在一个 Table 上休眠两个 ManyToOne 关系，第一个获取 Eager，第二个加载 LAZY
Hibernate two ManyToOne relations on one Table, the first gets Eager and the second LAZY loaded
我有以下实体，一个 item 最多可以有两个类别，一个主要的和一个次要的。
这两个类别都使用 JoinColumnsOrFormulas 映射 ManyToOne 到 category table。
第一个按预期获取 EAGER，但第二个未出现在 SQL 语句中并延迟加载。
这种延迟加载会导致经典的 n+1 问题。
这是我的项目实体，其中包含应该加入的两个类别实体：
@Entity
@Table(name = "item", schema = "public", catalog = "Whosebug_question")
@DynamicUpdate
public class Item extends WhosebugQuestionEntity {
@Id
@Column(name = "id")
protected Long id;
@Column(name = "site")
private String site;
@ManyToOne
@JoinColumnsOrFormulas({
@JoinColumnOrFormula(formula = @JoinFormula(value = "site", referencedColumnName = "site")),
@JoinColumnOrFormula(formula = @JoinFormula(value = "primary_category_id", referencedColumnName = "category_id"))
})
private Category primaryCategory;
@Column(name = "primary_category_id")
private Long primaryCategoryId;
@ManyToOne
@JoinColumnsOrFormulas({
@JoinColumnOrFormula(formula = @JoinFormula(value = "site", referencedColumnName = "site")),
@JoinColumnOrFormula(formula = @JoinFormula(value = "secondary_category_id", referencedColumnName = "category_id"))
})
private Category secondaryCategory;
@Column(name = "secondary_category_id")
private Long secondaryCategoryId;
}
这是类别实体：
@Entity
@Table(name = "category", schema = "public", catalog = "Whosebug_question")
public class Category extends WhosebugQuestionEntity {
@Column(name = "category_id")
private Long categoryId;
@Column(name = "name")
private String name;
@Column(name = "site")
private String site;
}
生成的查询仅包含主要类别：
SELECT this_.id AS id1_9_9_,
this_.inserted AS inserted2_9_9_,
this_.updated AS updated3_9_9_,
this_.primary_category_id AS formula174_9_,
this_.secondary_category_id AS formula176_9_,
category2_.id AS id1_0_0_,
category2_.inserted AS inserted2_0_0_,
category2_.updated AS updated3_0_0_,
category2_.name AS name7_0_0_
FROM public.item this_
LEFT OUTER JOIN public.category category2_ ON this_.site=category2_.site
AND this_.primary_category_id=category2_.category_id
WHERE True;
因此次要类别懒惰加入：
SELECT category0_.id AS id1_0_0_,
category0_.inserted AS inserted2_0_0_,
category0_.updated AS updated3_0_0_,
category0_.name AS name4_0_0_,
category0_.site AS site5_0_0_
FROM public.category category0_
WHERE category0_.site=?
AND category0_.category_id=?;
为什么Hibernate加入secondary category lazy，注解好像是一样的
我使用的hibernate版本是5.0.10.Final.
这是基础实体的样子：
@MappedSuperclass
abstract public class WhosebugQuestionEntity implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", unique = true, insertable = true, updatable = false, nullable = false)
protected Long id;
@Type(type="LocalDateTime")
@Column(name = "created", nullable = false, insertable = true, updatable = false)
protected LocalDateTime created;
@Type(type="LocalDateTime")
@Column(name = "refreshed", nullable = false, insertable = true, updatable = true)
protected LocalDateTime refreshed;
@PreUpdate
protected void onUpdate() {
refreshed = now();
}
@PrePersist
protected void onCreate() {
created = refreshed = now();
}
}
这里有一个例子"query"，正如我所说的，我正在使用hibernate criteria和HQL，这两种方法都会出现问题。
session
.createCriteria(Item.class)
.add(eq("id", id))
.uniqueResult();
使用标准 JPA 注释，它看起来像这样（已更新）：
@ManyToOne
@JoinColumns({
@JoinColumn(name="site", referencedColumnName="site", insertable = false, updatable = false),
@JoinColumn(name="primary_category_id", referencedColumnName="category_id", insertable = false, updatable = false)
})
private Category primaryCategory;
@ManyToOne
@JoinColumns({
@JoinColumn(name="site", referencedColumnName="site", insertable = false, updatable = false),
@JoinColumn(name="secondary_category_id", referencedColumnName="category_id", insertable = false, updatable = false)
})
private Category secondaryCategory;
更新： 我发现第二个 select 语句仅在您通过复合键使用 join 时生成：Hibernate 尝试解析关联{site=site, id=null} 使用 TwoPhaseLoad。但是如果你写
@ManyToOne
@JoinColumn(name="secondary_category_id")
private Category secondaryCategory;
且secondary_category_id为null则生成唯一的select语句，secondaryCategory值为null。也许它会以某种方式帮助你。例如，您可以在构建条件时对 site 字段添加约束：
Category c = (Category) session.createCriteria(Category.class)
.add(Restrictions.eq("id", 1L)) // for example
