mysql - 如何修复 "Coult not find Id property. Be sure the accessor method name matches the veriable name"错误

Question

当我按下“完成”按钮时，我创建了“从实体类新建 JPA Controller 类”，然后收到以下错误。

Users.java

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package com.mycompany.mavenproject1.exceptions.exceptions.exceptions;

import java.io.Serializable;
import javax.persistence.Basic;
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.NamedQueries;
import javax.persistence.NamedQuery;
import javax.persistence.Table;
import javax.validation.constraints.NotNull;
import javax.validation.constraints.Size;
import javax.xml.bind.annotation.XmlRootElement;

/**
*
* @author OZGUR-PC
*/
@Entity
@Table(name = "users")
@XmlRootElement
@NamedQueries({
@NamedQuery(name = "Users.findAll", query = "SELECT u FROM Users u"),
@NamedQuery(name = "Users.findById", query = "SELECT u FROM Users u WHERE u.id = :id"),
@NamedQuery(name = "Users.findByUserName", query = "SELECT u FROM Users u WHERE u.userName =       :userName")})
public class Users implements Serializable {
private static final long serialVersionUID = 1L;
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Basic(optional = false)
@Column(name = "id")
private Integer id;
@Basic(optional = false)
@NotNull
@Size(min = 1, max = 50)
@Column(name = "user_name")
private String userName;

public Users() {
}

public Users(Integer id) {
    this.id = id;
}

public Users(Integer id, String userName) {
    this.id = id;
    this.userName = userName;
}

public Integer getId() {
    return id;
}

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

public String getUserName() {
    return userName;
}

public void setUserName(String userName) {
    this.userName = userName;
}

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

@Override
public boolean equals(Object object) {
    // TODO: Warning - this method won't work in the case the id fields are not set
    if (!(object instanceof Users)) {
        return false;
    }
    Users other = (Users) object;
    if ((this.id == null && other.id != null) || (this.id != null && !this.id.equals(other.id)))   {
        return false;
    }
    return true;
}

@Override
public String toString() {
    return "com.mycompany.mavenproject1.exceptions.exceptions.exceptions.Users[ id=" + id + " ]";
}

}

我需要关于如何解决这个问题的想法。预先感谢您的帮助。

Answer 1

确保您已为您的实体声明了标识符。例如，假设有一个名为 Student 的实体，其标识符为 studentId 和属性 name 那么该实体应该是这样的，它应该有 setter以及字段的 getter 方法:

@Entity
public class Student {
    @Id
    @GeneratedValue
    private int studentId;
    private String name;

    public String getName() {
        return name;
    }

    public int getStudentId() {
        return studentId;
    }

    public void setStudentId(int studentId) {
        this.studentId = studentId;
    }

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