Delete parent row without affecting child rows in hibernate

Question

I have a problem with my code in @Manytomany hibernate relationship.

I see above issue is due to "CascadeType.ALL" on @ManyToMany relationship side. But if i remove this CascadeType.ALL in @ManyToMany. If I change this CascadeType.ALL in @ManyToMany with CascadeType.PERSIST and CascadeType.MERGE, I solve the problem. But when I add new an object will get an error. otherwise, if I change it to CascadeType.ALL, when adding new objects it works fine but it doesn't solve the problem I'm discussing. So how can I keep the rows in the Class Tag when deleting rows in Post.

public class Post {

    @Id
    @GeneratedValue
    private Long id;

    private String title;

    public Post() {}

    public Post(String title) {
        this.title = title;
    }

    @ManyToMany(cascade = {
        CascadeType.ALL
    },fetch = FetchType.EAGER)
    @JoinTable(name = "post_tag",
        joinColumns = @JoinColumn(name = "post_id"),
        inverseJoinColumns = @JoinColumn(name = "tag_id")
    )
    private List<Tag> tags = new ArrayList<>();
}

//

public class Tag {

    @Id
    @GeneratedValue
    private Long id;

    @NaturalId
    private String nameTag;

    @ManyToMany(mappedBy = "tags",fetch = FetchType.LAZY)
    private List<Post> posts = new ArrayList<>();

    public Tag() {}

    public Tag(String nameTag) {
        this.nameTag = nameTag;
    }
}

As I said above if it is CascadeType.ALL I will not be able to retain the row in Tag when I delete a row in Post when I write it is CascadeType.PERSIST and CascadeType.MERGE i get an error: object references an unsaved transient instance - save the transient instance before flushing.

And this is my input API object:

{
    "title": "System",
    "tags": [
        {
            "nameTag": "apt"
        },
        {
            "nameTag":"Worm"
        }
    ]
}

Remember that the api input works fine when I use Casecade.ALL