// here you define additional restriction on site field
.createAlias("secondaryCategory", "sc", JoinType.LEFT_OUTER_JOIN, Restrictions.sqlRestriction("this_.site = {alias}.site"))
.uniqueResult();
尝试以下解决方案：
@Entity
@Table(name = "item", schema = "public", catalog = "Whosebug_question")
@DynamicUpdate
public class Item {
@ManyToOne
@JoinColumn(name="site")
private Category primaryCategory;
@ManyToOne
@JoinColumn(name="site")
private Category secondaryCategory;
}
@Entity
@Table(name = "category", schema = "public", catalog = "Whosebug_question")
public class Category {
@OneToMany(targetEntity=Item.class, mappedBy="primaryCategory", cascade=CascadeType.ALL)
private List<Item> primaryCategoryList;
@OneToMany(targetEntity=Item.class, mappedBy="secondaryCategory", cascade=CascadeType.ALL)
private List<Item> secondaryCategoryList;
}
我使用您的 类 和以下查询代码（使用 JPA 条件查询而不是本机 Hibernate）进行了快速测试
CriteriaQuery<Item> cq = em.getCriteriaBuilder().createQuery(Item.class);
EntityGraph<Item> entityGraph = em.createEntityGraph(Item.class);
entityGraph.addSubgraph("primaryCategory", Category.class);
entityGraph.addSubgraph("secondaryCategory", Category.class);
List<Item> items = em.createQuery(cq.select(cq.from(Item.class)))
.setHint("javax.persistence.loadgraph", entityGraph)
.getResultList();
导致生成以下 SQL（为了便于阅读而格式化）：
select item0_.id as id1_1_0_,
category1_.id as id1_0_1_,
category2_.id as id1_0_2_,
item0_.site as site4_1_0_,
item0_.primary_category_id as primary_2_1_0_,
item0_.secondary_category_id as secondar3_1_0_,
category1_.category_id as category2_0_1_,
category1_.name as name3_0_1_,
category1_.site as site4_0_1_,
category2_.category_id as category2_0_2_,
category2_.name as name3_0_2_,
category2_.site as site4_0_2_
from item item0_
left outer join category category1_
on item0_.site=category1_.site
and item0_.secondary_category_id=category1_.category_id
left outer join category category2_
on item0_.site=category2_.site
and item0_.primary_category_id=category2_.category_id
如您所见，两个类别表都连接在同一个 SELECT
我有以下实体，一个 item 最多可以有两个类别，一个主要的和一个次要的。
这两个类别都使用 JoinColumnsOrFormulas 映射 ManyToOne 到 category table。
第一个按预期获取 EAGER，但第二个未出现在 SQL 语句中并延迟加载。
这种延迟加载会导致经典的 n+1 问题。
这是我的项目实体，其中包含应该加入的两个类别实体：
@Entity
@Table(name = "item", schema = "public", catalog = "Whosebug_question")
@DynamicUpdate
public class Item extends WhosebugQuestionEntity {
@Id
@Column(name = "id")
protected Long id;
@Column(name = "site")
private String site;
@ManyToOne
@JoinColumnsOrFormulas({
@JoinColumnOrFormula(formula = @JoinFormula(value = "site", referencedColumnName = "site")),
@JoinColumnOrFormula(formula = @JoinFormula(value = "primary_category_id", referencedColumnName = "category_id"))
})
private Category primaryCategory;
@Column(name = "primary_category_id")
private Long primaryCategoryId;
@ManyToOne
@JoinColumnsOrFormulas({
@JoinColumnOrFormula(formula = @JoinFormula(value = "site", referencedColumnName = "site")),
@JoinColumnOrFormula(formula = @JoinFormula(value = "secondary_category_id", referencedColumnName = "category_id"))
})
private Category secondaryCategory;
@Column(name = "secondary_category_id")
private Long secondaryCategoryId;
}
这是类别实体：
@Entity
@Table(name = "category", schema = "public", catalog = "Whosebug_question")
public class Category extends WhosebugQuestionEntity {
@Column(name = "category_id")
private Long categoryId;
@Column(name = "name")
private String name;
@Column(name = "site")
private String site;
}
生成的查询仅包含主要类别：
SELECT this_.id AS id1_9_9_,
this_.inserted AS inserted2_9_9_,
this_.updated AS updated3_9_9_,
this_.primary_category_id AS formula174_9_,
this_.secondary_category_id AS formula176_9_,
category2_.id AS id1_0_0_,
category2_.inserted AS inserted2_0_0_,
category2_.updated AS updated3_0_0_,
category2_.name AS name7_0_0_
FROM public.item this_
LEFT OUTER JOIN public.category category2_ ON this_.site=category2_.site
AND this_.primary_category_id=category2_.category_id
WHERE True;
因此次要类别懒惰加入：
SELECT category0_.id AS id1_0_0_,
category0_.inserted AS inserted2_0_0_,
category0_.updated AS updated3_0_0_,
category0_.name AS name4_0_0_,
category0_.site AS site5_0_0_
FROM public.category category0_
WHERE category0_.site=?
