Joining a last activity record

I’ve following two entities where I’m trying to get the latest activity for an employee:

interface Activity : Entity<Activity> {
    val id: Long
    val desc: String
    val employee: Employee
    val createdAt: LocalDateTime?
    companion object : Entity.Factory<Activity>()
}

interface Employee : Entity<Employee> {
    var id: Long
    var name: String
    
    val latestActivity: Activity?
        get() {
            var activity = this["latestActivity"]
            if (activity == null) {
                activity = Activities.asSequenceWithoutReferences().sortedByDescending { it.createdAt }
                    .filter { it.employeeId eq id }.firstOrNull()
                this["latestActivity"] = activity
            }
            return activity as? Activity
        }
    companion object : Entity.Factory<Employee>()
}

This all works great but unfortunately for each employee getting the latestActivity is an extra query. What’s the best way to fetch Employees and have it returned with latestActivity joined?

[vincentlauvlwj]

I also tried to use a native SQL. In this way, only one query is executed:

val employees = useConnection { conn ->
    val sql = """
        select emp.id as emp_id, emp.name as emp_name, act.id as act_id, act.desc as act_desc, act.created_at as act_time
        from employee emp left join (
            select a.id, a.employee_id, a.desc, a.created_at
            from activity a
            where a.id = (
                select max(b.id)
                from activity b
                where b.employee_id = a.employee_id
            )
        ) act on emp.id = act.employee_id;
    """.trimIndent()

    conn.prepareStatement(sql).use { statement ->
        statement.executeQuery().use { rs ->
            rs.iterable().map { row ->
                Employee {
                    id = row.getLong("emp_id")
                    name = row.getString("emp_name")
                    latestActivity = Activity {
                        id = row.getLong("act_id")
                        desc = row.getString("act_desc")
                        createdAt = row.getTimestamp("act_time")?.toLocalDateTime()
                    }
                }
            }
        }
    }
}

[ashokgelal]

Great! I would be very happy to test it out on a real database once ready. Any idea about when it might be available?