// set up
Database database = new Database(getConnection());
Table<Inventory> inventoryTable = database.getTable(Inventory.class);

// for all inventory of manufacturer 
// "manf" is name of where annotation in Inventory.java
List<Inventory> list = inventoryTable.selectAllWhere("manf", "ACME");
for (Inventory inventory: list)
{
    inventory.setQuantity(0);
}

// update
inventoryTable.updateAll(list);