java - Hibernate Lazy 集合的正确初始化

Question

我是否正确初始化了惰性集合？我的主要目标是进行数据库查询并初始化惰性集合，以便它可以由没有数据库 session 的方法使用。

我当前的方法有效，但它似乎多次查询数据库。谁能确认这是正确的或告诉我正确的方法。

服务类方法

    public void testing() {
    
        try {
            List<User> users = test();
    
            for (User user : users) {
                System.out.println(user);
                Set<UserGroupMapping> userGroupMapping   = user.getUserGroupMappings();
    
                for (UserGroupMapping userGroupMapping : userGroupMapping) {
                    System.out.println(userGroupMapping);
                }
    
            }
    
        } catch (Exception e) {
            e.printStackTrace();
        }
    
    }

@Transactional(value = "transactionManager", propagation = Propagation.REQUIRED, isolation = Isolation.DEFAULT, readOnly = true)
private List<User> test() {
    return  dao.findUsers();    
}

Dao类方法

@Transactional(value = "transactionManager", propagation = Propagation.MANDATORY, isolation = Isolation.DEFAULT, readOnly = true)
public List<User> findUsers() {
    Criteria criteria = getCesSession().createCriteria(User.class);
    
            criteria.setFetchMode("userGroupMappings", FetchMode.SELECT);
    
            @SuppressWarnings("unchecked")
            List<User> list = (List<User>) criteriaList(criteria);
    
            for (User user : list) {
                Set<UserGroupMapping> b = user.getUserGroupMappings();
    
                Hibernate.initialize(b);
    
                for (UserGroupMapping userGroupMapping : b) {
                    Hibernate.initialize(userGroupMapping.getGroup());
                }
    
            }
    
            return list;
        }

用户实体

@Entity
@Table(name = "[User]", schema = "dbo", catalog = "Test", uniqueConstraints = @UniqueConstraint(columnNames = "userName"))
public class User extends DatabaseObject {

    private Long userId;
    private Set<UserGroupMapping> userGroupMappings = new HashSet<UserGroupMapping>(
            0);

    @Id
    @Column(name = "userId", unique = true, nullable = false)
    public Long getUserId() {
        return this.userId;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "user")
    public Set<UserGroupMapping> getUserGroupMappings() {
        return this.userGroupMappings;
    }

群组实体

@Entity
@Table(name = "[Group]", schema = "dbo", catalog = "Test", uniqueConstraints = @UniqueConstraint(columnNames = "name"))
public class Group extends DatabaseObject {

    private Long groupId;
    private Set<GroupRoleMapping> groupRoleMappings = new HashSet<GroupRoleMapping>(0);
    private Set<UserGroupMapping> userGroupMappings = new HashSet<UserGroupMapping>(0);

    @Id
    @Column(name = "groupId", unique = true, nullable = false)
    public Long getGroupId() {
        return this.groupId;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "group")
    public Set<GroupRoleMapping> getGroupRoleMappings() {
        return this.groupRoleMappings;
    }

    @OneToMany(fetch = FetchType.LAZY, mappedBy = "group")
    public Set<UserGroupMapping> getUserGroupMappings() {
        return this.userGroupMappings;
    }

UserGroupMapping 实体

@Entity
@Table(name = "UserGroupMapping", schema = "dbo", catalog = "Test", uniqueConstraints = @UniqueConstraint(columnNames = "userId"))
public class UserGroupMapping extends DatabaseObject {

    private Long userGroupMappingId;
    private Group group;
    private User user;

    @Id
    @Column(name = "userGroupMappingId", unique = true, nullable = false)
    public Long getUserGroupMappingId() {
        return this.userGroupMappingId;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "groupId", nullable = false)
    public Group getGroup() {
        return this.group;
    }

    @ManyToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "userId", unique = true, nullable = false)
    public User getUser() {
        return this.user;
    }
}

