分组

easy-query提供了方便的分组查询功能的支持

链式api

在entity模式下groupBy后会将多个结果集进行合并到group.groupTable()里面如果需要操作group前的表需要从group.groupTable()里面获取,当表达式是单表那么group.groupTable()本身就是当前表,当表达式是多表join的那么表达式的表访问存在于group.groupTable().t1....tn

方法	后续
groupBy(o->GroupKeys.of(o.column()))	group.groupTable()本身就是groupBy的入参o
groupBy((o1,o2)->GroupKeys.of(o1.column()))	group.groupTable().t1就是groupBy的入参o1 group.groupTable().t2就是groupBy的入参o2
groupBy((o1,o2,o3)->GroupKeys.of(o1.column()，o2.column()))	group.groupTable().t1就是groupBy的入参o1 group.groupTable().t2就是groupBy的入参o2 group.groupTable().t3就是groupBy的入参o3

参数前后变化
我们用一个简单的案例来描述一下java下面的stream api是如何变化的

public class Person {
        private String name;
        private String city;

        // 构造函数、getters & setters 省略
    }
List<Person> people = Arrays.asList(
                new Person("a", "e"),
                new Person("b", "f"),
                new Person("c", "g"),
                new Person("d", "h")
        );

        // 使用Stream API进行分组
        Map<String, List<Person>> groupedPeople = people.stream()
                                                      .collect(Collectors.groupingBy(Person::getCity));

        // 输出分组结果
        for (Map.Entry<String, List<Person>> entry : groupedPeople.entrySet()) {
            System.out.println("City: " + entry.getKey() + ", People: " + entry.getValue());
        }

说明!!!

groupBy后原先的List<Person> 变成了 Map<String, List<Person>>这个我们在表达式中称之为group感知在java层面基本上没有orm实现了这种效果(或者说极少一部分orm才有这个特性),
group感知有什么用,最重要的一点就是帮助用户了解数据结构的变化从而实现一个简易的防呆设计(除了group by的字段其余字段应该以聚合函数的形式出现在select里面)

对象模式

List<TopicGroupTestDTO> topicGroupTestDTOS = easyEntityQuery.queryable(Topic.class)
                .where(o -> o.id().eq("3"))
                //创建group by 2.3.4之前使用GroupKeys.TABLE1_10.of
                .groupBy(o -> GroupKeys.of(o.id()))
                .select(g->{
                    TopicGroupTestDTOProxy result = new TopicGroupTestDTOProxy();
                    result.id().set(g.key1());
                    result.idCount().set(g.intCount());
                    result.idMin().set(g.groupTable().id().min());
                    return result;
                })
                //.select(TopicGroupTestDTO.class,g -> Select.of(
                       //group.key1().as(TopicGroupTestDTO::getId),
                       //group.groupTable().id().intCount().as(TopicGroupTestDTO::getIdCount),
                       //group.groupTable().id().min().as(TopicGroupTestDTO::getIdMin)
                //))
                .toList();


==> Preparing: SELECT t.`id` AS `id`,COUNT(t.`id`) AS `id_count`,MIN(t.`id`) AS `id_min` FROM t_topic t WHERE t.`id` = ? GROUP BY t.`id`
==> Parameters: 3(String)
<== Total: 1

client模式

List<TopicGroupTestDTO> list = easyQueryClient.queryable(Topic.class)
        .where(t_topic -> t_topic.eq(TopicProxy.Fields.id, "3"))
        .groupBy(t_topic -> t_topic.column(TopicProxy.Fields.id))
        .select(TopicGroupTestDTO.class, t_topic -> t_topic.columnAs("id", "id").columnCountAs("id", "idCount"))
        .toList();


==> Preparing: SELECT t.`id` AS `id`,COUNT(t.`id`) AS `id_count` FROM t_topic t WHERE t.`id` = ? GROUP BY t.`id`
==> Parameters: 3(String)
<== Total: 1

EntityQuery group 多表2张表及以上,group.groupTable()无法表示为对应的表,需要通过group.groupTable().t1......t10来表示

List<BlogGroupIdAndName> list = easyEntityQuery.queryable(Topic.class)
                .leftJoin(BlogEntity.class, (t, b2) -> t.id().eq(b2.id()))
                .where((t, b2) -> {
                    t.title().isNotNull();
                    t.createTime().le(LocalDateTime.of(2021, 3, 4, 5, 6));
                })
                //创建group by 2.3.4之前使用GroupKeys.TABLE1_10.of
                .groupBy((t1, b2) -> GroupKeys.of(t1.id(), b2.star()))
                .select(group -> new BlogGroupIdAndNameProxy()
                    .id().set(group.key1())
                    .idCount().set(group.groupTable().t2.id().count())
                ).toList();

==> Preparing: SELECT t.`id` AS `id`,COUNT(t1.`id`) AS `id_count` FROM `t_topic` t LEFT JOIN `t_blog` t1 ON t1.`deleted` = ? AND t.`id` = t1.`id` WHERE t.`title` IS NOT NULL AND t.`create_time` <= ? GROUP BY t.`id`,t1.`star`
==> Parameters: false(Boolean),2021-03-04T05:06(LocalDateTime)
<== Time Elapsed: 7(ms)
<== Total: 0