hsql/jdbc 等同于 JPA Detach api 是什么？它到底是做什么的？

Question

我正在使用 JDBC 将 JPA api 分离到普通 SQL，我发现很难理解 EntityManager.detach(someTask) 的概念。

我尝试使用 delete 查询进行分离，但它似乎立即从数据库中删除了整个记录。

@Entity
@Table(name = "TASK", indexes = {@Index(name = "RIO", columnList = "priority", unique = false),
@Index(name = "EXP", columnList = "expiry", unique = false), 
@Index(name = "STA", columnList = "taskStatus", unique = false),
@Index(name = "CAT", columnList = "category", unique = false),
@Index(name = "NEXTTRY", columnList = "nextTry", unique = false)})

public class TaskEntity {

@Version
private int version;

@Basic
@Column(length = Integer.MAX_VALUE, columnDefinition = "varchar(" + 
Integer.MAX_VALUE + ")")
private String taskId;

@Basic
private String category;

@ElementCollection(fetch = FetchType.EAGER)
@MapKeyColumn(name = "KEY")
@CollectionTable(name = "TASKPROPERTIES", foreignKey = @ForeignKey(
             name = "TASK_ID_FK",
             foreignKeyDefinition = "FOREIGN KEY (TASKENTITY_ID) REFERENCES TASK (ID) ON DELETE CASCADE"))

@Column(length = Integer.MAX_VALUE, columnDefinition = "varchar(" + 
Integer.MAX_VALUE + ")")
private Map<String, String> TaskProperties;

@Basic
@Column(length = Integer.MAX_VALUE, columnDefinition = "varchar(" + 
Integer.MAX_VALUE + ")")
private String destination;

@Enumerated(EnumType.STRING)
private TaskStatus taskStatus;

@Basic
private String type;

@Basic
private Long expiry;

@Basic
private Long nextTry;

@Basic
private Integer retries;

@Basic
private Integer priority;

//Setters and Getters
//Equals and HashCode

}

很难理解 detach 和 remove.So 之间的区别 HSQL/SQL 中 detach 的等效查询是什么？

Answer 1

为了理解detach，您必须首先熟悉proxy 设计模式。当您保留或获取实体时，ORM 会为您提供一个跟踪字段修改并为您提供延迟加载的代理。

当您分离一个实体时，您告诉 ORM 您不希望它再跟踪该对象实例。因此，您在分离实体实例后对其所做的任何更改都不会反映在数据库中。

换句话说，detach() 纯粹是 ORM 的一个功能，与数据库无关，这就是为什么你找不到和 SQL 等价的原因——仅仅因为有 none .

hsql/jdbc 等同于 JPA Detach api 是什么？它到底是做什么的？

what is the hsql/jdbc equivalent to JPA Detach api? what does it exactly do?

java

sql

jpa

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