我正在Java 8使用Spring 4.3.1.RELEASE，JPA 2和Hibernate 5.2.1.Final以及MySQL。
hibernate.dialect = org.hibernate.dialect.MySQLDialect
hibernate.show_sql = true
hibernate.format_sql = true
我有以下代码，它执行简单的SELECT语句：
import java.util.List;
import org.springframework.stereotype.Repository;
import com.jobs.spring.domain.Category;
@Repository("categoryDao")
public class CategoryDaoImpl extends JpaDao<String, Category> implements CategoryDao {
@Override
public List<Category> findAll() {
List<Category> categories = (List<Category>) entityManager.createQuery("Select t from " + entityClass.getSimpleName() + " t order by name").getResultList();
return categories;
}
}
如果我调试代码，这个方法只调用一次，但是从下面的输出可以看出，Hibernate多次执行相同的SQL语句。
10:52:13,960 INFO [stdout] (default task-4) Hibernate: 10:52:13,962 INFO [stdout] (default task-4) select 10:52:13,962 INFO [stdout] (default task-4) category0_.id as id1_0_, 10:52:13,962 INFO [stdout] (default task-4) category0_.ICON as ICON2_0_, 10:52:13,963 INFO [stdout] (default task-4) category0_.CATERGORY as CATERGOR3_0_ 10:52:13,963 INFO [stdout] (default task-4) from 10:52:13,964 INFO [stdout] (default task-4) category category0_ 10:52:13,964 INFO [stdout] (default task-4) order by 10:52:13,965 INFO [stdout] (default task-4) category0_.CATERGORY 10:52:14,399 INFO [stdout] (default task-4) Hibernate: 10:52:14,400 INFO [stdout] (default task-4) select 10:52:14,400 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:14,401 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:14,402 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:14,402 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:14,403 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:14,403 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:14,404 INFO [stdout] (default task-4) from 10:52:14,404 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:14,405 INFO [stdout] (default task-4) where 10:52:14,406 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:14,813 INFO [stdout] (default task-4) Hibernate: 10:52:14,814 INFO [stdout] (default task-4) select 10:52:14,815 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:14,815 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:14,816 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:14,816 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:14,817 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:14,817 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:14,818 INFO [stdout] (default task-4) from 10:52:14,819 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:14,819 INFO [stdout] (default task-4) where 10:52:14,820 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:15,219 INFO [stdout] (default task-4) Hibernate: 10:52:15,220 INFO [stdout] (default task-4) select 10:52:15,221 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:15,221 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:15,222 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:15,222 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:15,223 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:15,223 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:15,224 INFO [stdout] (default task-4) from 10:52:15,225 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:15,225 INFO [stdout] (default task-4) where 10:52:15,226 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:15,637 INFO [stdout] (default task-4) Hibernate: 10:52:15,637 INFO [stdout] (default task-4) select 10:52:15,638 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:15,638 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:15,639 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:15,640 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:15,640 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:15,641 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:15,641 INFO [stdout] (default task-4) from 10:52:15,642 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:15,642 INFO [stdout] (default task-4) where 10:52:15,643 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:16,079 INFO [stdout] (default task-4) Hibernate: 10:52:16,080 INFO [stdout] (default task-4) select 10:52:16,080 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:16,081 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:16,081 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:16,082 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:16,082 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:16,083 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:16,084 INFO [stdout] (default task-4) from 10:52:16,084 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:16,085 INFO [stdout] (default task-4) where 10:52:16,085 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:16,819 INFO [stdout] (default task-4) Hibernate: 10:52:16,819 INFO [stdout] (default task-4) select 10:52:16,820 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:16,820 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:16,821 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:16,822 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:16,822 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:16,823 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:16,824 INFO [stdout] (default task-4) from 10:52:16,824 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:16,825 INFO [stdout] (default task-4) where 10:52:16,825 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:17,943 INFO [stdout] (default task-4) Hibernate: 10:52:17,944 INFO [stdout] (default task-4) select 10:52:17,945 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:17,945 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:17,946 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:17,946 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:17,947 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:17,947 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:17,948 