MyBatis与MycatDao如何实现外键查询

一丶 MyBatis 查询

首先来看下表结构:

user(用户信息表)表的id是user_role(用户权限中间表)中的user_id的外键

使用MyBatis联结查询我们需要如下配置和代码: 实体对象:

// User

@Getter
@Setter
@TableName("user")
public class User extends BaseEntity {

    private String name;
    
    private String password;

    private  List roles;
}

//用户权限关系中间表

@Getter
@Setter
@TableName("user_role")
public class RoleRe {
    private String userId;

    private String roleId;

}

web层:

    @GetMapping("/testFind")
    public User testFind() {
        return userService.testFind();
    }

servre层:

    public User testFind() {
        return userMapper.leftJionRole();
    }

mapper层:

    User leftJionRole();

xml配置:

    
        
        
        
        
        
        
            
        
    


    
        SELECT id,u.name,u.password, ur.role_id FROM user u, user_role ur WHERE u.id = ur.user_id
    

xml是MyBatis的一大优势,xml允许更自由的操作动态sql,但是在带来便利的同时也增加了相应的配置操作,我们如果要使用关联查询,如果返回的对象其中有一个是集合属性就必须配置collection并且要指定类型ofType查询结果:

{
    "id": 3,
    "name": "test",
    "password": "111111",
    "roles": [
        {
            "userId": null,
            "roleId": "3"
        },
        {
            "userId": null,
            "roleId": "2"
        }
    ]
}

这里的userId为空是显而易见的,因为并没有在result中配置userId的映射字段,所以返回的结果为null,这样的小失误也经常发生在开发中

二丶 MycatDao 查询

实体对象

@Getter
@Setter
//mycatDao 会映射实体的大小写转为下划线
public class UserRole {
    //需要告知mycatDao这个字段为外键
    @ForeginKey(value = User.class)
    private String userId;

    private String roleId;

}

    @GetMapping(value = "/test/user", produces = "application/json")
    public JsonValue getUserInfoList() {
        //分页对象及状态码
        PageResultSet result = new PageResultSet();
        JsonValue jsonRest = null;
        try {

            PagedQuery qry = new PowerDomainQuery()
                    //去除重复字段
                    .withAutoRemoveDupFields(true)
                    //添加第一个属性User,并忽略返回字段id
                    .addDomainFieldsExclude(User.class, new String[] { "id" })
                    //添加第二个属性 用户权限关联表
                    .addDomainFieldsExclude(UserRole.class, null);
            //执行查询
            jsonRest = leaderDao.exePagedQuery(qry);
        } catch (Exception e) {
            result.retCode = -1;
            jsonRest = Json.createValue("error:" + e.toString());
        }
        return jsonRest;
    }

响应结果

[
    {
        "name": {
            "chars": "test",
            "string": "test",
            "valueType": "STRING"
        },
        "password": {
            "chars": "111111",
            "string": "111111",
            "valueType": "STRING"
        },
        "roles": {
            "chars": "user,admin1",
            "string": "user,admin1",
            "valueType": "STRING"
        },
        "userId": {
            "integral": true,
            "valueType": "NUMBER"
        },
        "roleId": {
            "integral": true,
            "valueType": "NUMBER"
        }
    },
    {
        "name": {
            "chars": "test",
            "string": "test",
            "valueType": "STRING"
        },
        "password": {
            "chars": "111111",
            "string": "111111",
            "valueType": "STRING"
        },
        "roles": {
            "chars": "user,admin1",
            "string": "user,admin1",
            "valueType": "STRING"
        },
        "userId": {
            "integral": true,
            "valueType": "NUMBER"
        },
        "roleId": {
            "integral": true,
            "valueType": "NUMBER"
        }
    }
]

在操作上MycatDao简化了很多操作来方便开发者,这一点会在开发效率上得到明显的体现,但是MycatDao在响应结果上体验感逊色于MyBatis,这一点相信在未来的发展中会得到改善