为什么hibernate无法保存？

Question

我正在使用 Flyway 尝试在 Spring Boot Web 应用程序启动时创建一个数据库，然后为其播种。 Flyway 在第一次迁移中成功创建了数据库表，但由于 NullPointerException 在第二次中未能填充它们。

这是迁移代码，名为 V2_seed_database.java，位于包 db.migration 中：

package db.migration;

import org.flywaydb.core.api.migration.BaseJavaMigration;
import org.flywaydb.core.api.migration.Context;

import net.tekknow.medaverter.db.seeds.AppointmentSeeder;

public class V2__seed_database extends BaseJavaMigration {
    public void migrate(Context context) {
        AppointmentSeeder appointmentSeeder = new AppointmentSeeder();
        appointmentSeeder.seed();
    }
}

这是 AppointmentSeeder 代码：

package net.tekknow.medaverter.db.seeds;

import org.json.JSONArray; 
import org.json.JSONObject;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import net.tekknow.medaverter.domain.Appointment;
import net.tekknow.medaverter.service.AppointmentService;

@Service
public class AppointmentSeeder {
    @Autowired
    AppointmentService appointmentService;

    @PostConstruct
    public void seed() {
        String json = "[" +
            "{\"id\":1,\"patient_id\":1,\"dateTime\":\"10/29/2010\",\"physician_id\":1,\"lab_id\":1,\"note_id\":0}" +
        "]";
        org.json.JSONArray appointments = new JSONArray(json);

        for (int i=0; i<appointments.length(); i++) {
            JSONObject appointment = appointments.getJSONObject(i);
            Appointment dbAppointment = new Appointment();
            dbAppointment.setId(appointment.getInt("id"));
            dbAppointment.setPatientId(appointment.getInt("patient_id"));
            dbAppointment.setDateTime(appointment.getString("dateTime"));
            dbAppointment.setPhysicianId(appointment.getInt("physician_id"));
            dbAppointment.setLabId(appointment.getInt("lab_id"));
            dbAppointment.setNoteId(appointment.getInt("note_id"));
            appointmentService.save(dbAppointment);
        }
    }
}   

这里是 AppointmentRepository 代码：

package net.tekknow.medaverter.db;

import org.springframework.data.jpa.repository.JpaRepository;
import net.tekknow.medaverter.domain.Appointment;

public interface AppointmentRepository extends JpaRepository<Appointment,Integer> {
}

这里是 AppointmentService 代码：

package net.tekknow.medaverter.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;

import net.tekknow.medaverter.db.AppointmentRepository;
import net.tekknow.medaverter.domain.Appointment;

@Service
@Transactional
public class AppointmentService {

    @Autowired
    AppointmentRepository repo;

    public void save(Appointment appointment) {
        System.out.println("AppointmentService.save: appointment="+appointment.toString());
        repo.save(appointment);  //its failing here
    }  
}

这是约会 bean：

package net.tekknow.medaverter.domain;

import javax.persistence.*;
import javax.validation.constraints.NotBlank;
import javax.validation.constraints.Size;

@Entity
@Table(name = "appointments")
public class Appointment {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private int id;
    @NotBlank
    @Column(unique = true)
    private int patient_id;
    @Size(max = 32)
    private String date_time;
    private int physician_id;
    private int lab_id;
    private int note_id;

    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
... other getters and setters, truncated for brevity

当我运行程序时，迁移开始但在这一行失败：

    repo.save(appointment);  //its failing here

带有以下错误消息：

原因：java.lang.NullPointerException: null at net.tekknow.medaverter.service.AppointmentService.save（AppointmentService.java:32） ~[classes/:na]

就在失败的代码行之前，我输出了它说是空的对象的内容，它不是空的：

AppointmentService.save: 约会=id:1, patient_id:1, 日期时间：2010 年 10 月 29 日，医师 ID：1，实验室 ID：1，注释 ID：0

有什么建议吗？

Answer 1

这与休眠无关，您正在以不正确的方式使用 spring 依赖注入：您正在尝试自动装配静态字段，这是不允许的。

见Can you use @Autowired with static fields?。

更新

现在你有

AppointmentService appointmentService = new AppointmentService();

而不是将此字段注入播种机。

如果你想让依赖注入工作，Seeder 需要是一个 Spring 管理的 bean（可能是@Service）。另请参阅@PostConstruct，您可以在 bean 初始化后使用它来调用方法。

更新 2

您仍在使用 new 自己实例化 Spring bean，因此不会注入您的依赖项。

AppointmentSeeder appointmentSeeder = new AppointmentSeeder();

但是，您已成功地将问题推向 Flyway。现在的问题是 Flyway 迁移不是 Spring bean：它们是由 Flyway 创建的，而不是 Spring，因此它们的依赖关系没有由 Spring 自动装配。

Flyway 4.1 通过允许使用预先存在的 Spring bean（或其他 Java 对象）和一些配置解决了这个问题

见API: Make it possible to use pre-instantiated Java-based migrations #1062。

ApplicationContext applicationContext = ...; // obtain a reference to Spring's ApplicationContext.

Flyway flyway = Flyway.configure()
    .dataSource(url, user, password)
    // Add all Spring-instantiated JavaMigration beans
    .javaMigrations(applicationContext.getBeansOfType(JavaMigration.class).values().toArray(new JavaMigration[0]))
    .load();
flyway.migrate();

另请参阅 JavaMigration 和 BaseJavaMigration javadoc。

Answer 2

也许您应该将 JSON 文件中的 ** note_id** 的值更改为 1 ！

Answer 3

在 AppointmentSeeder 中执行此操作，

@Autowire
AppointmentService service;

public void seed() {
        String json = "[" +
            "{\"id\":1,\"patient_id\":1,\"dateTime\":\"10/29/2010\",\"physician_id\":1,\"lab_id\":1,\"note_id\":0}" +
        "]";
        org.json.JSONArray appointments = new JSONArray(json);

        for (int i=0; i<appointments.length(); i++) {
            JSONObject appointment = appointments.getJSONObject(i);
            Appointment dbAppointment = new Appointment();
            dbAppointment.setId(appointment.getInt("id"));
            dbAppointment.setPatientId(appointment.getInt("patient_id"));
            dbAppointment.setDateTime(appointment.getString("dateTime"));
            dbAppointment.setPhysicianId(appointment.getInt("physician_id"));
            dbAppointment.setLabId(appointment.getInt("lab_id"));
            dbAppointment.setNoteId(appointment.getInt("note_id"));
            service.save(dbAppointment);
        }
    }