Composite key in hibernate

It’s done using @Embeddable and @EmbeddedId annotations.

Let’s assume that we are writing an application that manages “WrokspaceTaskHistory” of various clients. Every “WrokspaceTaskHistory” has a unique “WorkspaceTaskHistoryId”.

To identify a WrokspaceTaskHistory uniquely, we need to know its WorkspaceTaskHistoryId . Check out the following workspace_task_history table that contains a composite primary key which includes both the workspace_id and task_id columns –

[xml]
CREATE TABLE `workspace_task_history` (
`workspace_id` VARCHAR(255) NOT NULL,
`task_id` VARCHAR(128) NOT NULL,
`status` VARCHAR(10) NULL,
`start_time` VARCHAR(255) NULL,
`stop_time` VARCHAR(255) NULL,
CONSTRAINT `workspaceExistsForTaskHistory`
FOREIGN KEY (`workspace_id`)
REFERENCES `demo`.`workspace` (`id`)
ON DELETE NO ACTION
ON UPDATE NO ACTION);
[/xml]
The Java code for representing the Embeddable id for the table/entity is like below
[java]
@Embeddable
public class WorkspaceTaskHistoryId implements Serializable {

@Column(name = "workspace_id") private String workspaceId;
@Column(name = "task_id") private String taskId;

public String getWorkspaceId() {
return workspaceId;
}

public void setWorkspaceId(String workspace_id) {
this.workspaceId = workspace_id;
}

public String getTaskId() {
return taskId;
}

public void setTaskId(String taskId) {
this.taskId = taskId;
}
}
[/java]

Now the usage of the @EmbeddedId to use @Embeddable class is like below
[java]
@Entity
@Table(name="workspace_task_history")
public class WorkspaceTaskHistory implements Serializable {
@EmbeddedId
WorkspaceTaskHistoryId workspaceTaskHistoryId;
@Column(name = "status") private String status;
@Column(name = "start_time") private String startTime;
@Column(name = "stop_time") private String stopTime;

public WorkspaceTaskHistory() {
}

public WorkspaceTaskHistoryId getWorkspaceTaskHistoryId() {
return workspaceTaskHistoryId;
}

public void setWorkspaceTaskHistoryId(WorkspaceTaskHistoryId workspaceTaskHistoryId) {
this.workspaceTaskHistoryId = workspaceTaskHistoryId;
}

public String getStatus() {
return status;
}

public void setStatus(String status) {
this.status = status;
}

public String getStartTime() {
return startTime;
}

public void setStartTime(String startTime) {
this.startTime = startTime;
}

public String getStopTime() {
return stopTime;
}

public void setStopTime(String stopTime) {
this.stopTime = stopTime;
}

}
[/java]

Spring Data JPA repository for the WorksspaceTaskHistory.java/ workspace_task_history.sql

[java]

@Repository
public interface WorkspaceTaskHistoryRepository extends CrudRepository<WorkspaceTaskHistory,WorkspaceTaskHistoryId>{
WorkspaceTaskHistory findByWorkspaceTaskHistoryId(WorkspaceTaskHistoryId workspaceTaskHistoryId);
}
[/java]