Question

我是学生，是Stack Overflow，spring-boot和hibernate stack的新手。

问题：根据类别ID返回问题列表。

由于我的模型实体类在下面，我没有categoryId（外键）的属性，因为这是通过关系注释自动生成的。

我似乎能够返回所有问题的列表，没有过滤级别，但也想要一个根据类别ID（外键）返回问题的方法。

非常感谢任何帮助，谢谢！

使用hibernate 5.2

categoryModel

@Entity
public class Category {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

@NotNull
@Size(min = 3, max = 20)
private String name;

@NotNull
@Pattern(regexp = "#[0-9a-fA-F]{6}")
private String colorCode;

@OneToMany(mappedBy = "category")
private List<Question> questions = new ArrayList<>();

public Category(){}

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public List<Question> getQuestions() {
    return questions;
}

public String getColorCode() {
    return colorCode;
}

public void setColorCode(String colorCode) {
    this.colorCode = colorCode;
}

questionModel

@Entity
public class Question {

@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;

private String name;

@ManyToOne
private Category category;

private LocalDateTime dateCreated = LocalDateTime.now();

public Question(){}

public String getTimeSinceUploaded() {
    String unit = "";
    LocalDateTime now = LocalDateTime.now();
    long diff;
    if((diff = ChronoUnit.SECONDS.between(dateCreated,now)) < 60){
        unit = "secs";
    } else if ((diff = ChronoUnit.MINUTES.between(dateCreated,now)) < 60) {
        unit = "mins";
    } else if ((diff = ChronoUnit.HOURS.between(dateCreated,now)) < 24) {
        unit = "hours";
    } else if ((diff = ChronoUnit.DAYS.between(dateCreated,now)) < 30) {
        unit = "days";
    } else if ((diff = ChronoUnit.MONTHS.between(dateCreated,now)) < 12) {
        unit = "months";
    } else{
        diff = ChronoUnit.YEARS.between(dateCreated,now);
    }
    return String.format("%d %s",diff,unit);
}

public Long getId() {
    return id;
}

public void setId(Long id) {
    this.id = id;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public Category getCategory() {
    return category;
}

public void setCategory(Category category) {
    this.category = category;
}

public LocalDateTime getDateCreated() {
    return dateCreated;
}

public void setDateCreated(LocalDateTime dateCreated) {
    this.dateCreated = dateCreated;
}

}

问题DAO

@Repository
public class QuestionDaoImpl implements IQuestionDao {

@Autowired
private SessionFactory sessionFactory;


/**
 * Returns a list of all the questions - michael
 */
@Override
public List<Question> findAll() {

    Session session = sessionFactory.openSession();
    // Create CriteriaBuilder
    CriteriaBuilder builder = session.getCriteriaBuilder();
    // Create CriteriaQuery
    CriteriaQuery<Question> criteria = builder.createQuery(Question.class);
    // Specify criteria root
    criteria.from(Question.class);
    // Execute query
    List<Question> questions = session.createQuery(criteria).getResultList();
    session.close();

    return questions;
}

/**
 * Returns A question by using the id - michael
 */
@Override
public Question findById(Long id) {
    Session session = sessionFactory.openSession();
    Question question = session.get(Question.class, id);
    session.close();
    return question;
}

/**
 * TODO: ml- Finds a list of questions according to the category_id
 */
@Override
public List<Question> findByCategoryId(Long categoryId){

    // This is a issue i a have here

return null;
}

Answer 1

试试这个，你必须传递你创建的对象问题实体的类别对象bcz，

@Override
public List<Question> findByCategoryId(Long categoryId){

     Session session = sessionFactory.openSession();
    final Criteria cr = session.createCriteria(Question.class);
    cr.add(Restrictions.eq("category", category));

    return cr.list();
}

如果有任何问题，请告诉我。

Answer 2

您的Dao是否扩展了crudrepository或JpaRepository？

通过category_id查找Hibernate，Spring

2 个答案: