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角色和菜单直接的关系为例使用嵌套查询
JavaBean
- RoleModel
public class RoleModel {
private Integer id;
private String name;
private Boolean isActive;
private String description;
private Date lastUpdateTime;
private List<MenuModel> menus;
···
}
- MenuModel
public class MenuModel {
private Integer id;
private String value;
private String displayValue;
private String url;
private Integer category;
private String description;
private Boolean isActive;
private Date lastUpdateTime;
···
}
表
- 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);
- Menu
CREATE TABLE menu (
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
value VARCHAR(100) NOT NULL,
display_value VARCHAR(100) NOT NULL,
url VARCHAR(100) NOT NULL,
category INT,
description VARCHAR(100),
is_active BOOLEAN NOT NULL DEFAULT TRUE,
last_update_time TIMESTAMP DEFAULT current_timestamp ON UPDATE current_timestamp
);
INSERT INTO menu (value, display_value, url, description, is_active, last_update_time)
VALUES ('/admin/dashboard', 'Admin Dashboard', '/admin/dashboard', 'Admin Dashboard', TRUE, current_timestamp);
INSERT INTO menu (value, display_value, url, description, is_active, last_update_time)
VALUES ('/admin/profile', 'Admin Profile', '/admin/profile', 'Admin Profile', TRUE, current_timestamp);
INSERT INTO menu (value, display_value, url, description, is_active, last_update_time)
VALUES ('/user/dashboard', 'User Dashboard', '/user/dashboard', 'User Dashboard', TRUE, current_timestamp);
INSERT INTO menu (value, display_value, url, description, is_active, last_update_time)
VALUES ('/user/profile', 'User Profile', '/user/profile', 'User Profile', TRUE, current_timestamp);
- RoleMenuXref
CREATE TABLE role_menu_xref (
id INT NOT NULL AUTO_INCREMENT PRIMARY KEY,
role_id INT NOT NULL,
menu_id INT NOT NULL,
last_update_time TIMESTAMP DEFAULT current_timestamp ON UPDATE current_timestamp,
CONSTRAINT FOREIGN KEY fk_role_menu_xref_role_id (role_id) REFERENCES role (id),
CONSTRAINT FOREIGN KEY fk_role_menu_xref_menu_id(menu_id) REFERENCES menu (id),
CONSTRAINT UNIQUE (role_id, menu_id)
);
INSERT role_menu_xref (role_id, menu_id, last_update_time)
VALUES (1, 1, current_timestamp);
INSERT role_menu_xref (role_id, menu_id, last_update_time)
VALUES (1, 2, current_timestamp);
INSERT role_menu_xref (role_id, menu_id, last_update_time)
VALUES (2, 3, current_timestamp);
INSERT role_menu_xref (role_id, menu_id, last_update_time)
VALUES (2, 4, current_timestamp);
Collection 一个查询调用另一个查询实现的嵌套
<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"/>
<collection property="menus" ofType="cn.com.hellowood.springsecurity.model.menus"
javaType="java.util.ArrayList" select="getMenus"
column="id">
</collection>
</resultMap>
<resultMap id="BaseMenuResultMap" type="cn.com.hellowood.springsecurity.model.MenuModel">
<id column="id" property="id" jdbcType="INTEGER"/>
<result column="value" property="value" jdbcType="VARCHAR"/>
<result column="display_value" property="displayValue" jdbcType="VARCHAR"/>
<result column="url" property="url" jdbcType="VARCHAR"/>
<result column="category" property="category" jdbcType="INTEGER"/>
<result column="description" property="description" jdbcType="VARCHAR"/>
<result column="is_active" property="isActive" jdbcType="BIT"/>
<result column="last_update_time" property="lastUpdateTime" jdbcType="TIMESTAMP"/>
</resultMap>
<select id="getRoles" parameterType="java.lang.Integer" resultMap="BaseRoleResultMap">
SELECT
id,
name,
is_active,
description,
last_update_time
FROM role
</select>
<select id="getMenus" parameterType="java.lang.Integer" resultMap="BaseMenuResultMap">
SELECT
m.id,
m.value,
m.display_value,
m.url,
m.category,
m.description,
m.is_active,
m.last_update_time
FROM menu m
LEFT JOIN
role_menu_xref rmx
ON m.id = rmx.menu_id
WHERE role_id = #{roleId, jdbcType=INTEGER}
</select>
此时,调用
getRoles()
方法就可以通过嵌套查询同时查找 Role 属性了
<collection property="menus" ofType="cn.com.hellowood.springsecurity.model.menus"
javaType="java.util.ArrayList" select="getMenus"
column="id">
</collection>
- collection : 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 RoleModel 中对应
private List<MenuModel> menus;
- javaType : property 属性对应的集合类型
- ofType : property 集合中的泛型,在 RoleModel 中是 MenuModel
- column : RoleModel 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
Collection 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="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"/>
<collection property="menus" ofType="cn.com.hellowood.springsecurity.model.MenuModel"
javaType="java.util.ArrayList">
<id column="id" property="id" jdbcType="INTEGER"/>
<result column="value" property="value" jdbcType="VARCHAR"/>
<result column="display_value" property="displayValue" jdbcType="VARCHAR"/>
<result column="url" property="url" jdbcType="VARCHAR"/>
<result column="category" property="category" jdbcType="INTEGER"/>
<result column="description" property="description" jdbcType="VARCHAR"/>
<result column="is_active" property="isActive" jdbcType="BIT"/>
<result column="last_update_time" property="lastUpdateTime" jdbcType="TIMESTAMP"/>
</collection>
</resultMap>
<select id="getRoles" parameterType="java.lang.Integer" resultMap="BaseRoleResultMap">
SELECT
r.id,
r.name,
r.description,
r.is_active,
r.last_update_time,
m.id,
m.value,
m.display_value,
m.url,
m.category,
m.description,
m.is_active,
m.last_update_time
FROM role r
LEFT JOIN role_menu_xref rmx
ON r.id = rmx.role_id
LEFT JOIN menu m
ON m.id = rmx.menu_id
WHERE r.id = #{roleId,jdbcType=INTEGER}
</select>