Not exactly sure what you're trying to do.  You can easily generate a number 
when you index each Document and insert it in a uid field (which is, BTW, what 
I do), and if you base it on a timestamp plus some characteristic of the 
document (which is also what I do), it should always be unique.  As you add 
more documents, they will each get their own unique id.  When you delete 
documents and optimize, these ids won't be affected.

However, in your subsequent clarification, you indicated you already had a 
unique id, and want to find the maximum value.  So why did you say you want one 

  ----- Original Message ----- 
  From: aurora 
  Sent: Monday, November 22, 2004 4:39 PM
  Subject: Re: auto-generate uid?

  Just to clarify. I have a Field 'uid' those value is an unique integer. I  
  use it as a key to the document stored externally. I don't mean Lucene's  
  internal document number.

  I was wonder if there is a method to query the highest value of a field,  
  perhaps something like:


  > What would the purpose of an auto-generated UID be?
  > But no, Lucene does not generate UID's for you.  Documents are numbered  
  > internally by their insertion order.  This number changes, however, when  
  > documents are deleted in the middle and the index is optimized.
  > Erik
  > On Nov 22, 2004, at 1:50 PM, aurora wrote:
  >> Is there a way to auto-generate uid in Lucene? Even it is just a way to  
  >> query the highest uid and let the application add one to it will do.
  >> Thanks.
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