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From: Adrien Grand <jpountz@gmail.com>
Date: Thu, 4 Apr 2013 20:22:43 +0200
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 <CAPsWd+M_m_E4vuS=tx9NvpucUMqm8ewd3MNK0pbCjkgrX6KEcA@mail.gmail.com>
Subject: Re: DocValues questions
To: java-user@lucene.apache.org
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Hi,

On Thu, Apr 4, 2013 at 10:30 AM, Wei Wang <welshwang@gmail.com> wrote:
> A few quick questions about DocValues:
>
> 1. If only small number of documents have a ShortDocValueField defined,
> should each document in the index has this field filled with some value?
> The add() function of Document seems not enforce a DocValues field is
> always added to each document.

Given the name of the fied you are referring to, I assume that you are
using Lucene 4.0 or 4.1. I would highly recommend to upgrade to Lucene
4.2 since the API has been completely refactored (but the disk format
is compatible) and should hopefully be a little clearer.

You are right that there is nothing that enforces that every document
has a value : Lucene will give a default value to documents: 0 for
numeric doc values and an empty byte array for binary doc values.

> 2. Is there any examples to show how DocValues are stored and retrieved? It
> seems JavaDoc only shows how to add it, and no complete examples are out
> there.

This should be transparent if you use doc values for eg. sorting.
Otherwise, just call getNumericDocValues(field), getBinaryDocValues or
getSortedDocValues on an AtomicReader.

I hope this helps.

--
Adrien

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