如何正确实现双向休眠关系？

Question

@Entity
@Table(name = "project")
public class Project {

@Id
@Column(name = "project_id")
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;

@OneToOne
@JoinColumn(name = "idea_id", referencedColumnName = "idea_id")
@JsonIgnore
private Idea idea; .......}

和

@Entity
@Table(name = "idea")
public class Idea {

@Id
@Column(name = "idea_id")
@GeneratedValue(strategy = GenerationType.AUTO)
private int id;

@Size(max = 240)
@NotNull
private String description;

@OneToOne(cascade = CascadeType.ALL)
@JoinColumn(name = "project_id", referencedColumnName = "project_id")
private Project project; ..........}

这两个类中的休眠关系有什么问题？这是我要实现的关系示例。

这是我通过这些关系得到的实际表：

想法表：

和项目表：

如何清除项目表中idea_id列中的空值？