INFO [stdout] (default task-4) from 10:52:17,949 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:17,949 INFO [stdout] (default task-4) where 10:52:17,950 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:19,460 INFO [stdout] (default task-4) Hibernate: 10:52:19,461 INFO [stdout] (default task-4) select 10:52:19,462 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:19,462 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:19,463 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:19,463 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:19,464 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:19,464 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:19,465 INFO [stdout] (default task-4) from 10:52:19,465 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:19,466 INFO [stdout] (default task-4) where 10:52:19,467 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:20,521 INFO [stdout] (default task-4) Hibernate: 10:52:20,521 INFO [stdout] (default task-4) select 10:52:20,522 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:20,523 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:20,523 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:20,524 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:20,524 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:20,525 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:20,525 INFO [stdout] (default task-4) from 10:52:20,526 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:20,526 INFO [stdout] (default task-4) where 10:52:20,527 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:20,965 INFO [stdout] (default task-4) Hibernate: 10:52:20,966 INFO [stdout] (default task-4) select 10:52:20,966 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:20,967 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:20,968 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:20,968 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:20,969 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:20,969 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:20,970 INFO [stdout] (default task-4) from 10:52:20,970 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:20,971 INFO [stdout] (default task-4) where 10:52:20,971 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:21,364 INFO [stdout] (default task-4) Hibernate: 10:52:21,365 INFO [stdout] (default task-4) select 10:52:21,365 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:21,366 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:21,366 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:21,367 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:21,367 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:21,368 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:21,368 INFO [stdout] (default task-4) from 10:52:21,369 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:21,370 INFO [stdout] (default task-4) where 10:52:21,370 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:21,774 INFO [stdout] (default task-4) Hibernate: 10:52:21,774 INFO [stdout] (default task-4) select 10:52:21,775 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:21,775 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:21,776 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:21,777 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:21,777 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:21,778 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:21,778 INFO [stdout] (default task-4) from 10:52:21,779 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:21,779 INFO [stdout] (default task-4) where 10:52:21,780 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:22,194 INFO [stdout] (default task-4) Hibernate: 10:52:22,195 INFO [stdout] (default task-4) select 10:52:22,195 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:22,196 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:22,196 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:22,197 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:22,197 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:22,198 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:22,199 INFO [stdout] (default task-4) from 10:52:22,199 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:22,200 INFO [stdout] (default task-4) where 10:52:22,200 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:22,590 INFO [stdout] (default task-4) Hibernate: 10:52:22,590 INFO [stdout] (default task-4) select 10:52:22,591 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:22,591 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:22,592 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:22,592 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:22,593 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:22,594 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:22,594 INFO [stdout] (default task-4) from 10:52:22,595 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:22,595 INFO [stdout] (default task-4) where 10:52:22,596 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=? 10:52:23,009 INFO [stdout] (default task-4) Hibernate: 10:52:23,010 INFO [stdout] (default task-4) select 10:52:23,010 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_0_, 10:52:23,011 INFO [stdout] (default task-4) subcategor0_.id as id1_21_0_, 10:52:23,012 INFO [stdout] (default task-4) subcategor0_.id as id1_21_1_, 10:52:23,012 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID as CATEGORY4_21_1_, 10:52:23,013 INFO [stdout] (default task-4) subcategor0_.ICON as ICON2_21_1_, 10:52:23,013 INFO [stdout] (default task-4) subcategor0_.SUBCATEGORY as SUBCATEG3_21_1_ 10:52:23,014 INFO [stdout] (default task-4) from 10:52:23,015 INFO [stdout] (default task-4) subcategory subcategor0_ 10:52:23,015 INFO [stdout] (default task-4) where 10:52:23,016 INFO [stdout] (default task-4) subcategor0_.CATEGORY_ID=?
