Trim on a clob returns ORA-22926 if the clob is the result of getClobVal()

Question

I tried to trim whitespace from a CLOB, and got an ORA-22926 exception, which is strange since I did not supply a trim length. I eventually noticed that it only occurs when the CLOB is the result of the getClobVal method. The following code triggers the exception:
declare
  v_clob clob;
  v_xml xmltype;
  i pls_integer;
begin
  v_clob := '<node>test</node>';
  i := 0;
  loop
    exit when i > 12;
    v_clob := v_clob || v_clob;
    i := i + 1;
  end loop;
  v_clob := '<root>' || v_clob || '</root>';
  v_xml := xmltype(v_clob);
  v_clob := v_xml.getClobVal();
  v_clob := trim(v_clob);
end;
/ORA-22926: specified trim length is greater than current LOB value's length
ORA-06512: at line 17
Note that the exception is not triggered when the line v_clob := v_xml.getClobVal(); is removed. Any ideas why this exception occurs?
Oracle version is Oracle Database 11g Enterprise Edition Release 11.1.0.6.0 .

Answer 1

And looking at your original example if you use XMLSERIALIZE rather than the depricated getClobVal() method the problem you descibe goes away..
SQL> declare
  2    v_clob clob;
  3    v_xml xmltype;
  4    i pls_integer;
  5  begin
  6    v_clob := '<node>test</node>';
  7    i := 0;
  8    loop
  9      exit when i > 12;
10      v_clob := v_clob || v_clob;
11      i := i + 1;
12    end loop;
13    v_clob := '<root>' || v_clob || '</root>';
14    v_xml := xmltype(v_clob);
15    v_clob := v_xml.getCLobVal();
16    v_clob := trim(v_clob);
17  end;
18  /
declare
ERROR at line 1:
ORA-22926: specified trim length is greater than current LOB value's length
ORA-06512: at line 16
SQL>
SQL>
SQL> declare
  2    v_clob clob;
  3    v_xml xmltype;
  4    i pls_integer;
  5  begin
  6    v_clob := '<node>test</node>';
  7    i := 0;
  8    loop
  9      exit when i > 12;
10      v_clob := v_clob || v_clob;
11      i := i + 1;
12    end loop;
13    v_clob := '<root>' || v_clob || '</root>';
14    v_xml := xmltype(v_clob);
15
16    select XMLSERIALIZE(DOCUMENT V_XML AS CLOB)
17      into V_CLOB
18      from dual;
19
20    v_clob := trim(v_clob);
21  end;
22  /
PL/SQL procedure successfully completed.
SQL>
SQL>
SQL>Edited by: mdrake on Feb 23, 2011 9:32 AM