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Custom Flat Object

xuejmnet5/5/25About 4 min

Assignment Types

eq has two main types of common assignments:

    1. Implicit assignment .select(DTO.class): Fields are mapped based on conventions between field names and DTO field names. See Object Mapping DTO Rules for details.
    1. Explicit assignment: As the name suggests, assigning values to receiving results through explicit programming methods.

Explicit Assignment

eq's implicit assignment is relatively simple and won't be discussed in detail here. This chapter mainly describes explicit assignment.

Proxy Assignment

Requires adding @EntityProxy annotation to DTO, then return the corresponding proxy object when selecting, for example return new DTOProxy(), and set properties in the select method.

Return DTO:

@Data
@EntityProxy
public class GenericDTO {
    private String value1;
    private String value2;
}

        List<GenericDTO> list1 = easyEntityQuery.queryable(SysUser.class)
                .where(s -> {
                    s.phone().startsWith("186");
                })
                .select(s -> new GenericDTOProxy()
                        .value1().set(s.phone())
                        .value2().set(s.address().subString(1, 10))
                ).toList();


    SELECT
        t.`phone` AS `value1`,
        SUBSTR(t.`address`, 2, 10) AS `value2` 
    FROM
        `easy-query-test`.`t_sys_user` t 
    WHERE
        t.`phone` LIKE CONCAT('186', '%')

Generic Proxy Assignment

No need to add extra processing to DTO, no need to add @EntityProxy, directly use new ClassProxy(DTO.class) to return results.

ClassProxy is a generic class object mapping builder. Users who don't want to add @EntityProxy but want chain style can choose this method.

Return DTO:

@Data
public class GenericDTO {
    private String value1;
    private String value2;
}


        List<GenericDTO> list1 = easyEntityQuery.queryable(SysUser.class)
                .where(s -> {
                    s.phone().startsWith("186");
                })
                .select(s -> new ClassProxy<>(GenericDTO.class)
                    //.selectAll(s)//If need full field mapping
                    .field("value1").set(s.phone())
                    .field("value2").set(s.address().subString(1, 10))
                ).toList();


    SELECT
        t.`phone` AS `value1`,
        SUBSTR(t.`address`, 2, 10) AS `value2` 
    FROM
        `easy-query-test`.`t_sys_user` t 
    WHERE
        t.`phone` LIKE CONCAT('186', '%')

If you don't want to use strings value1 and value2 as as parameters, you can also use lombok's another annotation @FieldNameConstants or method reference GenericDTO::getValue1 (method reference requires property name to be standard Java bean property name).

Return DTO:

@Data
@FieldNameConstants
public class GenericDTO {
    private String value1;
    private String value2;
}

Use GenericDTO.Fields.value1 to achieve static compile-time constant usage and ensure strong-typed as:



        List<GenericDTO> list1 = easyEntityQuery.queryable(SysUser.class)
                .where(s -> {
                    s.phone().startsWith("186");
                })
                .select(s -> new ClassProxy<>(GenericDTO.class)
                    //.selectAll(s)//If need full field mapping
                    .field(GenericDTO.Fields.value1).set(s.phone())
                    .field(GenericDTO.Fields.value2).set(s.address().subString(1, 10))
                ).toList();


    SELECT
        t.`phone` AS `value1`,
        SUBSTR(t.`address`, 2, 10) AS `value2` 
    FROM
        `easy-query-test`.`t_sys_user` t 
    WHERE
        t.`phone` LIKE CONCAT('186', '%')

Custom DTO, VO Return Results

Sometimes we want to directly return database query result objects as objects we need, instead of first querying database objects and then converting them in memory to objects we need. For example, after joining two tables, we want to return select a.id,b.name from a join b ..., then we will choose to create an object to receive the database return results.

Multi-Table Return Expression

Explicit Assignment 1
//
easyEntityQuery
        .queryable(Topic.class)
        .leftJoin(BlogEntity.class, (t,t1) -> t.id().eq(t1.id()))
        .leftJoin(SysUser.class, (t,t1,t2) -> t.id().eq(t2.id()))
        .where((t,t1,t2) -> {
                t.id().eq("123");
                t1.title().like("456");
                t2.createTime().eq(LocalDateTime.now());
        })
        //If don't want to use chain style brace method, execution order is code order, default use and to link
        //Dynamic expression
        .where(o -> {
            o.id().eq("1234");
            if (true) {
                o.id().eq("1234");//false means don't use this condition
            }
            o.id().eq(true,"1234");//false means don't use this condition

        })
        .select((t,t1,t2) -> new TopicTypeVOProxy()
                .id().set(t2.id())
                .title().set(t1.title())
                .createTime().set(t2.createTime())
        );

Multi-Table Custom Result API

Object Mode

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