如果有人可以告诉我如何让Hibernate按预期执行一次查询，我将不胜感激。
更新
这是我的Model对象：
Category.java
@Entity
@Table(name="category")
@XmlRootElement(name="category")
public class Category extends AbstractDomain<String> {
@Id
private String id;
@Size(min=3, max=55)
@Column(name = "CATERGORY", nullable = false)
private String name;
@JsonIgnore
@OneToMany(cascade = CascadeType.ALL, fetch=FetchType.EAGER, mappedBy = "category")
private Set<SubCategory> subCategories;
@JsonIgnore
@Basic(fetch=FetchType.LAZY)
@Lob
@Column(name = "ICON", nullable = true)
private byte[] icon;
@Transient
private byte[] icon64;
@XmlElement
public byte[] getIcon64() {
return icon64;
}
public void setIcon64(byte[] icon64) {
this.icon64 = icon64;
}
@XmlElement
public byte[] getIcon() {
return icon;
}
public void setIcon(byte[] icon) {
this.icon = icon;
}
@XmlElement
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
@XmlElement
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Set<SubCategory> getSubCategories() {
return subCategories;
}
public void setSubCategories(Set<SubCategory> subCategories) {
this.subCategories = subCategories;
}
}
更新
感谢您提供以下建议。我将代码更新为以下内容：
public List<Category> findAll() {
List<Category> categories = (List<Category>) entityManager.createQuery("Select t from " + entityClass.getSimpleName() + " t JOIN FETCH com.jobs.spring.domain.SubCategory order by t.name").getResultList();
return categories;
}
但仍然出现错误：
11:29:42,188 INFO [stdout] (default task-2) Hibernate:
11:29:42,188 INFO [stdout] (default task-2) select
11:29:42,188 INFO [stdout] (default task-2) category0_.id as id1_0_,
11:29:42,188 INFO [stdout] (default task-2) category0_.ICON as ICON2_0_,
11:29:42,188 INFO [stdout] (default task-2) category0_.CATERGORY as CATERGOR3_0_
11:29:42,188 INFO [stdout] (default task-2) from
11:29:42,188 INFO [stdout] (default task-2) category category0_
11:29:42,189 INFO [stdout] (default task-2) inner join
11:29:42,189 INFO [stdout] (default task-2) subcategory subcategor1_
11:29:42,189 INFO [stdout] (default task-2) on
11:29:42,189 INFO [stdout] (default task-2) order by
11:29:42,189 INFO [stdout] (default task-2) category0_.CATERGORY
11:29:42,536 WARN [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-2) SQL Error: 1064, SQLState: 42000
11:29:42,537 ERROR [org.hibernate.engine.jdbc.spi.SqlExceptionHelper] (default task-2) You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'order by category0_.CATERGORY' at line 1
11:29:43,306 ERROR [io.undertow.request] (default task-2) UT005023: Exception handling request to /jbosswildfly-1.0/category/list: org.springframework.web.util.NestedServletException: Request processing failed; nested exception is javax.persistence.PersistenceException: org.hibernate.exception.SQLGrammarException: could not extract ResultSet
更新
我将代码更新为以下内容：
List<Category> categories = (List<Category>) entityManager.createQuery("Select c from Category c JOIN FETCH c.subCategories s order by c.name").getResultList();
哪个没有错误，但它只返回类别的副本，而不返回SubCategories。所以我很瘦，我需要改变SELECT中的内容。
我试过了：
SELECT * (unexpected token: * near line 1)
SELECT c, s (same as SELECT c)
答案 0 :(得分：4)
这是因为您的Category类引用了其他类别，称为subcategory。对于每个类别，您需要获取所有子类别，因此您可以获得许多子查询。我们称之为SQL N + 1问题。我们尝试使用FETCH JOIN：
SELECT c FROM category c JOIN FETCH c.subCategories
应该执行一个（更大的）查询。