[ad_1]
My goal is to have the ability to paginate a number of information at a time, say with every web page containing 4 information:
Web page 1:
Web page 2:
Web page 3:
Excessive-Degree Method
A excessive stage method to doing that is to introduce two parameters:
◉ Offset — the purpose from which to retrieve the information.
◉ Restrict — the variety of information to retrieve per web page
Restrict in all circumstances is 4 in my instance. Offset gives some technique to point out the place to retrieve the following set of information from. Bigtable orders the file lexicographically utilizing the important thing of every row, so one technique to point out offset is through the use of the important thing of the final file on a web page. Given this, and utilizing a marker offset of empty string for the primary web page, offset and file for every web page appears to be like like this:
Web page 1 — offset: “”, restrict: 4
Web page 2 — offset: “particular person#id-004”, restrict: 4
Web page 3 — offset: “particular person#id-008”, restrict: 4
The problem now could be in determining find out how to retrieve a set of information given a prefix, an offset, and a restrict.
Retrieving information given a prefix, offset, restrict
import com.google.cloud.bigtable.information.v2.BigtableDataClient
import com.google.cloud.bigtable.information.v2.fashions.Question
import com.google.cloud.bigtable.information.v2.fashions.Row
val rows: Checklist<Row> = bigtableDataClient.readRows(question).toList()
Now, Question has a variant that takes in a prefix and returns rows matching the prefix:
import com.google.cloud.bigtable.information.v2.BigtableDataClient
import com.google.cloud.bigtable.information.v2.fashions.Question
import com.google.cloud.bigtable.information.v2.fashions.Row
val question: Question = Question.create(“individuals”).restrict(restrict).prefix(keyPrefix)
val rows: Checklist<Row> = bigtableDataClient.readRows(question).toList()
This works for the primary web page, nonetheless, for subsequent pages, the offset must be accounted for.
A technique to get this to work is to make use of a Question that takes in a variety:
import com.google.cloud.bigtable.information.v2.BigtableDataClient
import com.google.cloud.bigtable.information.v2.fashions.Question
import com.google.cloud.bigtable.information.v2.fashions.Row
import com.google.cloud.bigtable.information.v2.fashions.Vary
val vary: Vary.ByteStringRange =
Vary.ByteStringRange
.unbounded()
.startOpen(offset)
.endOpen(finish)
val question: Question = Question.create(“individuals”)
.restrict(restrict)
.vary(vary)
The issue with that is to determine what the top of the vary must be. That is the place a neat utility that the Bigtable Java library gives is available in. This utility given a prefix of “abc”, calculates the top of the vary to be “abd”
import com.google.cloud.bigtable.information.v2.fashions.Vary
val vary = Vary.ByteStringRange.prefix(“abc”)
Placing this all collectively, a question that fetches paginated rows at an offset appears to be like like this:
val question: Question =
Question.create(“individuals”)
.restrict(restrict)
.vary(Vary.ByteStringRange
.prefix(keyPrefix)
.startOpen(offset))
val rows: Checklist<Row> = bigtableDataClient.readRows(question).toList()
When returning the consequence, the ultimate key must be returned in order that it may be used because the offset for the following web page, this may be executed in Kotlin by having the next kind:
information class Web page<T>(val information; Checklist<T>, val nextOffset: String)
Supply: javacodegeeks.com
[ad_2]
