Minecraft wiki entry for Guardian_farming, associated text: 1. Build an iron golem-based farm without hoppers or golems (see above).
2. Dig the central canal down to bedrock.
3. Place down rails covering the canal, with powered rails every 20 blocks (recommended, although you could have up to 50 blocks spacing).
4. Place redstone blocks under every powered rail except one (near a wall), then carve out a small room near the rail without power.
5. Place a lever next to the unpowered rail, and a hopper underneath. Place 2 chests next to the hopper, make sure they are connected to the hopper. The lever should connect to the rail.
6. Place some glass overlooking the rails, place down the hopper minecart, and you are done. For more storage, place down more hoppers and chests.