实体管理器休眠持久性

Question

I have 2 entities annotated like below. When I try to remove one command line after id from the list of command lines and the application doesn't crashes but it doesn't delete the line. I'm new to java and hibernate and I have no idea what is the problem.

@Entity
public class Command {

    @OneToMany(mappedBy = "command", fetch = FetchType.EAGER, cascade = CascadeType.ALL)
    private List<CommandLine> commandLines;

and

@Entity
public class CommandLine{   

    @ManyToOne(optional = false)
    private Command command;

    public void deleteCommandLine(long id) {

        List<CommandLine> line = command.commandLines();
        for (CommandLine commandLine : line) {
            if (commandLine.getId() == id) {
                try {
                    entityManager = entityManagerFactory.createEntityManager();
                    entityManager.getTransaction().begin();
                    entityManager.remove(entityManager.merge(commandLine));
                    entityManager.getTransaction().commit();
            } catch (Exception exception) {
                exception.printStackTrace();
            }
        }
    }
}

Answer 1

像这样修改您的entityManager.remove(entityManager.merge(commandLine)行：

entityManager.remove(entityManager.contains(commandLine) ? commandLine : entityManager.merge(commandLine));

Answer 2

Entity Command is a child of Entity CommandLine so as per the data provided you need to change the Command Entity with:

@OneToMany(mappedBy = "command", orphanRemoval=true, fetch = FetchType.EAGER, cascade = CascadeType.ALL)
private List<CommandLine> commandLines;

And also you can use the delete method of Entity manager session for removing child object from the session from RAM.

entityManager.delete(commandLine);

Answer 3

you need to remove the reference to the CommandLine object in Command before removing from database. eg:

...
Command command = commandLine.getCommand();
command.getCommandLines().remove(commandLine);
entityManager.remove(entityManager.merge(commandLine));
...

A side note: doing CRUD stuff on entities should be left to Controller and service classes, don't have the objects removing themselves.