Question

假设我们使用以下SQL创建2个表：

create table Supplier (id int, name VARCHAR, count int);
create table Product (id int, name VARCHAR, description VARCHAR, price double, supplierId int);

型号：

公共类供应商{

private int id;

private String name;
private int count;

public int getId(){   return id;}
public void setId(int id){     this.id = id; }

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

public int getCount() {    return count;}
public void setCount(int count) {   this.count = count;}

}

AND

public class Product {

private int id;
private String name;
private String description;
private Double price;
private Supplier supplier;

public int getId() {    return id;}
public void setId(int id) {   this.id = id; }

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

public String getDescription() {    return description;}
public void setDescription(String description) {    this.description = description; }

public Double getPrice() {return price;}
public void setPrice(Double price) {   this.price = price;}

@OneToOne(targetEntity=ProductAssignment.class, mappedBy = "supplierId", fetch = FetchType.LAZY)
public Supplier getSupplier() {    return supplier;}
public void setSupplier(Supplier supplier) {    this.supplier = supplier; }

}

如果我想在供应商中按计数选择所有产品，我可以使用以下代码：

Criteria crit = session.createCriteria(Product.class);
Criteria critSupplier = crit.createCriteria("supplier");
critSupplier.addOrder(Order.desc("count"));

但是现在，我想在Product表中按价格选择所有供应商。

如果我想使用MySQL，下面是脚本： select * from supplier s inner join product p ON s.id = p.supplierId order by p.price

现在我想将这个SQL转移到java代码中的Hibernate Criteria查询中吗？

在这种情况下请帮助我吗？

Answer 1

在这里，您可以在两个模型之间建立双向关系：供应商和产品。它是一种双向关系，因为您希望两个模型彼此了解，并根据连接它们的链接（supplierId）重新收集彼此的信息。这种关系也是一个（供应商） - 多种（产品）

所以，首先，您错过了供应商必须意识到关系存在的事实。您必须通过修改供应商模型来表达这种“意识”，并将其添加到列表产品中：

public class Supplier implements Serializable{
    private int id;
    private String name;
    private int count;
    private List<Product> products;

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public int getCount() {
        return count;
    }

    public void setCount(int count) {
        this.count = count;
    }

    public List<Product> getProducts() {
        return products;
    }

    public void setProducts(List<Product> products) {
        this.products = products;
    }

    @Override
    public String toString() {
        return "Supplier{" + "name=" + name + '}';
    }

第二步是传达ORM（在你的情况下是休眠）两个模型之间的关系。在线你可以找到大量的文档来解释这个微妙的休眠“步骤”。在你的情况下，这样的事情应该做。

供应商的Hibernate映射：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
  "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.xxx.stackoverflowdb.model.Supplier" table="Supplier">
        <id column="id" name="id" type="int">
            <generator class="assigned"/>
        </id>
        <property column="name" name="name" type="string"/>
        <property column="count" name="count" type="int"/>
        <bag name="products" table="product" inverse="true" lazy="false" fetch="select">
            <key>
                <column name="id"/>
            </key>
            <one-to-many class="com.xxx.stackoverflowdb.model.Product"/>
        </bag>
    </class>
</hibernate-mapping>

产品的Hibernate映射：

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-mapping PUBLIC
  "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
  "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="com.xxx.stackoverflowdb.model.Product" table="PRODUCT">
        <id column="id" name="id" type="int">
            <generator class="assigned"/>
        </id>
        <property column="name" name="name" type="string"/>
        <property column="description" name="description" type="string"/>
        <property column="price" name="price" type="double"/>
        <many-to-one name="supplierId" class="com.xxx.stackoverflowdb.model.Supplier" column="supplierId" insert="false" update="false" lazy="false"/>
    </class>
</hibernate-mapping>

如您所见，两个映射文件都声明了这种关系。使用此设置，您可以编写标准并让它完成工作。既然现在hibernate知道这种关系，它可以帮助你。我已经创建了一个简单的测试器类来演示它：

public class Tester {
public static void main(String[] args) {

    //gets a session, assuming your cg file is in a folder called hibernate_dispatcher 
    //under classpath
    SessionFactory sessionFactory = new Configuration().configure("/hibernate_dispatcher/hibernate.cfg.xml")
                                 .buildSessionFactory();
    Session session = sessionFactory.openSession();
    //gets a session, assuming your cg file is in a folder called hibernate_dispatcher 
    //under classpath


    //YOUR own query --> gets all products order by count in supplier
    Criteria criteria1 = session.createCriteria(Product.class);
    criteria1.createAlias("supplierId", "supp");
    criteria1.addOrder(Order.desc("supp.count"));

    for(Object p:criteria1.list()){
        Product nthP=(Product)p;
        System.out.println(nthP);
    }
    //YOUR own query --> gets all products order by count in supplier



    //the query you've asked --> gets all products order by price in Product
    Criteria criteria2 = session.createCriteria(Supplier.class);
    criteria2.createAlias("products", "prod");
    criteria2.addOrder(Order.desc("prod.price"));

    for(Object s:criteria2.list()){
        Supplier nthS=(Supplier)s;
        System.out.println(nthS);
    }
    //the query you've asked --> gets all products order by price in Product
}

}

按其他条件选择和排序列表（Criteria inner join hibernate）

1 个答案: