如何在hibernate中执行连接查询？

Question

如何在Hibernate中运行join HQL查询？我已将值插入到一对一的关系表中。但在我插入表之前，我需要检查值是否存在。如果退出我需要该记录的id。之后我已插入orderdetails表。

所以，我需要运行SQL来从表中获取ID。

表：产品

Product_id
product_name

表：版本

version_id
product_id
date

所以如果记录存在，我需要找到version_id。我想运行SQL：select version_id from product p,version v where p.product_id=v.product_id and product_name='stackoverflow'

我试过这种方式..

Query q=session.createQuery("from Product p,Version v where p.product_id=v.product_id and productname='"+item+"'");
if(query.list().size()>0){
for(Iterator it=query.iterate();it.hasNext();)
{
Version std = ( Version) it.next();
System.out.println("partid: " + std.getversion_id());
V.setversion_id(std.getversion_id());
 }

但是上面的代码给出了错误。

org.hibernate.QueryException: could not resolve property: product_id of: Version [from Product p,Version v where p.product_id=v.product_id and productname='stack']
    at org.hibernate.persister.entity.AbstractPropertyMapping.propertyException(AbstractPropertyMapping.java:81)
    at org.hibernate.persister.entity.AbstractPropertyMapping.toType(AbstractPropertyMapping.java:75)
    at org.hibernate.persister.entity.AbstractEntityPersister.toType(AbstractEntityPersister.java:1465)
    at org.hibernate.hql.ast.tree.FromElementType.getPropertyType(FromElementType.java:315)
    at org.hibernate.hql.ast.tree.FromElement.getPropertyType(FromElement.java:487)
    at org.hibernate.hql.ast.tree.DotNode.getDataType(DotNode.java:611)
    at org.hibernate.hql.ast.tree.DotNode.prepareLhs(DotNode.java:263)
    at org.hibernate.hql.ast.tree.DotNode.resolve(DotNode.java:210)
    at org.hibernate.hql.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:117)
    at org.hibernate.hql.ast.tree.FromReferenceNode.resolve(FromReferenceNode.java:113)
    at org.hibernate.hql.ast.HqlSqlWalker.resolve(HqlSqlWalker.java:880)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.expr(HqlSqlBaseWalker.java:1330)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.exprOrSubquery(HqlSqlBaseWalker.java:4471)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.comparisonExpr(HqlSqlBaseWalker.java:3947)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.logicalExpr(HqlSqlBaseWalker.java:2047)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.logicalExpr(HqlSqlBaseWalker.java:1972)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.whereClause(HqlSqlBaseWalker.java:831)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.query(HqlSqlBaseWalker.java:617)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.selectStatement(HqlSqlBaseWalker.java:301)
    at org.hibernate.hql.antlr.HqlSqlBaseWalker.statement(HqlSqlBaseWalker.java:244)
    at org.hibernate.hql.ast.QueryTranslatorImpl.analyze(QueryTranslatorImpl.java:256)
    at org.hibernate.hql.ast.QueryTranslatorImpl.doCompile(QueryTranslatorImpl.java:187)
    at org.hibernate.hql.ast.QueryTranslatorImpl.compile(QueryTranslatorImpl.java:138)
    at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:101)
    at org.hibernate.engine.query.HQLQueryPlan.<init>(HQLQueryPlan.java:80)
    at org.hibernate.engine.query.QueryPlanCache.getHQLQueryPlan(QueryPlanCache.java:124)
    at org.hibernate.impl.AbstractSessionImpl.getHQLQueryPlan(AbstractSessionImpl.java:156)
    at org.hibernate.impl.AbstractSessionImpl.createQuery(AbstractSessionImpl.java:135)
    at org.hibernate.impl.SessionImpl.createQuery(SessionImpl.java:1770)
    at com.import(CompleteNotice.java:764)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:723)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:861)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:606)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Thread.java:619)

产品类别：

@Entity
@Table(name="DBO.PRODUCT")
public class Product{

    private String product_id;
    private String product_name

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="PRODUT_ID")
    public String getProduct_id() {
        return product_id;
    }

    public void setProduct_id(String product_id) {
        this.product_id = product_id;
    }

    @Column(name="PRODUCT_NAME")
    public String getProduct_name() {
        return product_name;
    }

    public void setProduct_name(String product_name) {
        this.product_name = product_name;
    }


}

版本：

@Entity
@Table(name="DBO.VERSION")
public class Version {

    private int version_id;
    private int product_id;
    private Product product;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name="VERSION_ID")
    public int getVersion_id() {
        return version_id;
    }

    public void setVersion_id(int Version_id) {
        this.version_id = version_id;
    }


    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="product_id")
    public Product getProduct() {
        return product;
    }

    public void setProduct(Product product) {
        this.product = product;
    }

请告知如何在hibernate中执行上述查询？

Answer 1

首先，在这种情况下，您的类名是Part而不是Product。 因此，您必须在查询中使用Part。

其次我不确定是否有一个能够生成的hibernate id生成器 字符串序列，所以你必须分配一个自定义的id生成器。

此外，您发布的代码并未显示Version类及其类别 与产品或部件的关联。

在我看来，尽管存在id问题，但您的查询应该如下所示

select v.version_id 
from FeatureVersion v, Part p
where v.product.product_id = p.product_id
and p.product_name='"+item+"

执行该查询时。 Hibernate创建一个类型为FeaturedVersion的instamce，并根据关联的表列初始化其属性。

尽量避免使用这种语句。请改用PreparedStatements来传递 查询的参数并使用命名参数左右将它们分配给查询。

尝试使用符合Java和JavaBeans约定的属性和类名 意味着避免低调等等。因此，阅读查询更简单，您可以避免错误搜索。

Answer 2

您的映射很糟糕。 product_id

中不需要FeatureVersion

@Entity
@Table(name="DBO.PRODUCT")
public class Part { // why not call Product..

    private String product_id;
    private String product_name;
    private FeatureVersion version;    

    @OneToOne(mappedBy="product")
    public FeatureVersion getFeatureVersion(){
        return featureVersion;
    }    
      //put others getters and setter 
 }

在另一堂课。

@Entity
@Table(name="DBO.VERSION")
public class FeatureVersion {

    private int version_id;
    private Product product;

    //add setter and getter that i leave

   @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name="product_id", referencedColumnName= "product_id")
    public Product getProduct() {
        return product;
    }

}

在客户端代码中，查询字符串如下所示：

String hql = "FROM Part p fetch join p.version Where p.product_name = :myParam" // this is cause you put it lazy if you don't put anything it will be eager 
session.createQuery(hql).setParameter("myParam", productName).uniqueResult() // or list

一些建议：

1）遵循java代码约定，例如将product_name更改为productName或仅name。 2）在数据库中调用与约定相同名称的类。

3）对于字符串，我会使用like子句而不是=如果你不想要完全匹配。