Road SSM learning --Mybatis third day _ dynamic sql statement

A, where and if the label

1, the new method in the interface IUserDao

2, in the preparation of the corresponding content in IUserDao.xml

Here's ifthe inside testfor the conditional sentence, which the parameter names correspond java documents in the field instead of the database
ifcontent tag for splicing sql statement
in which wherethe label is actually where 1 = 1 is rewritten as select * from user

Note that when a plurality of particular iftime, since the label splice sql statement content, and so do not forget the following connection as
username like the userName} {# andSex = ...

<select id="findUserByCondition" resultMap="userMap" parameterType="user">
        select  * from user
        <where>
            <if test="userName != null and userName.length() > 0">
                username like #{userName}
            </if>
            <if test="userSex != null and userSex.length() > 0">
                and sex = #{userSex}
            </if>
        </where>
    </select>

ResultMap or mention above is:

<resultMap id="userMap" type="user">
        <id property="userId" column="id"></id>
        <result property="userName" column="username"></result>
        <result property="userBirthday" column="birthday"></result>
        <result property="userSex" column="sex"></result>
        <result property="userAddress" column="address"></result>
    </resultMap>

3. Writing Test Methods

public void testFindUserByCondition(){
        User user = new User();
        user.setUserName("%老新%");
        user.setUserSex("女");
        List<User> users = userDao.findUserByCondition(user);
        for (User u : users){
            System.out.println(u);
        }
    }

Two, foreach and sql tag

1, write methods IUserDao interface

Returns a List, transmission parameters for packaging entity QueryVo

2, adding QueryVo entity class field and get & set

Create a List, which are all id (s) you want to find

private List<Integer> ids = new ArrayList<Integer>();

public List<Integer> getIds() {
    return ids;
}

public void setIds(List<Integer> ids) {
    this.ids = ids;
}

3, write test classes

Create a List called IDS , this name is very important, it will be mentioned below
the rest see the comment on the line

public void testFindUserByIds(){
    List<Integer> ids = new ArrayList<Integer>();
    //创建一个vo
    QueryVo vo = new QueryVo();
    //往ids列表中添加要查找的id们
    ids.add(67);  
    ids.add(73);  
    ids.add(74);  
    //将ids传给vo实体类
    vo.setIds(ids);
    //产生结果List
    List<User> users = userDao.findUserByIds(vo);
    for (User user: users) {
        System.out.println(user);
    }
}

4, added in xml

Here the argument passed to a queryvo objects
ifin the teststill corresponds to the search criteria

Key :

<foreach>Tag inside of parameters:
Collection: object name need to pass a set of
open: conditions, attention followed by a left parenthesis (open parenthesis, so as Open)
Item: and the following contents #{id}in the id corresponding to
such item="id"correspondence #{id}, item="uid"correspondence #{uid}, as passed in alias parameters,
Close: close bracket, in conjunction with the open
separator: delimiter between a plurality of parameters sql statement, where a comma

<select id="findUserByIds" resultMap="userMap" parameterType="queryvo">
    select * from user
    <where>
        <if test="ids != null and ids.size() >0 ">
            <foreach collection="ids" open="and id in (" item="id" close=")" separator=",">
                #{id}
            </foreach>
        </if>
    </where>
</select>