mybatis的注解开发

准备的model:

public class User implements Serializable{
    private Integer id;
    private String name;
    
    //保存一对多查询结果
    private List<Account> accounts;
    public List<Account> getAccounts() {
        return accounts;
    }
    public void setAccounts(List<Account> accounts) {
        this.accounts = accounts;
    }
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", name=" + name + "]";
    }

    
    
    
}

public class TUser implements Serializable{
    @Override
    public String toString() {
        return "TUser [userId=" + userId + ", userName=" + userName + "]";
    }
    public int getUserId() {
        return userId;
    }
    public void setUserId(int userId) {
        this.userId = userId;
    }
    public String getUserName() {
        return userName;
    }
    public void setUserName(String userName) {
        this.userName = userName;
    }
    int userId;
    String userName;
}

public class Account implements Serializable{
    private Integer id;
    private Integer uid;
    private double money;
    
    //从表包含一个主表实体
    private User user;

    public Integer getId() {
        return id;
    }

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

    public Integer getUid() {
        return uid;
    }

    @Override
    public String toString() {
        return "Account [id=" + id + ", uid=" + uid + ", money=" + money + ", user=" + user+ "]";
    }

    public void setUid(Integer uid) {
        this.uid = uid;
    }

    public double getMoney() {
        return money;
    }

    public void setMoney(double money) {
        this.money = money;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }
}

　　提示：TUser.java是user.java的别名版。

使用步骤核心：

　　创建对应dao的interface，并在对应的方法上添加sql语句对应的注解。

　　在方法上添加注解，可以根据方法的返回值参数等自动识别，实现想要的效果。

1，单表操作(写在对应的interface中的)

@Select，@Insert,@Update,@Delete注解对应CRUD操作

//针对crud一共有4个注解
    @Select("select * from user")
    public List<User> findAll();
    @Insert("insert into user(name) values(#{name})")
    void saveUser(User user);//#{}里面的变量是对应的形参的属性名
    
    @Update("update user set name=#{name} where id=#{id} ")
    void updateUser(User user);
    
    @Delete("delete from user where id=#{id}")
    void deleteUser(Integer id);
    
    @Select("select * from user where id=#{id}")
    User findById(Integer id);
    

别名的使用

//数据库和对应的表不能对应上
    @Select("select * from user")
    @Results(id="userMap",value = {
            @Result(id=true,column = "id",property = "userId"),
            @Result(column = "name",property = "userName"),
    })
    List<TUser> findTUser();
    
    

    @Select("select * from user where id=#{id}")
    @ResultMap(value = {"userMap"})
    TUser findByIdTUser(Integer id);

2，多表操作

（1）多对一，一对一

fetchType属性：立即加载|懒加载

//多对一查询
    @Select("select a.id,a.money ,a.user_id uid from my_account a ")
    @Results(id="userAccount",value ={
            @Result(id=true,column = "id",property = "id"),
            @Result(column = "uid",property = "uid"),
            @Result(column = "money",property = "money"),
            @Result(column = "uid",property = "user",one=@One(select = "com.dao.IUserDao.findById",fetchType = FetchType.EAGER)),
    })
    
    List<Account> findAccount();
    
    
    //根据uid在account中查询账户
    @Select("select a.id ,a.money,a.user_id uid from my_account a where user_id=#{id}")
    List<Account> findAccountsByUid(Integer uid);
    

（2）一对多

//一对多查询
    @Select("select * from user")
    @Results(id="UserAccountMap",value = {
            @Result(id=true,column = "id",property = "id"),
            @Result(column = "name",property = "name"),
            @Result(column = "id",property = "accounts",many = @Many(select = "com.dao.IUserDao.findAccountsByUid",
            fetchType = FetchType.LAZY
            ))
            
    }
    )
    List<User> findOneToMany();