How to Map One-To-Many Relation to JSON Model in Slick - json

Question

I have 2 classes like this
case class Employee(id: Long,
name: String,
prefix: Option[String],
role: String)
case class Report(id: Long,
name: String,
employee_id: Long)
expecting JSON format
{
"id":1,
"name":"employee",
"prefix":"emp",
"role":"eng",
"reports":[
{
"id":1,
"name":"report_1"
},
{
"id":2,
"name":"report_2"
}
]
}
an employee can have many reports (one-to-many) and i have tables connected with foreign key my questions in which way to retrieve data from database i tried inner join like this
val query: PostgresProfile.api.type#TableQuery[T]
def getAllQuery = {
query.filter(_.isDeleted === false)
}
================================================
def getAllEmployee: Future[Seq[Employee]] = {
val joinQuery = super.getAllQuery.join(reportRepo.getAllQuery).on(_.id === _.employee_id)
val joinRes: Future[Seq[(Employee, Report)]] = db.run(joinQuery.result)
joinRes map { tupleList =>
tupleList.map { tuple =>
Employee(tuple._1.id, tuple._1.name, tuple._1.prefix, tuple._1.role)
}
}
}
i received the data and when i tried to map to JSON it comes with duplicate values too. can anyone suggest way to map or better way to retrieve data from DB with an example.
sorry if i made any mistakes i'm new to playframework and thanks is advance.

Answer 1

The thing which you are looking is groupBy, I guess.
You fetch the data by your join query and groupBy on the employee's ID.
val query = employee.filter(_.yourField === yourCondition).join(report).on(_.id === _.employee_id)
val joinRes = db.run(query.to[List].result)
joinRes.map { list =>
list.groupBy {
case (emp, report) => emp.id
}
}
or
joinRes.map(_.groupBy(_._1.id))
Now
where employee is TableQuery object of employee and report is TableQuery object of report.
Give it a try :)

Answer 2

To get desired json you need to map result into appropriate case class.
case class EmployeeWithReports(id: Long,
name: String,
prefix: Option[String],
role: String,
reports: List[Report])
object EmployeeWithReports {
implicit val jsonFormat = Json.format[EmployeeWithReports]
}
Mapping to this case class can be done in DBIOAction. Firstly group result by employee id and than map all map entries (Int, Seq[Employee, Report]) to EmployeeWithReports
val query = super.getAllQuery
.join(reportRepo.getAllQuery)
.on(_.id === _.employee_id)
val action = query.result.map(rows => {
rows.groupBy(_._1.id).map { mapEntry =>
val (id, name, prefix, role) = mapEntry._2.head._1
EmployeeWithReports(id, name, prefix, role, mapEntry._2.flatMap(_._2).toList)
}.toList
})
Then you can get result calling
val employees: Future[List[EmployeeWithReports]] = db.run(action)