日志

DEBUG: 15:19:22.251 - 
    /* criteria query */ select
        this_.userId as userId1_17_0_,
        this_.createdBy as createdB2_17_0_,
        this_.dateCreated as dateCrea3_17_0_,
        this_.dateUpdated as dateUpda4_17_0_,
        this_.name as name5_17_0_,
        this_.password as password6_17_0_,
        this_.updatedBy as updatedB7_17_0_,
        this_.userName as userName8_17_0_ 
    from
        CES_SIT.dbo.[User] this_
Hibernate: 
    /* criteria query */ select
        this_.userId as userId1_17_0_,
        this_.createdBy as createdB2_17_0_,
        this_.dateCreated as dateCrea3_17_0_,
        this_.dateUpdated as dateUpda4_17_0_,
        this_.name as name5_17_0_,
        this_.password as password6_17_0_,
        this_.updatedBy as updatedB7_17_0_,
        this_.userName as userName8_17_0_ 
    from
        CES_SIT.dbo.[User] this_




    DEBUG: 15:19:39.159 - 
        select
            usergroupm0_.userId as userId7_17_0_,
            usergroupm0_.userGroupMappingId as userGrou1_15_0_,
            usergroupm0_.userGroupMappingId as userGrou1_15_1_,
            usergroupm0_.createdBy as createdB2_15_1_,
            usergroupm0_.dateCreated as dateCrea3_15_1_,
            usergroupm0_.dateUpdated as dateUpda4_15_1_,
            usergroupm0_.groupId as groupId6_15_1_,
            usergroupm0_.updatedBy as updatedB5_15_1_,
            usergroupm0_.userId as userId7_15_1_ 
        from
            CES_SIT.dbo.UserGroupMapping usergroupm0_ 
        where
            usergroupm0_.userId=?
    Hibernate: 
        select
            usergroupm0_.userId as userId7_17_0_,
            usergroupm0_.userGroupMappingId as userGrou1_15_0_,
            usergroupm0_.userGroupMappingId as userGrou1_15_1_,
            usergroupm0_.createdBy as createdB2_15_1_,
            usergroupm0_.dateCreated as dateCrea3_15_1_,
            usergroupm0_.dateUpdated as dateUpda4_15_1_,
            usergroupm0_.groupId as groupId6_15_1_,
            usergroupm0_.updatedBy as updatedB5_15_1_,
            usergroupm0_.userId as userId7_15_1_ 
        from
            CES_SIT.dbo.UserGroupMapping usergroupm0_ 
        where
            usergroupm0_.userId=?



    DEBUG: 15:19:39.176 - Preparing collection intializer : [com.bdo.ces.entities.User.userGroupMappings#1]
    DEBUG: 15:19:39.176 - Starting ResultSet row #0
    DEBUG: 15:19:39.177 - Found row of collection: [com.bdo.ces.entities.User.userGroupMappings#1]
    DEBUG: 15:19:39.177 - Resolving associations for [com.bdo.ces.entities.UserGroupMapping#1]
    DEBUG: 15:19:39.177 - Done materializing entity [com.bdo.ces.entities.UserGroupMapping#1]
    DEBUG: 15:19:39.177 - 1 collections were found in result set for role: com.bdo.ces.entities.User.userGroupMappings
    DEBUG: 15:19:39.177 - Collection fully initialized: [com.bdo.ces.entities.User.userGroupMappings#1]
    DEBUG: 15:19:39.177 - 1 collections initialized for role: com.bdo.ces.entities.User.userGroupMappings
    DEBUG: 15:19:39.177 - Done loading collection
    DEBUG: 15:19:39.177 - Initializing proxy: [com.bdo.ces.entities.Group#1]
    DEBUG: 15:19:39.177 - 
        select
            group0_.groupId as groupId1_16_0_,
            group0_.createdBy as createdB2_16_0_,
            group0_.dateCreated as dateCrea3_16_0_,
            group0_.dateUpdated as dateUpda4_16_0_,
            group0_.description as descript5_16_0_,
            group0_.name as name6_16_0_,
            group0_.updatedBy as updatedB7_16_0_,
            group0_.visible as visible8_16_0_ 
        from
            CES_SIT.dbo.[
        Group] group0_ where
            group0_.groupId=?
    Hibernate: 
        select
            group0_.groupId as groupId1_16_0_,
            group0_.createdBy as createdB2_16_0_,
            group0_.dateCreated as dateCrea3_16_0_,
            group0_.dateUpdated as dateUpda4_16_0_,
            group0_.description as descript5_16_0_,
            group0_.name as name6_16_0_,
            group0_.updatedBy as updatedB7_16_0_,
            group0_.visible as visible8_16_0_ 
        from
            CES_SIT.dbo.[
        Group] group0_ where
            group0_.groupId=?

