一個Strategy可以包含多條StrategyItem, 但一個StrategyItem只能對應一個Strategy。

資料庫的結構如：

strategy：

關聯表strategy_strategy_item:

strategy_item:

類定義如：

Strategy：

package com.zk.model;

import io.swagger.annotations.ApiModelProperty;
import org.hibernate.annotations.Proxy;

import javax.persistence.*;
import java.util.Date;
import java.util.List;
import java.util.Set;

@Entity
@Table(name = "strategy")
@Proxy(lazy = false)
public class Strategy {
    private Integer id;
   
    //
    // fields definition
    //

    private Set<StrategyItem> strategyItems;

    @Column(name = "id")
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public Integer getId() {
        return id;
    }

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

    //
    // fields getter and setter
    //

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinTable(name="strategy_strategy_item",
            joinColumns=@JoinColumn(name="strategyId", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="strategyItemId", referencedColumnName="id"))
    public Set<StrategyItem> getStrategyItems() {
        return strategyItems;
    }

    public void setStrategyItems(Set<StrategyItem> strategyItems) {
        this.strategyItems = strategyItems;
    }
}
 

主要理解：

    @OneToMany(cascade = CascadeType.ALL, fetch = FetchType.EAGER)
    @JoinTable(name="strategy_strategy_item",
            joinColumns=@JoinColumn(name="strategyId", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="strategyItemId", referencedColumnName="id"))
    public Set<StrategyItem> getStrategyItems() {
        return strategyItems;
    }
 

StrategyItem:

package com.zk.model;

import javax.persistence.*;

@Entity
@Table(name = "strategy_item")
public class StrategyItem {
    private int id;
    
    //
    // fields definition
    //

    private Strategy strategy;

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    public int getId() {
        return id;
    }

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

    // fields getter and setter

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinTable(name="strategy_strategy_item",
            joinColumns=@JoinColumn(name="strategyItemId", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="strategyId", referencedColumnName="id"))
    public Strategy getStrategy() {
        return strategy;
    }

    public void setStrategy(Strategy strategy) {
        this.strategy = strategy;
    }
}
 

主要理解：

    @ManyToOne(cascade = CascadeType.ALL)
    @JoinTable(name="strategy_strategy_item",
            joinColumns=@JoinColumn(name="strategyItemId", referencedColumnName="id"),
            inverseJoinColumns=@JoinColumn(name="strategyId", referencedColumnName="id"))
    public Strategy getStrategy() {
        return strategy;
    }

注意： @ManyToOne和@OneToMany並非一定要成對使用，它們用於修飾一個欄位，這個例子中的Strategy和StrategyItem的關係平等。

測試用例如：

@RunWith(SpringRunner.class)
@SpringBootTest
public class StrategyServiceImplTest {

    @Autowired
    private StrategyRepository strategyRepository;

    @Autowired
    private StrategyItemRepository strategyItemRepository;

    @Test
    public void testSaveStrategyItem() {
        StrategyItem strategyItem1 = new StrategyItem();
        strategyItem1.setPrice("策略價格1");

        StrategyItem strategyItem2 = new StrategyItem();
        strategyItem2.setPrice("策略價格2");

        Set<StrategyItem> strategyItems = new HashSet<>();
        strategyItems.add(strategyItem1);
        strategyItems.add(strategyItem2);

        Strategy strategy = new Strategy();
        strategy.setStrategyItems(strategyItems);
        Strategy savedStrategy = strategyRepository.save(strategy);

        System.out.println(JSON.toJSONString(savedStrategy));

    }

    @Test
    public void testGetStrategyItem() {
        Optional<StrategyItem> strategyItemOptional = strategyItemRepository.findById(5);
        if(strategyItemOptional.isPresent()) {
            System.out.println(JSON.toJSONString(strategyItemOptional.get()));
        }
    }

    @Test
    public void testUpdateStrategy() {
        Optional<Strategy> strategyOptional = strategyRepository.findById(28);

        if(strategyOptional.isPresent()) {
            Strategy strategy = strategyOptional.get();
            Set<StrategyItem> strategyItems = strategy.getStrategyItems();
            strategyItems.remove(strategyItems.iterator().next());
            strategy.setStrategyItems(strategyItems);
            strategyRepository.save(strategy);
        }
    }
} 

PS：JPA的修飾要麼都放在欄位定義上，要麼都放在get方法上，混合使