Pagination

[Dark-Knight11]

Hi, I was referring this project to implement pagination in my own project. I wanted to ask is there anyway to merge the count and data fetching queries.

maadb-project/nosql-analytics-server/src/main/kotlin/edu/unito/maadb/analytics/nosql/Datasource.kt

Lines 105 to 121 in 297ba70

	override suspend fun tweets(
	sentiment: SpecificSentiment,
	page: Int,
	pageSize: Int
	): PagedData<List<ElaboratedTweet>> = coroutineScope {
	val totalPages = async {
	ceil(tweetsCollection.countDocuments("{sentiment: \"$sentiment\"}") / pageSize.toFloat())
	.toInt()
	}
	val data = async {
	tweetsCollection.find("{sentiment: \"$sentiment\"}")
	.skip(page * pageSize)
	.limit(pageSize)
	.toList()
	}
	PagedData(data.await(), page, pageSize, totalPages.await())
	}

Here you are traversing the tweetsCollection 2 times - once for the total pages count and another time for fetching data. Is there anyway to do it in single query.

I tried this but it isn't working

val result = transactions.aggregate<Test>(
    facet(
        Facet("count",
            count()
        ),
        Facet(
            "transactions", listOf(
                skip((pageNo - 1) * size),
                limit(size)
            )
        )
    )
).first()
println(result.transactions)
println(result.count)

data class Test(val count: Long, val transactions: List<Transaction>?)

I get this error

Cannot deserialize value of type `long` from Array value (token `JsonToken.START_ARRAY`)\n at [Source: de.undercouch.bson4jackson.io.LittleEndianInputStream@11c18e82; pos: 7] (through reference chain: TransactionRepository$Test[\"count\"])

you have any idea on it?