使用 K.C 进行测试==================================

Dao类方法

@Transactional(value = "transactionManager", propagation = Propagation.MANDATORY, isolation = Isolation.DEFAULT, readOnly = true)
        public List<User> findUsers() {
    Criteria criteria = getCesSession().createCriteria(User.class);
    
            criteria.setFetchMode("userGroupMappings", FetchMode.JOIN);
    
            criteria.createAlias("userGroupMappings", "userGroupMappings",
                    JoinType.LEFT_OUTER_JOIN);
    
            @SuppressWarnings("unchecked")
            List<User> list = (List<User>) criteriaList(criteria);
    
            Hibernate.initialize(list);
    
            for (User user : list) {
                Set<UserGroupMapping> b = user.getUserGroupMappings();
                
                Hibernate.initialize(b);
    
                for (UserGroupMapping userGroupMapping : b) {
                    Hibernate.initialize(userGroupMapping.getGroup());
                }
    
            }
    
            return list; 
    
                }

日志

DEBUG: 17:40:19.989 - 
    /* criteria query */ select
        this_.userId as userId1_17_1_,
        this_.createdBy as createdB2_17_1_,
        this_.dateCreated as dateCrea3_17_1_,
        this_.dateUpdated as dateUpda4_17_1_,
        this_.name as name5_17_1_,
        this_.password as password6_17_1_,
        this_.updatedBy as updatedB7_17_1_,
        this_.userName as userName8_17_1_,
        usergroupm1_.userId as userId7_17_3_,
        usergroupm1_.userGroupMappingId as userGrou1_15_3_,
        usergroupm1_.userGroupMappingId as userGrou1_15_0_,
        usergroupm1_.createdBy as createdB2_15_0_,
        usergroupm1_.dateCreated as dateCrea3_15_0_,
        usergroupm1_.dateUpdated as dateUpda4_15_0_,
        usergroupm1_.groupId as groupId6_15_0_,
        usergroupm1_.updatedBy as updatedB5_15_0_,
        usergroupm1_.userId as userId7_15_0_ 
    from
        CES_SIT.dbo.[User] this_ 
    left outer join
        CES_SIT.dbo.UserGroupMapping usergroupm1_ 
            on this_.userId=usergroupm1_.userId
Hibernate: 
    /* criteria query */ select
        this_.userId as userId1_17_1_,
        this_.createdBy as createdB2_17_1_,
        this_.dateCreated as dateCrea3_17_1_,
        this_.dateUpdated as dateUpda4_17_1_,
        this_.name as name5_17_1_,
        this_.password as password6_17_1_,
        this_.updatedBy as updatedB7_17_1_,
        this_.userName as userName8_17_1_,
        usergroupm1_.userId as userId7_17_3_,
        usergroupm1_.userGroupMappingId as userGrou1_15_3_,
        usergroupm1_.userGroupMappingId as userGrou1_15_0_,
        usergroupm1_.createdBy as createdB2_15_0_,
        usergroupm1_.dateCreated as dateCrea3_15_0_,
        usergroupm1_.dateUpdated as dateUpda4_15_0_,
        usergroupm1_.groupId as groupId6_15_0_,
        usergroupm1_.updatedBy as updatedB5_15_0_,
        usergroupm1_.userId as userId7_15_0_ 
    from
        CES_SIT.dbo.[User] this_ 
    left outer join
        CES_SIT.dbo.UserGroupMapping usergroupm1_ 
            on this_.userId=usergroupm1_.userId


