Java 中使用Linq

　maven安装。

<dependency>
    <groupId>com.bestvike</groupId>
    <artifactId>linq</artifactId>
    <version>3.1.0</version>
</dependency>

带where查询

//方法链
var ddd = Linq.of(list).where(x -> x.getAge() > 15).toList();

//sql
String sql = "select * from user where age>15";

　　简单的函数计算（max、min、count、sum）

//方法链
//var ddd = Linq.of(list).max(x -> x.getAge());//获取最大的年龄
//var ddd = Linq.of(list).min(x -> x.getAge());//获取最小的年龄
//var ddd = Linq.of(list).count();//获取总数
var ddd = Linq.of(list).sumInt(x -> x.getAge());//获取总数

//sql
//String sql = "select max(age) from user";
//String sql = "select min(age) from user";
//String sql = "select count(1) from user";
String sql = "select sum(age) from user";

　　排序

//方法链
//var ddd = Linq.of(list).orderBy(x -> x.getAge());//正序
var ddd = Linq.of(list).orderByDescending(x -> x.getAge());//倒序

//sql
//String sql = "select * from user order by age";
String sql = "select * from user order by age desc";

　　top1

//方法链
var ddd = Linq.of(list).firstOrDefault();

//sql
String sql = "select top 1 from user";

 　　跳过前面多少条数据，取剩下的数据

//方法链
var ddd = Linq.of(list).orderByDescending(x -> x.getAge()).skip(1);

//sql
String sql = "select * from (select ROW_NUMBER() over(order by age desc) as rowNum,*) t wher rowNum>1";

　　分页查询

//方法链
//跳过第一条，取两条，即取第二条到第四条
var ddd = Linq.of(list).orderByDescending(x -> x.getAge()).skip(1).take(3);

//sql
String sql = "select * from (select ROW_NUMBER() over(order by age desc) as rowNum,*) t wher rowNum>1 and rowNum<=4";

　　包含，相当于like

//方法链
var ddd = Linq.of(list).where(x->x.getName().contains("李"));

//sql
String sql = "select * from user where name like '%李%'";

　　分组group by

//方法链
var ddd = Linq.of(list).groupBy(x -> x.getAge()).toList();
for (var t : ddd) {
    System.out.println(t.getKey() + "--" + t.minInt(x -> x.getMoney()) + "--" + t.maxInt(x -> x.getMoney()) + "--" + t.sumInt(x -> x.getMoney()));
}

//sql
String sql = "select age,min(money),max(money),sum(money) from user group by age";

　　sql中的in

//方法链
List<Integer> ages = new ArrayList<>();
ages.add(15);
ages.add(16);
var ddd = Linq.of(list).where(x -> ages.contains(x.getAge()));

//sql
String sql = "select * from user where age in (15,16)";