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