jpa非管理实体 [英] jpa non managed entities

问题描述

假设我必须触发这样的查询：

Let's say I have to fire a query like this:

Select primarykey, columnname, old_value, new_value from first_audit_log;

Select primarykey, columnname, old_value, new_value from second_audit_log;

Select primarykey, columnname, old_value, new_value from third_audit_log; ...so on

audit_log 不是映射为JPA enity到任何类，我严格不能创建 n n 的数量 * _ audit_logs 。

audit_log is not mapped as JPA enity to any class and I strictly can't create n number of classes for n number of *_audit_logs.

使用本机查询功能，我如何才能将其映射到泛型类？尝试选择新功能，但不确定...因此，任何帮助都表示赞赏。

Using native query feature, how best I can map this to a generic class? Trying to SELECT NEW feature, but not sure... Hence any help is appreciated.

推荐答案

由于审计日志表共享在相同的列中，您可以创建一个统一这些表并将单个Java类映射到该视图的视图。我相信你可以，因为你不需要写更新，我想。

Since your audit logs tables share the same columns, you can create a view that "unifies" those tables and map a single Java class to that view. I believe you can, since you don't need to write updates, I guess.

作为替代方案，使用本机查询将是一个不错的选择。

As an alternative, using native queries would be a good choice.

编辑：

1）如果审核日志已经如果您不想为每个视图创建映射Java类，则可以基于其他视图创建视图。只记得添加一个值为 1 的虚拟列，如果该行来自第一个审核日志， 2 如果它来自第二个，依此类推，那么你可以将它们分开。

1) If your audit logs are already views, you can create a view based on other views, if you don't want to create a mapping Java class for each of them. Just remember to add a dummy column that has value 1 if the row comes from the "first" audit log, 2 if it comes from the second, and so on, so you can set them apart.

2）为了使用本机查询，假设您的持久性提供程序是Hibernate，那么可以这样做：

2) In order to use native queries, assuming your persistence provider is Hibernate, you can do like in this example:

EntityManagerFactory emf = Persistence.createEntityManagerFactory("test");
EntityManager em = emf.createEntityManager();

Session sess = em.unwrap(Session.class); // <-- Use Hibernate-specific features
SQLQuery query = sess.createSQLQuery(
   "SELECT AVG(age) AS averageAge, AVG(salary) as averageSalary FROM persons");

query.setResultTransformer(Transformers.aliasToBean(MyResult.class));
MyResult result = (MyResult) query.list().get(0);

其中 MyResult 声明如下：

public class MyResult {

    private BigDecimal averageAge;
    private BigDecimal averageSalary;

    public BigDecimal getAverageAge() {
        return averageAge;
    }
    public void setAverageAge(BigDecimal averageAge) {
        this.averageAge = averageAge;
    }
    public BigDecimal getAverageSalary() {
        return averageSalary;
    }
    public void setAverageSalary(BigDecimal averageSalary) {
        this.averageSalary = averageSalary;
    }

}

和人表是这样的（MySQL语法）：

and the persons table is like this (MySQL syntax):

CREATE TABLE `persons` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `firstname` varchar(255) NOT NULL,
  `lastname` varchar(255) NOT NULL,
  `age` int(11) NOT NULL,
  `salary` int(11) NOT NULL,
  PRIMARY KEY (`id`)
);

您可以根据需要轻松调整此示例，只需替换人和 MyResult 。

You can easily adapt this example to your needs, just replace persons and MyResult with what you want.

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