如何使用 JPA 与关联类建立递归的多对多关系？答案

【问题标题】：How do I set up a recursive, many-to-many relationship WITH an association class using JPA?如何使用 JPA 与关联类建立递归的多对多关系？
【发布时间】：2020-11-15 14:19:08
【问题描述】：

因此，我正在尝试创建一个药房数据库，其中包括跟踪药物与药物之间的相互作用。我有一个拥有各种成员和协会的药物实体，到目前为止，它们似乎都运行良好。我不确定我是否正确的一种实现是使用关联类与 Drug 实体建立递归的多对多关系。关联类 (DrugDrugIX) 有 2 个外键 - 来自每种药物的一个 - 以及该相互作用的严重程度的描述和分配。

到目前为止我所做的工作，因为它将编译和运行，让我添加药物和交互。但是，我当然不认为我正在做的事情是最优化的——甚至不是正确的。关于如何优化我正在尝试做的任何建议？

Drug实体（为简洁起见省略了一些成员）：

@Entity
@Table (name = "drugs")
@NamedQueries({
        @NamedQuery (name = Drug.FIND_ALL_BY_NAME,
                     query = "SELECT d FROM Drug d WHERE LOWER (d.chemical_name) LIKE LOWER (CONCAT ('%', :searchString, '%'))" )
})
public class Drug
{
    // QUERY STRING(S)
    public static final String FIND_ALL_BY_NAME = "Drug.findAllByName";

    @Id
    @GeneratedValue (strategy = GenerationType.IDENTITY)
    private long did;

    private String chemical_name;
    private String description;

    // ASSOCIATION(S)
    is this the correct implementation (???)
<----------------------------------------------------------------------------------->
    @OneToMany (mappedBy = "base", cascade = CascadeType.PERSIST)
    private List<DrugDrugIX> interxAsBase;
    
    @OneToMany (mappedBy = "offender", cascade = CascadeType.PERSIST)
    private List<DrugDrugIX> interxAsOffender;
<----------------------------------------------------------------------------------->

    @ManyToOne (cascade = CascadeType.PERSIST)
    private DEA_Class schedule;

    @OneToOne (cascade = CascadeType.PERSIST)
    private Pharmacology PK_profile;

    (...) other associations, getters and setters here (...)

    public void addInterxAsBase (DrugDrugIX interaction)
    {
        if (this.interxAsBase == null)
            interxAsBase = new ArrayList<>();

        interxAsBase.add (interaction);
    }

    public void addInterxAsOffender (DrugDrugIX interaction)
    {
        if (this.interxAsOffender == null)
            interxAsOffender = new ArrayList<>();

        interxAsOffender.add (interaction);
    }
}

DrugDrugIX 关联实体：

@Entity
@Table (name = "drug_drug_interactions")
public class DrugDrugIX
{
    @EmbeddedId
    private DrugDrugIX_PK interaction_CPK;
    private int severityLevel = -1;
    
    // ASSOCIATION(S)
    @ManyToOne
    @MapsId ("base")
    private Drug base;
    
    @ManyToOne
    @MapsId ("offender")
    private Drug offender;

    (...) getters, setters omitted for brevity (...)

    public void registerInteraction (Drug object, Drug precipitate)
    {
        if (this.base == null)
            this.base = object;
        if (this.offender == null)
            this.offender = precipitate;

        if ((this.base == object && this.offender == precipitate) && (severityLevel == -1))
        {
            object.addInterxAsBase(this);
            precipitate.addInterxAsOffender(this);
        }
    }
}

...为了后代，Embeddable 包含 DrugDrugIX 实体的主键：

@Embeddable
public class DrugDrugIX_PK implements Serializable
{
    private long base;
    private long offender;
    private String description;

    // CONSTRUCTORS
    public DrugDrugIX_PK () {}
    public DrugDrugIX_PK (Drug base, Drug offender, String description)
    {
        this.base = base.getDID();
        this.offender = offender.getDID();
        this.description = description;
    }
    
    // ACCESSORS
    public String getDescription () { return this.description; }

    // MISCELLANEOUS
    @Override
    public boolean equals (Object other)
    {
        if (other instanceof DrugDrugIX_PK)
        {
            DrugDrugIX_PK second = (DrugDrugIX_PK) other;

            return (this.base == second.base) && (offender == second.offender) && (this.description.equals (description));
        }
        else
            return false;
    }

    @Override
    public int hashCode () { return (int) (base + offender); }
}

我向stackoverflow大神祈求指导..

【问题讨论】：

标签： java jpa many-to-many model-associations

【解决方案1】：

您不需要使用递归。只需使用两个嵌套循环。类似这样的伪代码：

drugs = {1, 4, 6}
for drug1 in drugs
    for drug2 in drugs
         get_interaction drug1, drug2

被管理的药物由药物数组中的整数表示。

【讨论】：