AND category0_.category_id=?;
为什么Hibernate加入secondary category lazy，注解好像是一样的
我使用的hibernate版本是5.0.10.Final.
这是基础实体的样子：
@MappedSuperclass
abstract public class WhosebugQuestionEntity implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Column(name = "id", unique = true, insertable = true, updatable = false, nullable = false)
protected Long id;
@Type(type="LocalDateTime")
@Column(name = "created", nullable = false, insertable = true, updatable = false)
protected LocalDateTime created;
@Type(type="LocalDateTime")
@Column(name = "refreshed", nullable = false, insertable = true, updatable = true)
protected LocalDateTime refreshed;
@PreUpdate
protected void onUpdate() {
refreshed = now();
}
@PrePersist
protected void onCreate() {
created = refreshed = now();
}
}
这里有一个例子"query"，正如我所说的，我正在使用hibernate criteria和HQL，这两种方法都会出现问题。
session
.createCriteria(Item.class)
.add(eq("id", id))
.uniqueResult();
使用标准 JPA 注释，它看起来像这样（已更新）：
@ManyToOne
@JoinColumns({
@JoinColumn(name="site", referencedColumnName="site", insertable = false, updatable = false),
@JoinColumn(name="primary_category_id", referencedColumnName="category_id", insertable = false, updatable = false)
})
private Category primaryCategory;
@ManyToOne
@JoinColumns({
@JoinColumn(name="site", referencedColumnName="site", insertable = false, updatable = false),
@JoinColumn(name="secondary_category_id", referencedColumnName="category_id", insertable = false, updatable = false)
})
private Category secondaryCategory;
更新： 我发现第二个 select 语句仅在您通过复合键使用 join 时生成：Hibernate 尝试解析关联{site=site, id=null} 使用 TwoPhaseLoad。但是如果你写
@ManyToOne
@JoinColumn(name="secondary_category_id")
private Category secondaryCategory;
且secondary_category_id为null则生成唯一的select语句，secondaryCategory值为null。也许它会以某种方式帮助你。例如，您可以在构建条件时对 site 字段添加约束：
Category c = (Category) session.createCriteria(Category.class)
.add(Restrictions.eq("id", 1L)) // for example
// here you define additional restriction on site field
.createAlias("secondaryCategory", "sc", JoinType.LEFT_OUTER_JOIN, Restrictions.sqlRestriction("this_.site = {alias}.site"))
.uniqueResult();
尝试以下解决方案：
@Entity
@Table(name = "item", schema = "public", catalog = "Whosebug_question")
@DynamicUpdate
public class Item {
@ManyToOne
@JoinColumn(name="site")
private Category primaryCategory;
@ManyToOne
@JoinColumn(name="site")
private Category secondaryCategory;
}
@Entity
@Table(name = "category", schema = "public", catalog = "Whosebug_question")
public class Category {
@OneToMany(targetEntity=Item.class, mappedBy="primaryCategory", cascade=CascadeType.ALL)
private List<Item> primaryCategoryList;
@OneToMany(targetEntity=Item.class, mappedBy="secondaryCategory", cascade=CascadeType.ALL)
private List<Item> secondaryCategoryList;
}
我使用您的 类 和以下查询代码（使用 JPA 条件查询而不是本机 Hibernate）进行了快速测试
CriteriaQuery<Item> cq = em.getCriteriaBuilder().createQuery(Item.class);
EntityGraph<Item> entityGraph = em.createEntityGraph(Item.class);
entityGraph.addSubgraph("primaryCategory", Category.class);
entityGraph.addSubgraph("secondaryCategory", Category.class);
List<Item> items = em.createQuery(cq.select(cq.from(Item.class)))
.setHint("javax.persistence.loadgraph", entityGraph)
.getResultList();
导致生成以下 SQL（为了便于阅读而格式化）：
select item0_.id as id1_1_0_,
category1_.id as id1_0_1_,
category2_.id as id1_0_2_,
item0_.site as site4_1_0_,
item0_.primary_category_id as primary_2_1_0_,
item0_.secondary_category_id as secondar3_1_0_,
category1_.category_id as category2_0_1_,
category1_.name as name3_0_1_,
category1_.site as site4_0_1_,
category2_.category_id as category2_0_2_,
category2_.name as name3_0_2_,
category2_.site as site4_0_2_
from item item0_
left outer join category category1_
on item0_.site=category1_.site
and item0_.secondary_category_id=category1_.category_id
left outer join category category2_
on item0_.site=category2_.site
and item0_.primary_category_id=category2_.category_id
如您所见，两个类别表都连接在同一个 SELECT