    select
        group0_.groupId as groupId1_16_0_,
        group0_.createdBy as createdB2_16_0_,
        group0_.dateCreated as dateCrea3_16_0_,
        group0_.dateUpdated as dateUpda4_16_0_,
        group0_.description as descript5_16_0_,
        group0_.name as name6_16_0_,
        group0_.updatedBy as updatedB7_16_0_,
        group0_.visible as visible8_16_0_ 
    from
        CES_SIT.dbo.[
    Group] group0_ where
        group0_.groupId=?
Hibernate: 
    select
        group0_.groupId as groupId1_16_0_,
        group0_.createdBy as createdB2_16_0_,
        group0_.dateCreated as dateCrea3_16_0_,
        group0_.dateUpdated as dateUpda4_16_0_,
        group0_.description as descript5_16_0_,
        group0_.name as name6_16_0_,
        group0_.updatedBy as updatedB7_16_0_,
        group0_.visible as visible8_16_0_ 
    from
        CES_SIT.dbo.[
    Group] group0_ where
        group0_.groupId=?

DEBUG: 17:40:38.189 - 
    select
        group0_.groupId as groupId1_16_0_,
        group0_.createdBy as createdB2_16_0_,
        group0_.dateCreated as dateCrea3_16_0_,
        group0_.dateUpdated as dateUpda4_16_0_,
        group0_.description as descript5_16_0_,
        group0_.name as name6_16_0_,
        group0_.updatedBy as updatedB7_16_0_,
        group0_.visible as visible8_16_0_ 
    from
        CES_SIT.dbo.[
    Group] group0_ where
        group0_.groupId=?
Hibernate: 
    select
        group0_.groupId as groupId1_16_0_,
        group0_.createdBy as createdB2_16_0_,
        group0_.dateCreated as dateCrea3_16_0_,
        group0_.dateUpdated as dateUpda4_16_0_,
        group0_.description as descript5_16_0_,
        group0_.name as name6_16_0_,
        group0_.updatedBy as updatedB7_16_0_,
        group0_.visible as visible8_16_0_ 
    from
        CES_SIT.dbo.[
    Group] group0_ where
        group0_.groupId=?
DEBUG: 17:40:38.197 - Starting ResultSet row #0

最终==============================

使用这段代码让它工作我仍然不确定这是否是最好的方法，但它只在一个查询中加载惰性集合。我还在 [userGroupMappings.group] 中加入了惰性对象以使其正常工作。

我以为 Hibernate.initialize() 会为我做到这一点，但事实并非如此。

**Dao Class Method**


    @Transactional(value = "transactionManager", propagation = Propagation.MANDATORY, isolation = Isolation.DEFAULT, readOnly = true)
            public List<User> findUsers() {
        Criteria criteria = getCesSession().createCriteria(User.class);
                            
                criteria.createCriteria("userGroupMappings", "userGroupMappings",
                        JoinType.LEFT_OUTER_JOIN);
                criteria.createCriteria("userGroupMappings.group", "userGroupMappings.group",
                        JoinType.LEFT_OUTER_JOIN);
        
                @SuppressWarnings("unchecked")
                List<User> list = (List<User>) criteriaList(criteria);
        
                
       
                return list; 
        
                    }

Answer 1

由于 User - UserGroupMapping 1 - n 映射，您有 n + 1 选择问题，如here所述。这就是为什么您有这么多疑问。

您可以通过在 UserGroupMapping 上执行左外连接来避免这种情况。