一文掌握MyBatis?Plus的條件構(gòu)造器方法

更新時(shí)間：2023年02月09日 08:08:15 作者：世界盡頭與你

這篇文章主要介紹了MyBatis?Plus的條件構(gòu)造器,本文通過實(shí)例代碼給大家介紹的非常詳細(xì)，對(duì)大家的學(xué)習(xí)或工作具有一定的參考借鑒價(jià)值，需要的朋友可以參考下

1.組裝查詢條件

組裝查詢其實(shí)很簡(jiǎn)單，可以支持條件的鏈?zhǔn)骄幊蹋?/p>

查詢用戶名包含a，年齡在 10 - 20 之間并且郵箱不為空的用戶：

@Test
void contextLoads() {
    // 查詢用戶名包含a，年齡在 10 - 20 之間并且郵箱不為空的用戶
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.like("name","a")
            .between("age",10,20)
            .isNotNull("email");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (name LIKE ? AND age BETWEEN ? AND ? AND email IS NOT NULL)
==> Parameters: %a%(String), 10(Integer), 20(Integer)
<==    Columns: id, name, age, email, is_delete
<==        Row: 2, dada, 11, 111@qq.com, 0
<==        Row: 4, dahe, 12, 34567@qq.com, 0
<==      Total: 2

2.組裝排序條件

查詢用戶信息，按照年齡的降序排序，若年齡相同，則按照id升序排序：

@Test
void contextLoads() {
    // 查詢用戶信息，按照年齡的降序排序，若年齡相同，則按照id升序排序
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.orderByDesc("age").orderByAsc("id");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 ORDER BY age DESC,id ASC
==> Parameters: 
<==    Columns: id, name, age, email, is_delete
<==        Row: 3, dahe, 33, 34567@qq.com, 0
<==        Row: 4, dahe, 12, 34567@qq.com, 0
<==        Row: 2, dada, 11, 111@qq.com, 0
<==      Total: 3

3.使用Lambda表達(dá)式解決條件優(yōu)先級(jí)

將用戶名中包含有a并且（年齡大于20或郵箱為null）的用戶信息查詢出來：

Lambda中的條件優(yōu)先執(zhí)行！

@Test
void contextLoads() {
    // 將用戶名中包含有a并且（年齡大于20或郵箱為null）的用戶信息查詢出來
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.like("name", "a")
            .and(i -> i.gt("age", 20).or().isNull("email"));
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (name LIKE ? AND (age > ? OR email IS NULL))
==> Parameters: %a%(String), 20(Integer)
<==    Columns: id, name, age, email, is_delete
<==        Row: 3, dahe, 33, 34567@qq.com, 0
<==      Total: 1

4.組裝select語(yǔ)句

有時(shí)我們不想查詢數(shù)據(jù)庫(kù)某張表的所有字段，可以使用maps集合選擇只查詢某些字段的值：

@Test
void contextLoads() {
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.select("name","email");
    List<Map<String, Object>> maps = userMapper.selectMaps(wrapper);
    maps.forEach(System.out::println);
}

==>  Preparing: SELECT name,email FROM user WHERE is_delete=0
==> Parameters: 
<==    Columns: name, email
<==        Row: dada, 111@qq.com
<==        Row: dahe, 34567@qq.com
<==        Row: dahe, 34567@qq.com
<==      Total: 3
Closing non transactional SqlSession [org.apache.ibatis.session.defaults.DefaultSqlSession@237add]
{name=dada, email=111@qq.com}
{name=dahe, email=34567@qq.com}
{name=dahe, email=34567@qq.com}

5.組裝子查詢

@Test
void contextLoads() {
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.inSql("id","select id from user where id > 1");
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (id IN (select id from user where id > 1))
==> Parameters: 
<==    Columns: id, name, age, email, is_delete
<==        Row: 2, dada, 11, 111@qq.com, 0
<==        Row: 3, dahe, 33, 34567@qq.com, 0
<==        Row: 4, dahe, 12, 34567@qq.com, 0
<==      Total: 3

6.使用UpdateWrapper實(shí)現(xiàn)修改功能

將名字中包含a的記錄修改：

@Test
void contextLoads() {
    // 將名字中包含a的記錄修改
    UpdateWrapper<User> wrapper = new UpdateWrapper<>();
    wrapper.like("name","a");
    wrapper.set("name","hello").set("age",18);
    userMapper.update(null, wrapper);
}

