Mybatis Plus 使用学习九 QueryWrapper使用上

QueryWrapper是一个优雅的条件拼装器，作用是构建where之后的查询条件。

1、多条件匹配查询，并且多个条件之间是AND的关系

相当于sql中的 where 列1= xxx and 列2= xxx

方法：

default <V> Children allEq(Map<R, V> params) {
        return allEq(params, true);
    }

代码：

    @Test
    public void testAllEq() {
        System.out.println(("----- allEq method test ------"));
        QueryWrapper wrapper = new QueryWrapper();
        Map<String,Object> map = new HashMap<>();
        map.put("Name", "Jack");
        map.put("Age", "20");
        wrapper.allEq(map);
        List<User> userList = userMapper.selectList(wrapper);
        userList.forEach(System.out::println);
    }

输出：

==>  Preparing: SELECT id,name,age,email FROM user WHERE (Age = ? AND Name = ?) 
==> Parameters: 20(String), Jack(String)
<==    Columns: ID, NAME, AGE, EMAIL
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1

User(id=2, name=Jack, age=20, email=test2@baomidou.com)

2、单个条件匹配查询，也就是指定一个字段和这个字段对应要匹配的值

相当于SQL的 where 列=xxx

方法：

default Children eq(R column, Object val) {
        return eq(true, column, val);
    }

代码：

    @Test
    public void testEq() {
        System.out.println(("----- eq method test ------"));
        QueryWrapper wrapper = new QueryWrapper();
        wrapper.eq("Name","Jack");
        List<User> userList = userMapper.selectList(wrapper);
        userList.forEach(System.out::println);
    }

输出：

==>  Preparing: SELECT id,name,age,email FROM user WHERE (Name = ?) 
==> Parameters: Jack(String)
<==    Columns: ID, NAME, AGE, EMAIL
<==        Row: 2, Jack, 20, test2@baomidou.com
<==      Total: 1

User(id=2, name=Jack, age=20, email=test2@baomidou.com)

3、不等于查询，也就是排除掉某写数据

相当于SQL中的 where 列 != xxx

也可以写成

where 列 <> xxx

方法：

default Children ne(R column, Object val) {
        return ne(true, column, val);
    }

代码：

    @Test
    public void testNe() {
        System.out.println(("----- eq method test ------"));
        QueryWrapper wrapper = new QueryWrapper();
        wrapper.ne("Name","Jack");
        List<User> userList = userMapper.selectList(wrapper);
        userList.forEach(System.out::println);
    }

输出：

==>  Preparing: SELECT id,name,age,email FROM user WHERE (Name <> ?) 
==> Parameters: Jack(String)
<==    Columns: ID, NAME, AGE, EMAIL
<==        Row: 1, Jone, 18, test1@baomidou.com
<==        Row: 3, Tom, 28, test3@baomidou.com
<==        Row: 4, Sandy, 21, test4@baomidou.com
<==        Row: 5, Billie, 24, test5@baomidou.com
<==      Total: 4

User(id=1, name=Jone, age=18, email=test1@baomidou.com)
User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)

4、大于操作

相当于SQL的 where 列 > xxx

方法：

default Children gt(R column, Object val) {
        return gt(true, column, val);
    }

代码：查询年龄大于22岁的

    @Test
    public void testGt() {
        System.out.println(("----- gt method test ------"));
        QueryWrapper wrapper = new QueryWrapper();
        wrapper.gt("Age","22");
        List<User> userList = userMapper.selectList(wrapper);
        userList.forEach(System.out::println);
    }

输出：

==>  Preparing: SELECT id,name,age,email FROM user WHERE (Age > ?) 
==> Parameters: 22(String)
<==    Columns: ID, NAME, AGE, EMAIL
<==        Row: 3, Tom, 28, test3@baomidou.com
<==        Row: 5, Billie, 24, test5@baomidou.com
<==      Total: 2

User(id=3, name=Tom, age=28, email=test3@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)

mybatis-plus还有相似的方法如 ge是大于等于，lt是小于，le是小于等于

5、配置一个有起始和结束区间的查询条件

SQL中的 between xxx and xxx

方法：

default Children between(R column, Object val1, Object val2) {
        return between(true, column, val1, val2);
    }

代码：

    @Test
    public void testBetween() {
        System.out.println(("----- between method test ------"));
        QueryWrapper wrapper = new QueryWrapper();
        wrapper.between("Age","21","25");
        List<User> userList = userMapper.selectList(wrapper);
        userList.forEach(System.out::println);
    }

输出：

==>  Preparing: SELECT id,name,age,email FROM user WHERE (Age BETWEEN ? AND ?) 
==> Parameters: 21(String), 25(String)
<==    Columns: ID, NAME, AGE, EMAIL
<==        Row: 4, Sandy, 21, test4@baomidou.com
<==        Row: 5, Billie, 24, test5@baomidou.com
<==      Total: 2

User(id=4, name=Sandy, age=21, email=test4@baomidou.com)
User(id=5, name=Billie, age=24, email=test5@baomidou.com)

还有与之相似的 notBetween方法。