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From: ryaneleary <git@git.apache.org>
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Subject: [GitHub] accumulo pull request: ACCUMULO-2825 Add RowEncodingIterator
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Message-Id: <20140519204038.9F21A9360D1@tyr.zones.apache.org>
Date: Mon, 19 May 2014 20:40:38 +0000 (UTC)

Github user ryaneleary commented on the pull request:

    https://github.com/apache/accumulo/pull/7#issuecomment-43555087
  
    Sure. Here's an example of what I've done (by modifying the WholeRowIterator). Assume a table that contains 'documents' and various document information. Assume a table format like this (format: ```<row <cf : cq>> = value```):
    ```
    <docid1 <META : timestamp>> (long) 12345
    <docid1 <META : meta_field_1>> (String) metaFieldValue1
    <docid1 <META : meta_field_2>> (String) metaFieldValue2
    <docid2 <META : timestamp>>  (long) 23456
    ```
    
    For other reasons in the system, I have a protocol buffer definition that can be used for shipping this data around. It's definition looks like this:
    ```
    message DocumentMessage {
        optional int64 timestamp = 1;
        optional string meta_field_1 = 2;
        optional string meta_field_2 = 3;
    }
    ```
    
    I can define an iterator that is passed a generated protocol buffer class that can iterate over the whole row and automatically build the protocol buffer object. getTopValue() now returns a protocol buffer message that the application knows how to parse.
    
    This is nice for bulk loading and saves the client from having to build the message it would have had to build anyway. When iterating over the results returned by the scanner, an entire document at a time is returned instead of individual columns.
    
    I can provide a more concrete example/implementation of such a class if you'd like.


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