MyBatis 中使用 Association 嵌套查询

红太狼 2022-06-04 03:44 324阅读 0赞

> 当使用 MyBatis 进行查询的时候如果一个 JavaBean 中包含另一个 JavaBean 或者 Collection 时，可以通过 MyBatis 的嵌套查询来获取需要的结果;  
> 以下以用户登录时的用户、角色和菜单直接的关系为例使用嵌套查询

--------------------

## JavaBean ##

*  UserModel

public class UserModel {
        private Integer id;
        private String username;
        private String password;
        private Boolean enabled;
        private Boolean locked;
        private Boolean expired;
        private RoleModel role;
        private List<MenuModel> menus;
    
        ···
    }

*  RoleModel

public class RoleModel {
        private Integer id;
        private String name;
        private Boolean isActive;
        private String description;
        private Date lastUpdateTime;
    
        ···
    }

## 表 ##

*  User

CREATE TABLE user ( id INT AUTO_INCREMENT PRIMARY KEY, username VARCHAR(45) NOT NULL, password VARCHAR(45) NOT NULL, enabled BOOLEAN NOT NULL DEFAULT TRUE, expired BOOLEAN NOT NULL DEFAULT TRUE, locked BOOLEAN NOT NULL DEFAULT TRUE, last_update_time TIMESTAMP NOT NULL DEFAULT current_timestamp ON UPDATE current_timestamp, comment VARCHAR(100) );
    
    INSERT INTO user (username, password, enabled, expired, locked, last_update_time) VALUES ('admin', 'admin', TRUE, FALSE, FALSE, current_timestamp);
    INSERT INTO user (username, password, enabled, expired, locked, last_update_time) VALUES ('user', 'password', TRUE, FALSE, FALSE, current_timestamp);

*  Role

CREATE TABLE role ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, name VARCHAR(50) NOT NULL UNIQUE, description VARCHAR(100), is_active BOOLEAN NOT NULL DEFAULT TRUE, last_update_time TIMESTAMP DEFAULT current_timestamp ON UPDATE current_timestamp );
    
    INSERT INTO role (name, description, is_active, last_update_time) VALUES ('ROLE_ADMIN', 'Administrator', TRUE, current_timestamp);
    INSERT INTO role (name, description, is_active, last_update_time) VALUES ('ROLE_USER', 'User', TRUE, current_timestamp);

*  UserRoleXref

CREATE TABLE user_role_xref ( id INT NOT NULL AUTO_INCREMENT PRIMARY KEY, user_id INT NOT NULL, role_id INT NOT NULL, last_update_time TIMESTAMP NOT NULL DEFAULT current_timestamp ON UPDATE current_timestamp, CONSTRAINT FOREIGN KEY fK_user_role_xref_user_id_user_id (user_id) REFERENCES user (id), CONSTRAINT FOREIGN KEY fk_user_role_xref_role_id_role_id (role_id) REFERENCES role (id) );
    
    INSERT INTO user_role_xref (user_id, role_id, last_update_time) VALUES (1, 1, CURRENT_TIMESTAMP);
    INSERT INTO user_role_xref (user_id, role_id, last_update_time) VALUES (2, 2, CURRENT_TIMESTAMP);

--------------------

## 一个查询调用另一个查询实现的嵌套 ##

<resultMap id="BaseUserModelResultMap" type="cn.com.hellowood.springsecurity.model.UserModel">
            <id column="id" property="id" javaType="java.lang.Integer" jdbcType="INTEGER"></id>
            <result column="username" property="username" javaType="java.lang.String" jdbcType="VARCHAR"></result>
            <result column="password" property="password" javaType="java.lang.String" jdbcType="VARCHAR"></result>
            <result column="enabled" property="enabled" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <result column="expired" property="expired" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <result column="locked" property="locked" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <association property="role" javaType="cn.com.hellowood.springsecurity.model.RoleModel"
                         column="id" select="getRoleByUserId">
            </association>
        </resultMap>
    
        <resultMap id="BaseRoleResultMap" type="cn.com.hellowood.springsecurity.model.RoleModel">
            <id column="id" property="id" jdbcType="INTEGER"/>
            <result column="name" property="name" jdbcType="VARCHAR"/>
            <result column="is_active" property="isActive" jdbcType="BOOLEAN"/>
            <result column="description" property="description" jdbcType="VARCHAR"/>
            <result column="last_update_time" property="lastUpdateTime" jdbcType="TIMESTAMP"/>
        </resultMap>
    
        <select id="getAllUsers" resultMap="BaseUserModelResultMap">
            SELECT
                id,
                username,
                password,
                enabled,
                expired,
                locked
            FROM user
        </select>
    
        <select id="getRoleByUserId" parameterType="java.lang.Integer"
                resultType="cn.com.hellowood.springsecurity.model.RoleModel">
            SELECT
                r.id,
                r.name,
                r.is_active,
                r.description,
                r.last_update_time
            FROM role r
                LEFT JOIN user_role_xref urx
                    ON r.id = urx.role_id
            WHERE user_id = #{userId, jdbcType=INTEGER}
        </select>

> 此时，调用 `getAllUsers()` 方法就可以通过嵌套查询同时查找 Role 属性了

>  *  association : 一个复杂的类型关联，许多结果将映射为这种类型
>  *  property : 这是关联的 JavaBean 中的属性名， 在 UserModel 中对应 `private RoleModel role;`
>  *  column : UserModel 的 id ，作为参数传入被调用的 Select 语句
>  *  select : 另外一个映射语句的 ID

--------------------

## 同一个查询映射到属性的嵌套 ##

> 如果再一个查询中可以直接查询到所需要的数据，但是需要映射到该对象的属性上，则可以使用该方式

<resultMap id="BaseUserModelResultMap" type="cn.com.hellowood.springsecurity.model.UserModel">
            <id column="id" property="id" javaType="java.lang.Integer" jdbcType="INTEGER"></id>
            <result column="username" property="username" javaType="java.lang.String" jdbcType="VARCHAR"></result>
            <result column="password" property="password" javaType="java.lang.String" jdbcType="VARCHAR"></result>
            <result column="enabled" property="enabled" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <result column="expired" property="expired" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <result column="locked" property="locked" javaType="java.lang.Boolean" jdbcType="BOOLEAN"></result>
            <association property="role" javaType="cn.com.hellowood.springsecurity.model.RoleModel">
                <id column="id" property="id" jdbcType="INTEGER"/>
                <result column="name" property="name" jdbcType="VARCHAR"/>
                <result column="is_active" property="isActive" jdbcType="BOOLEAN"/>
                <result column="description" property="description" jdbcType="VARCHAR"/>
                <result column="last_update_time" property="lastUpdateTime" jdbcType="TIMESTAMP"/>
            </association>
        </resultMap>
    
        <select id="getAllUsers" resultMap="BaseUserModelResultMap">
            SELECT
                u.id,
                u.username,
                u.password,
                u.enabled,
                u.expired,
                u.locked,
                r.id,
                r.name,
                r.is_active,
                r.description,
                r.last_update_time
            FROM user u
                LEFT JOIN user_role_xref ur
                    ON u.id = ur.user_id
                LEFT JOIN role r
                    ON ur.role_id = r.id
        </select>