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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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