  name text NOT NULL, 
+  clicks int NOT NULL, 
+  active int NOT NULL, 
+  position int NOT NULL UNIQUE,
+  UNIQUE(url, name)
+  )''')
 cur.executemany("INSERT INTO links VALUES (?,?,?,?,?)", links)
 con.commit()