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From "Jonathan Hsieh (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HBASE-9142) Mutation#getFamilyMap() return type change between HBase 94 and 96 breaks downstream apps
Date Wed, 07 Aug 2013 20:51:48 GMT

    [ https://issues.apache.org/jira/browse/HBASE-9142?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13732716#comment-13732716
] 

Jonathan Hsieh commented on HBASE-9142:
---------------------------------------

First -- I think life is easier in you should probably create a new hbase95 sink. :) -- this
is a case where 0.94 didn't specify external visibility explictly yet and we didn't preserve
compat.

I added a method back and named the new method as getFamilyCellMap.  Along the way, I went
down the rathole of removing what I believe is a java collection of generics anti-pattern
along the way.  (which if it ends up being clean, we should get in to 0.95 before the api
freezes).  This may have been intentional by my gut says it should be removed.

Specifically it seems that defining this method with List<? extends Cell> where List<Cell>
is sufficient has caused superfluous casts and extra types to percolated throughout the code.
 Having gone through -client, -common, and -server, none of the uses of the List instances
require methods in Cell's implementor KeyValue that aren't in the Cell interface.  A List<Cell>
can hold KeyValue instances doesn't need have a List<KeyValue> type.  Since the maps
is essentially exposed and can be used for read/write access, it should be the collection
element typed should be typed invariantly. See [1] for short primer and examples. 

[1] http://en.wikipedia.org/wiki/Covariance_and_contravariance_(computer_science)

                
> Mutation#getFamilyMap() return type change between HBase 94 and 96 breaks downstream
apps
> -----------------------------------------------------------------------------------------
>
>                 Key: HBASE-9142
>                 URL: https://issues.apache.org/jira/browse/HBASE-9142
>             Project: HBase
>          Issue Type: Bug
>            Reporter: Hari Shreedharan
>            Assignee: Jonathan Hsieh
>            Priority: Critical
>             Fix For: 0.95.2
>
>
> In Hbase-94, Mutation#getFamilyMap() had signature:
> public Map<byte[],List<KeyValue>> getFamilyMap()
> In Hbase-96 it is:
> public NavigableMap<byte[],List<? extends Cell>> getFamilyMap()
> I understand this might not be an easy fix or even a possible one - but it breaks downstream
apps in a nasty way. If the app needs to process the individual columns, then the whole logic
is now different. Is there a way to work around this, if this cannot be fixed?

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