JDBC Connection [com.mysql.cj.jdbc.ConnectionImpl@36c07c75] will not be managed by Spring
==>  Preparing: UPDATE user SET name=?,age=? WHERE is_delete=0 AND (name LIKE ?)
==> Parameters: hello(String), 18(Integer), %a%(String)
<==    Updates: 3

7.模擬開發(fā)中組裝條件的情況

真實(shí)的開發(fā)中往往有這樣的情況：我們不知道前端傳來的條件是什么，此時(shí)無(wú)法正常的拼接sql，那么就需要在后端進(jìn)行相應(yīng)的判斷：

@Test
 void contextLoads() {
     String name = null;
     Integer ageBegin = 18;
     Integer ageEnd = 28;
     QueryWrapper<User> wrapper = new QueryWrapper<>();
     if (StringUtils.isNotBlank(name)) {
         wrapper.like("name", name);
     }
     if (ageBegin != null) {
         wrapper.ge("age", ageBegin);
     }
     if (ageEnd != null) {
         wrapper.le("age", ageEnd);
     }
     List<User> users = userMapper.selectList(wrapper);
     users.forEach(System.out::println);
 }

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (age >= ? AND age <= ?)
==> Parameters: 18(Integer), 28(Integer)
<==    Columns: id, name, age, email, is_delete
<==        Row: 3, hello, 18, 34567@qq.com, 0
<==        Row: 4, hello, 18, 34567@qq.com, 0
<==      Total: 2

但是，這樣的判斷我們認(rèn)為過于的簡(jiǎn)陋和復(fù)雜，事實(shí)上，MyBatis Plus的條件構(gòu)造器中為我們封裝了解決此類問題的一些重載方法：

@Test
void contextLoads() {
    String name = null;
    Integer ageBegin = 18;
    Integer ageEnd = 28;
    QueryWrapper<User> wrapper = new QueryWrapper<>();
    wrapper.like(StringUtils.isNotBlank(name), "name", name);
    wrapper.ge(ageBegin != null, "age", ageBegin);
    wrapper.le(ageEnd != null, "age", ageEnd);
    List<User> users = userMapper.selectList(wrapper);
    users.forEach(System.out::println);
}

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (age >= ? AND age <= ?)
==> Parameters: 18(Integer), 28(Integer)
<==    Columns: id, name, age, email, is_delete
<==        Row: 3, hello, 18, 34567@qq.com, 0
<==        Row: 4, hello, 18, 34567@qq.com, 0
<==      Total: 2

8.LambdaQueryWrapper和LambdaUpdateWrapper

使用LambdaQueryWrapper和LambdaUpdateWrapper可以防止我們的字段名修改導(dǎo)致的程序錯(cuò)誤或字段名寫錯(cuò)

例如：

@Test
 void contextLoads() {
     String name = null;
     Integer ageBegin = 18;
     Integer ageEnd = 28;
     LambdaQueryWrapper<User> wrapper = new LambdaQueryWrapper<>();
     wrapper.like(StringUtils.isNotBlank(name), User::getName, name);
     wrapper.ge(ageBegin != null, User::getAge, ageBegin);
     wrapper.le(ageEnd != null, User::getAge, ageEnd);
     List<User> users = userMapper.selectList(wrapper);
     users.forEach(System.out::println);
 }

==>  Preparing: SELECT id,name,age,email,is_delete FROM user WHERE is_delete=0 AND (age >= ? AND age <= ?)
==> Parameters: 18(Integer), 28(Integer)
<==    Columns: id, name, age, email, is_delete
<==        Row: 3, hello, 18, 34567@qq.com, 0
<==        Row: 4, hello, 18, 34567@qq.com, 0
<==      Total: 2

LambdaUpdateWrapper的使用方法類似

到此這篇關(guān)于MyBatis Plus的條件構(gòu)造器的文章就介紹到這了,更多相關(guān)MyBatis Plus的條件構(gòu)造器內(nèi)容請(qǐng)搜索腳本之家以前的文章或繼續(xù)瀏覽下面的相關(guān)文章希望大家以后多多支持腳本之家！

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