Sorry for my poor English.
There are 3 objects: PostTable, Post and Category.
Post and Category both extends PostTable . PostTable represents the data table named "cp_table". The "type" field is the DiscriminatorColumn of table, data type is integer.
The Category entity's DiscriminatorValue is "1", the Post's is "2".
The code outlines of them as below:

@Entity
@Table(name = "cp_post")
@Inheritance(strategy = InheritanceType.SINGLE_TABLE)
@DiscriminatorColumn(name = "type", discriminatorType = DiscriminatorType.INTEGER)
public class PostTable {

        // ignore getters and setters
        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        protected Integer id;
        protected String title;
        protected String alias;
        protected String keyword;
        protected String summary;
        protected String author;
        protected String source;
        protected Date updateTime;
        protected String content;
        protected Integer hits;
        protected Integer postOrder;
        @ManyToOne(fetch = FetchType.LAZY)
        @JoinColumn(nullable = false)
        protected User user;
        protected Date addTime;
        protected Integer status;
        protected String image;    
}


@Entity
@DiscriminatorValue("1")
public class Category extends PostTable {

    // ignore getters and setters
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn
    protected Category category;

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "category")
    @OrderBy("postOrder ASC")
    protected List<Category> children;
}



@Entity
@DiscriminatorValue("2")
public class Post extends PostTable {

    // ignore getters and setters
    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn
    protected Category category;
 
}

However, when I invoke Category Entity's getChildren() method to gain the associated Collection of Category, I found that the collection contains the Post entity ( which's type = "2") unexpectedly !

The java code as blow:

Category category = hibernateDao.get(Category.class, 7);
List<Category> children = category.getChildren();
for (Category child : children) {
    System.out.println(child.getId());
}

The corresponding SQL statement as blow:
"
SELECT
children0_.category_id AS categor17_38_1_,
children0_.id AS id2_38_1_,
children0_.id AS id2_38_0_,
children0_.add_time AS add_time3_38_0_,
children0_.alias AS alias4_38_0_,
children0_.author AS author5_38_0_,
children0_.content AS content6_38_0_,
children0_.hits AS hits7_38_0_,
children0_.image AS image8_38_0_,
children0_.keyword AS keyword9_38_0_,
children0_.post_order AS post_or10_38_0_,
children0_.source AS source11_38_0_,
children0_. STATUS AS status12_38_0_,
children0_.summary AS summary13_38_0_,
children0_.title AS title14_38_0_,
children0_.update_time AS update_15_38_0_,
children0_.user_id AS user_id16_38_0_,
children0_.category_id AS categor17_38_0_
FROM
cp_post children0_
WHERE
children0_.category_id =?
ORDER BY
children0_.post_order ASC
"

However, the expected query should add type restriction. e.g. " AND children0_.type = 1" .
Because the definition of Category entity is "type = 1", it should be treated strictly in anywhere.

Additionally. the Hibernate version I'm using is 5.2.6 Final. I've no enough time to test for each version.
Best wishes.