如何在 JPA 域模型中实现状态设计模式
我想在 JPA 中实现状态设计模式。我目前这样做的方式在这个 博客中概述发布。
作者使用包含所有可用状态实现的枚举,而不是创建抽象类/接口来进行状态抽象并为每个状态编写实现。我发现这种方法非常有用,因为枚举可以在 JPA 中轻松序列化,并且您可以存储对象的当前状态,而无需额外的工作。我还将状态接口和所有状态类嵌套到枚举中,使它们成为私有的,因为它们是特定于实现的并且不应该对任何客户端可见。这是枚举的代码示例:
public enum State {
STATE_A(new StateA()),
STATE_B(new StateB());
private final StateTransition state;
private State(StateTransition state) {
this.state = state;
}
void transitionA(Context ctx) {
state.transitionA(ctx);
}
void transitionB(Context ctx) {
state.transitionB(ctx);
}
private interface StateTransition {
void transitionA(Context ctx);
void transitionB(Context ctx);
}
private static class StateA implements StateTransition {
@Override
public void transitionA(Context ctx) {
// do something
ctx.setState(STATE_B);
}
@Override
public void transitionB(Context ctx) {
// do something
ctx.setState(STATE_A);
}
}
private static class StateB implements StateTransition {
@Override
public void transitionA(Context ctx) {
throw new IllegalStateException("transition not allowed");
}
@Override
public void transitionB(Context ctx) {
// do something
ctx.setState(STATE_A);
}
}
}
我想与您分享并了解您的想法。你觉得这有用吗?您将如何在 JPA 域模型中实现状态设计模式?
I want to implement the state design pattern in JPA. The way I am currently doing this is outlined in this blog post.
The author uses an enum containing all available state implementations instead of creating abstract class/interface for state abstraction and writing implementation for each state. I find this approach very useful, since enums can be easily serialized in JPA and you can store the current state of your object without additional effort. I also nested the state interface and all state classes into the enum making them private, since they are implementation specific and should not be visible to any client. Here's a code example of the enum:
public enum State {
STATE_A(new StateA()),
STATE_B(new StateB());
private final StateTransition state;
private State(StateTransition state) {
this.state = state;
}
void transitionA(Context ctx) {
state.transitionA(ctx);
}
void transitionB(Context ctx) {
state.transitionB(ctx);
}
private interface StateTransition {
void transitionA(Context ctx);
void transitionB(Context ctx);
}
private static class StateA implements StateTransition {
@Override
public void transitionA(Context ctx) {
// do something
ctx.setState(STATE_B);
}
@Override
public void transitionB(Context ctx) {
// do something
ctx.setState(STATE_A);
}
}
private static class StateB implements StateTransition {
@Override
public void transitionA(Context ctx) {
throw new IllegalStateException("transition not allowed");
}
@Override
public void transitionB(Context ctx) {
// do something
ctx.setState(STATE_A);
}
}
}
I'd like to and share this with you and get your thoughts on it. Do you find this useful? How would you implement the state design pattern in a JPA domain model?
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作为推论,这种 AspectJ 模式与特定于常量的 Enum 类相结合也是有用的。我在这里不展示 Spring 集成,因为这仅关注 AspectJ。但我想我们也可以将 Spring 与 AspectJ 一起使用。
还有一点是,面向对象模式对于这个用例来说非常强大。我展示此模式只是因为问题指向博客文章,其中包含 Spring 和 AspectJ 示例的链接。
我还需要在 JPA 中使用良好的 OO 模式。
测试代码:
As a corollary this AspectJ pattern combined with constant-specific Enum classes is also useful. I am not showing Spring integration here as this focuses only on AspectJ. But I guess we can use Spring with AspectJ too.
One more point is that OO patterns can be powerful for this usecase. I show this pattern only because the question points to the blog post which has a link to a Spring and AspectJ example.
And I also have a need to use good OO patterns with JPA.
Test code :
嗯,这是一个老问题,但是为了那些可能搜索档案的人 - 我使用了带有枚举(而不是字符串)的 spring 状态机。
关于处理转换,有一些注释允许在转换发生时调用您的函数。
1.1.0.RELEASE 提供了一种默认机制,通过 持久化 StateMachineContext,以及使用 坚持配方。
现在参考 JPA - 可以让实体监听器在 postload< 上初始化状态机/a> (@Postload),我认为这不是一条好路。
Well it's an old question, but for the sake of those who might search archives - I have used spring state machine with enums (instead Strings).
Regarding handling transitions, there are annotations that allow your functions to be called when transition happens.
1.1.0.RELEASE gives a default mechanism to persist a state by persisting StateMachineContext, and an alternative using persist recipe.
Now refering to JPA - it's possible to have Entity Listener that will initialize statemachine on postload (@Postload), I think it's not good path to go.