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From "Alfonso Nishikawa (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (GORA-195) [gora-hbase] Allow mapping of an array to a single column
Date Fri, 04 Jan 2013 23:04:12 GMT

    [ https://issues.apache.org/jira/browse/GORA-195?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13544332#comment-13544332
] 

Alfonso Nishikawa commented on GORA-195:
----------------------------------------

Hi, Renato. Don't worry. Sorry for how badly I explain myself.
HBase at this moment recomends using only a few families (column families) as stated in it's
documentation [0]. This is not bad. To achieve that, one way is map(.xml) "maps" and "arrays"
to a family:column. In some cases this could be beneficial.

But in Gora+HBase you can't do this. You can only map(.xml) "maps" and "arrays" to families,
so you are forced to create a family for each map/array.

About the "unexpected behaviour", at this state, if you configure your mapping(.xml) to map(.xml)
"map" or "array" to a family:column, you don't get an exception, nor a config error, nor nothing.
All works, but the data you get when you read one of this fields is trash. I wanted to notice
it as a warning, since maybe all seems to work fine until you examine your data.

Thanks for asking for a clarification :)

[0] - http://hbase.apache.org/book/number.of.cfs.html
                
> [gora-hbase] Allow mapping of an array to a single column
> ---------------------------------------------------------
>
>                 Key: GORA-195
>                 URL: https://issues.apache.org/jira/browse/GORA-195
>             Project: Apache Gora
>          Issue Type: Improvement
>          Components: storage-hbase
>    Affects Versions: 0.2.1
>         Environment: HBase 0.90.4 backend, Hadoop 1.0.1
>            Reporter: Alfonso Nishikawa
>            Priority: Trivial
>
> At this time, defining a mapping in HBase for an array field to a family:column like
this:
> {code}
> {"name": "A",
>  "fields": [
>         {"name": "field",  "type": {"type": "array", "values": "string"}}
>    ]
> }
> <class name="A" ...>
>   <field name="field" family="r" qualifier="c"/>
> </class>
> {code}
> in HBase is discouraging since gets to an unexpected behavior loading parts of the rest
of the record.
> So: by now only is allowed mappings of arrays(and maps) to families.
> Workaround: enclose the array inside an inner optional record like this:
> {code}
> {"name": "A",
>  "fields": [
>         {"name":"holder", "type:" ["null", {
>                     "name":"holderRecord",
>                     "type":"record",
>                     "fields": [
>                          {"name": "field",  "type": {"type": "array", "values": "string"}}
>                      ]
>         }}
>    ]
> }
> {code}
> The necessity comes partially if you don't want to create a family for each array in
you HBase database (advised not to do), or if you just want to map to a column when your array
is read-only.

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