ActiveJPA 介绍
ActiveJPA基于JPA，提供了Martin Fowler所提出的活动记录模式（Active Record
pattern）的Java实现。借助于ActiveJPA，模型本身会作为DAO并与数据库交互，这样就不需要额外的代码作为数据访问层了。
ActiveJPA使用到了JPA规范，因此所有JPA的ORM实现（Hibernate、EclipseLink、OpenJPA等）都可以与ActiveJPA协同使用。
示例代码：
// Get order by id
Order order = Order.findById(12345L);
// Get all orders for a customer that are shipped
List<Order> orders = Order.where("customer_email", "[email protected]", "status", "shipped");
// Get all orders for the product category 'books' and paginate it
Filter filter = new Filter();
filter.setPageNo(1);
filter.setPerPage(25);
filter.addCondition(new Condition("orderItems.product.category", Operator.eq, "books");
List<Order> orders = Order.where(filter);
// Count of orders matching the filter
Long count = Order.count(filter);
// Get the first order matching the filter
Long count = Order.first("customer_email", "[email protected]", "status", "shipped");
// Get the unique order matching the conditions
Long count = Order.one("customer_email", "[email protected]", "status", "shipped");
// Dump everything
List<Order> orders = Order.all();
// Delete all orders matching the filter
Long count = Order.deleteall(filter);
// Check if order exists with the given identifier
boolean exists = Order.exists(1234L);
// Save order
order.setBillingAmount(1000.0);
order.persist();
// Delete order
order.delete();
// Update attributes
Map<String, Object> attributes = new HashMap<String, Object>();
attributes.put("billingAmount", 1000.0);
order.updateAttributes(attributes);
// Find order item by id within an order
order.collections("order_items").findById(123L);
// Search order items by filter with an order
order.collections("order_items").findById(filter);
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