JOOQ - Select Distinct with Join - Fetch mapper - sql

Question

This is the SQL I am trying to create with JOOQ -
select distinct(kmp.*) from office_all_company_kmp kmp
inner join company_kmp companykmp on kmp.id=companykmp.kmp_id
where companykmp.company_id=?1
I am writing code in Kotlin. I had 2 issues doing this -
In the select clause, unless I add a .asList() to the fields array, I couldn't get it compiling.
The fetch mapper had to be handcoded. Is there a way I can use do this without writing all that code? I can map records fetched back from one table without writing any mapping.
Here's what I am talking about:
fun OfficeAllCompanyKmpDao.findByCompany(companyId: UUID): List<OfficeAllCompanyKmp> =
this.ctx()
.selectDistinct(OFFICE_ALL_COMPANY_KMP.fields().asList()) // without the asList() it wouldn't compile
.from(OFFICE_ALL_COMPANY_KMP)
.join(COMPANY_KMP).on(OFFICE_ALL_COMPANY_KMP.ID.eq(COMPANY_KMP.KMP_ID))
.where(COMPANY_KMP.COMPANY_ID.eq(companyId))
.fetch { // how do I write the mapper without manually writing code like the below?
OfficeAllCompanyKmp(
id = it[OFFICE_ALL_COMPANY_KMP.ID],
officeId = it[OFFICE_ALL_COMPANY_KMP.OFFICE_ID],
din = it[OFFICE_ALL_COMPANY_KMP.DIN],
pan = it[OFFICE_ALL_COMPANY_KMP.PAN],
name = it[OFFICE_ALL_COMPANY_KMP.NAME],
dateOfBirth = it[OFFICE_ALL_COMPANY_KMP.DATE_OF_BIRTH],
address = it[OFFICE_ALL_COMPANY_KMP.ADDRESS],
email = it[OFFICE_ALL_COMPANY_KMP.EMAIL],
kmpDetails = it[OFFICE_ALL_COMPANY_KMP.KMP_DETAILS],
createdTimestamp = it[OFFICE_ALL_COMPANY_KMP.CREATED_TIMESTAMP],
updatedTimestamp = it[OFFICE_ALL_COMPANY_KMP.UPDATED_TIMESTAMP],
versionNo = it[OFFICE_ALL_COMPANY_KMP.VERSION_NO],
createdUserId = it[OFFICE_ALL_COMPANY_KMP.CREATED_USER_ID],
updatedUserId = it[OFFICE_ALL_COMPANY_KMP.UPDATED_USER_ID]
)
}

Answer 1

A better approach than inner joining and then removing duplicates again would be to semi join your other table using IN or EXISTS:
this.ctx()
.selectFrom(OFFICE_ALL_COMPANY_KMP)
.where(OFFICE_ALL_COMPANY_KMP.ID.`in`(
select(COMPANY_KMP.KMP_ID)
.from(COMPANY_KMP)
.where(COMPANY_KMP.COMPANY_ID.eq(companyId)))
.fetchInto(OfficeAllCompanyKmp::class.java)
Or, alternatively, use jOOQ's synthetic LEFT SEMI JOIN syntax (see also this blog post for an explanation for this syntax, or this one for joins in general, or Wikipedia's nice explanation about semi joins)
this.ctx()
.select()
.from(OFFICE_ALL_COMPANY_KMP)
.leftSemiJoin(COMPANY_KMP)
.on(OFFICE_ALL_COMPANY_KMP.ID.eq(COMPANY_KMP.KMP_ID))
.and(COMPANY_KMP.COMPANY_ID.eq(companyId))
.fetchInto(OfficeAllCompanyKmp::class.java)
Your problem 1) went away by using different jOOQ API, where you don't have to list all columns explicitly in SELECT. Your problem 2) is fixed easily by calling fetchInto() instead.