JPA OneToMany 双向关系 [EclipseLink-63] 错误

Question

请问您能帮帮我吗？在 JPA 中，我尝试创建 OneToMany 双向关系，但出现以下错误： "[EclipseLink-63] : 实例创建方法[entity.OrderLine.]，无参数，不存在，或不可访问。 [EclipseLink-28019]：PersistenceUnit [simple-jpaPU] 的部署失败。关闭此 PersistenceUnit 的所有工厂。”

有我的实体： 一对多实体：

package entity;
import java.util.*;
import java.io.Serializable;
import javax.persistence.*;
import org.eclipse.persistence.annotations.TimeOfDay;

@Entity
public class Order implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Temporal(TemporalType.TIMESTAMP)
    private Date creationDate;    
    @OneToMany(mappedBy = "o")
    private   List<OrderLine>  orderLines; 

    public Date getCreationDate() {
        return creationDate;
    }

    public void setCreationDate(Date creationDate) {
        this.creationDate = creationDate;
    }

    public List<OrderLine> getOrderLines() {
        return orderLines;
    }

    public void setOrderLines(ArrayList<OrderLine> orderLines) {
        this.orderLines = orderLines;
    }

    public Order(Date creationDate) {
        this.creationDate = creationDate;
    }

    public Long getId() {
        return id;
    }

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

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }

    @Override
    public String toString() {
    return "entity.Order[ id=" + id + " ]";
    }
}

多对一实体：

package entity;

import java.io.Serializable;
import javax.persistence.*;

@Entity
@Table(name="orderline_table")
public class OrderLine implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    private String item; 
    private  Double unitPrice;   
    private Integer quantity;
    @ManyToOne
    Order o; 

    public String getItem() {
        return item;
    }

    public void setItem(String item) {
        this.item = item;
    }

    public Double getUnitPrice() {
        return unitPrice;
    }

    public void setUnitPrice(Double unitPrice) {
        this.unitPrice = unitPrice;
    }

    public Integer getQuantity() {
        return quantity;
    }

    public void setQuantity(Integer quantity) {
        this.quantity = quantity;
    }

    public OrderLine(String item, Double unitPrice, Integer quantity) {
        this.item = item;
        this.unitPrice = unitPrice;
        this.quantity = quantity;
    }

    public Long getId() {
        return id;
    }

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

    @Override
    public int hashCode() {
        int hash = 0;
        hash += (id != null ? id.hashCode() : 0);
        return hash;
    }


    @Override
    public String toString() {
        return "entity.OrderLine[ id=" + id + " ]";
    }    
}

Answer 1

它失败是因为OrderLine 没有无参数构造函数。如 JPA 2.1 规范（第 2.1 章）所述，它是必需的：

实体类必须有一个无参数的构造函数。实体类也可能有其他构造函数。无参数构造函数必须是公共的或受保护的。

没有生成默认构造函数，因为给出了其他构造函数。可以通过添加以下构造函数来解决问题：

public OrderLine() {
}