spring-boot(二) 整合jpa

相关引入：

1.pom.xml

<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
</dependency>

2. 实体类

UserLogin.java

package cn.springbooot.SpringBootFrist.model;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;
import javax.validation.constraints.NotNull;

@Entity
@Table(name="user")
public class UserLogin {

@Id
@NotNull
@GeneratedValue(strategy=GenerationType.AUTO)
public long id;

@NotNull
@Column(name="password")
public String password;

@NotNull
@Column(name="username")
public String username;

public UserLogin(){};

public UserLogin(String a, String b){
this.username = a;
this.password = b;
}

public long getId() {
return id;
}

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

public String getPassword() {
return password;
}

public void setPassword(String password) {
this.password = password;
}

public String getUsername() {
return username;
}

public void setUsername(String username) {
this.username = username;
}

}

UserLoginDao.java

package cn.springbooot.SpringBootFrist.Dao;

import org.springframework.data.jpa.repository.JpaRepository;
import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.query.Param;

import cn.springbooot.SpringBootFrist.model.UserLogin;

/**
* 1、 几种不同的查询方式
*  1. fingById是通过JpaRepository 来进行查询
*  2. 也可以通过自己书写 sql来进行查询
*  3. 可以写在实体类上
*/
public interface UserLoginDao extends JpaRepository<UserLogin,Long>{

public UserLogin findById(Long id);

@Query("select t from UserLogin t where t.username = ?")
public UserLogin findByUsername1(String username);
// 1 是查询方法中参数的顺序
@Query("select t from UserLogin t where t.username = ?1")
public UserLogin findByUsername2(String username);

@Query("select t from UserLogin t where t.username like %:username%")
public UserLogin findByUsername3(@Param("username")String username);

}

出现错误的地方：

nested exception is

javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory

引起的原因：是由于实体类名称和数据库中不匹配

如果碰到出入bean失败的地方，要从两个方面着手排查，

1. bean 应该有的注解是否正确添加

2. 包扫描的路径是否正确