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From "Craig Russell (JIRA)" <derby-...@db.apache.org>
Subject [jira] Commented: (DERBY-1516) Inconsistent behavior for getBytes and getSubString for embedded versus network
Date Mon, 31 Jul 2006 21:55:14 GMT
    [ http://issues.apache.org/jira/browse/DERBY-1516?page=comments#action_12424673 ] 
            
Craig Russell commented on DERBY-1516:
--------------------------------------

Including the discussion from the alias referenced immediately above:

>> One interesting test with 0 length is the case for getSubString(1,0) 
>> for a zero length lob. 
>> Should it throw an exception or return a zero length string? 

>The API working doesn't give much help to resolve this; the wording for the exception
in JDK 1.6 is 

> Throws: 
>    SQLException - if there is an error accessing the CLOB value 

> which I guess is equivalent to YMMV... A case for Lance? 

> Even if this case is allowed, should it make a difference if position is > (length+1),
e.g. getSubString(2,0) for an empty CLOB? 

Lance has not replied to a request to update the wording, and I think time is running out
on this to be added to the specification in progress.

The jdbc spec has followed the java.lang.String spec pretty closely, modulo 1-origin vs. 0-origin
indexing. The String spec allows accessing substrings of a 0-length string, as follows:

public String substring(int beginIndex,
                        int endIndex)
Returns a new string that is a substring of this string. The substring begins at the specified
beginIndex and extends to the character at index endIndex - 1. Thus the length of the substring
is endIndex-beginIndex...
IndexOutOfBoundsException - if the beginIndex is negative, or endIndex is larger than the
length of this String object, or beginIndex is larger than endIndex.

For a zero-length String:
1. endIndex must be 0 or else endIndex would be larger than the length of the String;
2. beginIndex must be 0 or else beginIndex would be larger than endIndex.

Translating this to jdbc, for a zero-length Clob:
1. position must be 1;
2. length must be 0.

I agree we should add positive test cases to extract a zero-length substring from a Clob and
Blob. 

I propose adding to clobTest2 and blobTest2 a test like: 
blobclob4BLOB.printInterval(clob, 1, 0, 7, i, clobLength) // zero length
blobclob4BLOB.printInterval(blob, 1, 0, 7, i, blobLength) // zero length


> Inconsistent behavior for getBytes and getSubString for embedded versus network
> -------------------------------------------------------------------------------
>
>                 Key: DERBY-1516
>                 URL: http://issues.apache.org/jira/browse/DERBY-1516
>             Project: Derby
>          Issue Type: Bug
>          Components: JDBC
>            Reporter: Craig Russell
>         Assigned To: Craig Russell
>            Priority: Minor
>         Attachments: DERBY-1516.patch, DERBY-1516.patch, DERBY-1516.patch
>
>
> org.apache.derby.client.am.Clob.getSubString(pos, length) and org.apache.derby.client.am.Blob.getBytes(pos,
length) check the length for less than zero. 
>             if ((pos <= 0) || (length < 0)) {
>                 throw new SqlException(agent_.logWriter_, "Invalid position " + pos +
" or length " + length);
> But org.apache.derby.impl.jdbc.EmbedClob(pos, length) and org.apache.derby.impl.jdbc.EmbedBlob(pos,
length) check the length for less than or equal to zero.
>        if (length <= 0)
>             throw Util.generateCsSQLException(
>                 SQLState.BLOB_NONPOSITIVE_LENGTH, new Integer(length));
> The specification does not disallow length of zero, so zero length should be allowed.
I believe that the implementation in org.apache.derby.client.am is correct, and the implementation
in org.apache.derby.impl.jdbc is incorrect. 

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