JPA + Hibernate将一个实体中的java.util.Set映射到另一个实体java.util.Map

Question

我在项目中遇到了JPA + Hibernate映射的问题(我完全是hibernate和jpa的新手，所以请耐心等待:)。

以下是我的实体：

@Entity
@Table(name = "yeasts")
public class Yeast {

...
private Set<BeerRecipe> recipes;
...

@ManyToMany(cascade = CascadeType.ALL)
@JoinTable(name = "recipe_yeasts"
        ,joinColumns = @JoinColumn(name = "yst_id", referencedColumnName = "yst_id")
        ,inverseJoinColumns = @JoinColumn(name = "brp_id", referencedColumnName = "brp_id"))
public Set<BeerRecipe> getRecipes() {
    return recipes;
}

public void setRecipes(Set<BeerRecipe> recipes) {
    this.recipes = recipes;
}
}

第二个是：

@Entity
@Table(name = "beer_recipes")
public class BeerRecipe {

...
private Map<Yeast,Double> yeasts;
...
@ManyToMany(cascade = CascadeType.ALL)
@ElementCollection
@JoinTable(name = "recipe_yeasts"
        ,inverseJoinColumns = @JoinColumn(name = "yst_id", referencedColumnName = "yst_id")
        ,joinColumns = @JoinColumn(name = "brp_id", referencedColumnName = "brp_id"))
public Map<Yeast, Double> getYeasts() {
    return yeasts;
}

public void setYeasts(Map<Yeast, Double> yeasts) {
    this.yeasts = yeasts;
}

...
}

我被困在这里，因为我找不到解决我的问题的办法。我需要我的BeerRecipe对象来存储Map<酵母，Double> (double代表啤酒配方中使用的酵母量)，以及酵母对象来存储Set< BeerRecipe>(多对多关系-使用相同酵母的X啤酒配方和在同一配方中使用的X酵母)

现在我得到了一个异常：

Use of @OneToMany or @ManyToMany targeting an unmapped class: 
my.project.db_model.BeerRecipe.yeasts[java.lang.Double]

Answer 1

示例解决方案：

@Entity
@Table(name = "yeasts")
public class Yeast {

    @Id
    private int yst_id;

    @OneToMany(cascade=CascadeType.ALL, mappedBy="yeasts")
    private Set<BeerRecipe> recipes;

    ...
}

​

​

@Entity
@Table(name = "beer_recipes")
public class BeerRecipe {

    @Id
    private int brd_id;

    @ElementCollection
    @CollectionTable(name = "recipe_yeasts", joinColumns = @JoinColumn(name = "brd_id"))
    @MapKeyJoinColumn(name = "yst_id", referencedColumnName = "yst_id") //refers to Yeast
    @Column(name = "amount") //refers to Double
    private Map<Yeast, Double> yeasts;

    ...
}

通过这种方法，您可以保留beer_recipes和酵母之间的双向关系。该映射代表中间的recipe_yeasts连接表。