JPA中外键关联实体@OneToMany的使用_jparepository onetomany用法

首先介绍我们的表结构，便于理解我们的demo，从而了解两个标签的使用

表结构

pet表，id主键，name宠物名，owner主人，age年纪，category_id外键关联category表
这里一个category对应多个pet，所以category是我们的一端，pet是我们的多端

category表，id主键，category_name种类名，category_code种类编码

标签的使用

@OneToMany的使用在一端的集合属性上面，用于指定与之关联的多个实体

代码：
CategoryEntity实体类

@Entity
@Table(name = "category")
public class CategoryEntity extends BaseEntity{
    @Column
    private String categoryName;
    @Column
    private String categoryCode;

    @OneToMany(cascade = {CascadeType.ALL}, fetch = FetchType.LAZY)
    @JoinColumn(name = "category_id ")
    private Set<PetEntity> pets;

    public CategoryEntity() {
    }

    public CategoryEntity(String categoryName, String categoryCode, Set<PetEntity> pets) {
        this.categoryName = categoryName;
        this.categoryCode = categoryCode;
        this.pets = pets;
    }

    public String getCategoryName() {
        return categoryName;
    }

    public void setCategoryName(String categoryName) {
        this.categoryName = categoryName;
    }

    public String getCategoryCode() {
        return categoryCode;
    }

    public void setCategoryCode(String categoryCode) {
        this.categoryCode = categoryCode;
    }

    public Set<PetEntity> getPets() {
        return pets;
    }

    public void setPets(Set<PetEntity> pets) {
        this.pets = pets;
    }
}
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@OneToMany中mappedBy属性的作用跟@Join Column标签一样，都是由于指定关联键的，mappedBy指定的是实体类中的属性，@JoinColumn指定的是数据表里面的字段

例：
我们在@JoinColumn中name设置为实体中的属性“categoryId”便会报错：找不到表中对应的categoryId

同样我们在mappedBy中应该使用实体属性，使用表字段也会报错

PetEntity实体类

@Entity
@Table(name = "pet")
public class PetEntity extends BaseEntity{
    @Column
    private String name;
    @Column
    private String owner;
    @Column
    private String age;
    @Column(name = "category_id")
    private String categoryId;

    public PetEntity() {
    }

    public PetEntity(String name, String owner, String age,String categoryId) {
        this.name = name;
        this.owner = owner;
        this.age = age;
        this.categoryId=categoryId;
    }

    public String getName() {
        return name;
    }

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

    public String getOwner() {
        return owner;
    }

    public void setOwner(String owner) {
        this.owner = owner;
    }

    public String getAge() {
        return age;
    }

    public void setAge(String age) {
        this.age = age;
    }

    public String getCategoryId() {
        return categoryId;
    }

    public void setCategoryId(String categoryId) {
        this.categoryId = categoryId;
    }
}

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