Create Single from other singles and completable

Question

I have a repository that returns Single<List<Table>>. This repository calls a datasource that creates a network call to return these objects from somewhere else (datasource returns Single<List<Table>>) . Once this data is acquired I need to make a local query to compare with the local database on a 1 to 1 basis (for each Table a new local query needs to be consulted and the original Table will change, local query returns Single<Table>). Once that item has changed I need to save it locally (it returns Completable). And once that is done I need to return this changed Single<List<Table>>

TLDR:

• Get list from server Single<List<Table>>
• loop each item from that list
• for each item check something in local database(local db returns Single<Table>)
• change original item based on local database
• save that changed item into local db, returns Completable
• return changed list Single<List<Table>>

This is the code I got

fun getTables(param1: String): Single<List<Table> {
    remoteDataSource.getRemoteTables()
        .map { tables ->
            tables.map { table ->
                localDatasource.findById(table.id)
                    .subscribe({
                       val newTable = Table(table.id, it.name)
                       localDatasource.save(newTable)
                       //and here is when I realized I don't like rxjava.
                     },{})

            }
        }
}

I have no idea how to make this. Any help will be apreciated.

Answer 1

You can use a set of flatMap operators:

remoteDataSource.getRemoteTables()
.flattenAsFlowable { it }
.flatMapSingle { table ->
    localDatasource.findById(table.id)
    .flatMapCompletable { table2 ->
         val newTable = Table(table.id, table2.name)
         localDatasource.save(newTable)
    }
    .toSingleDefault(table)
}
.toList()