CaseWhen

easy-query can implement custom case when, with the framework providing multiple default implementations:

Method	Description	Usage
SQLClientFunc	Supports EasyQueryClient expression API	SQLClientFunc.caseWhenBuilder(t).caseWhen(f -> f.eq("title", "123"), "111").caseWhen(f -> f.eq("title", "456"), "222").elseEnd("2223")
Expression	Supports EasyEntityQuery expression API	o.expression().caseWhen(() -> o.title().eq("123")).then("1").elseEnd("2")
Implicit CaseWhen	Use aggregate functions on properties + filter filtering	o.age().sum().filter(()->o.name().like("XiaoMing"))

Simple Query

entity

        easyEntityQuery.queryable(Topic.class)
                .where(t_topic -> {
                    t_topic.title().eq("someTitle");
                })
                .select(t_topic -> new TopicProxy()
                        .title().set(
                                t_topic.expression().caseWhen(() -> t_topic.title().eq("123")).then("1").elseEnd("2").asAnyType(String.class)
                        )
                        .id().set(t_topic.id())
                ).toList();

==> Preparing: SELECT (CASE WHEN t.`title` = ? THEN ? ELSE ? END) AS `title`,t.`id` AS `id` FROM `t_topic` t WHERE t.`title` = ?
==> Parameters: 123(String),1(String),2(String),someTitle(String)

client

List<Topic> list = easyQueryClient.queryable(Topic.class)
                .where(t -> t.like("title", "someTitle"))
                .select(Topic.class, t -> t
                        .sqlSegmentAs(
                                SQLClientFunc.caseWhenBuilder(t)
                                        .caseWhen(f -> f.eq("title", "123"), "111")
                                        .caseWhen(f -> f.eq("title", "456"), "222")
                                        .elseEnd("222")
                                , "title")
                        .column("id")
                ).toList();

==> Preparing: SELECT CASE WHEN t.`title` = ? THEN ? WHEN t.`title` = ? THEN ? ELSE ? END AS `title`,t.`id` FROM `t_topic` t WHERE t.`title` LIKE ?
==> Parameters: 123(String),111(String),456(String),222(String),222(String),%someTitle%(String)
<== Time Elapsed: 2(ms)
<== Total: 0

Multi-Condition CaseWhen

Sometimes our case when needs to implement multiple conditions rather than a single condition:

List<Topic> list = easyEntityQuery.queryable(Topic.class)
                .where(t_topic -> {
                    t_topic.expression().caseWhen(() -> t_topic.title().eq("123"))
                            .then(1)
                            .caseWhen(() -> {
                                t_topic.title().eq("456");
                                t_topic.stars().eq(1);
                            }).then(t_topic.stars())
                            .elseEnd(3).eq(4);
                    t_topic.title().eq("someTitle");
                })
                .select(t_topic -> new TopicProxy()
                        .title().set(
                                t_topic.expression().caseWhen(() -> t_topic.title().eq("123")).then("1").elseEnd("2").asAnyType(String.class)
                        )
                        .id().set(t_topic.id())
                ).toList();

==> Preparing: SELECT (CASE WHEN t.`title` = ? THEN ? ELSE ? END) AS `title`,t.`id` AS `id` FROM `t_topic` t WHERE (CASE WHEN t.`title` = ? THEN ? WHEN t.`title` = ? AND t.`stars` = ? THEN t.`stars` ELSE ? END) = ? AND t.`title` = ?
==> Parameters: 123(String),1(String),2(String),123(String),1(Integer),456(String),1(Integer),3(Integer),4(Integer),someTitle(String)
<== Time Elapsed: 2(ms)
<== Total: 0

Property Aggregate Function Filtering

eq implements implicit CaseWhen through property aggregate function filtering for most functions:

easyEntityQuery.queryable(BlogEntity.class)
        .where(t_blog -> {
                t_blog.title().like("123");

        }).groupBy(t_blog -> GroupKeys.of(t_blog.title()))
        .select(group -> Select.DRAFT.of(
                group.key1(),
                group.groupTable().id().count().filter(() -> {
                        group.groupTable().star().ge(123);
                })
        )).toList();



-- SQL 1
SELECT
    t.`title` AS `value1`,
    COUNT((CASE WHEN t.`star` >= 123 THEN t.`id` ELSE NULL END)) AS `value2` 
FROM
    `t_blog` t 
WHERE
    t.`deleted` = false 
    AND t.`title` LIKE '%123%' 
GROUP BY
    t.`title`

group+where

easyEntityQuery.queryable(BlogEntity.class)
        .where(t_blog -> {
                t_blog.title().like("123");

        }).groupBy(t_blog -> GroupKeys.of(t_blog.title()))
        .select(group -> Select.DRAFT.of(
                group.key1(),
                group.where(t -> t.star().ge(123)).count()
        )).toList();



-- SQL 1
SELECT
    t.`title` AS `value1`,
    COUNT((CASE WHEN t.`star` >= 123 THEN 1 ELSE NULL END)) AS `value2` 
FROM
    `t_blog` t 
WHERE
    t.`deleted` = false 
    AND t.`title` LIKE '%123%' 
GROUP BY
    t.`title`