24 XSU for PL/SQL

Generating XML with DBMS_XMLQuery()

Generating XML results in a CLOB that contains the XML document. To use DBMS_XMLQuery and the XSU generation engine, follow these steps:

1. Create a context handle by calling the DBMS_XMLQuery.getCtx function and supplying it the query, either as a CLOB or a VARCHAR2.

2. Bind possible values to the query using the DBMS_XMLQuery.bind function. The binds work by binding a name to the position. For example, the query can be select * from employees where employee_id = :EMPNO_VAR. Here you are binding the value for the EMPNO_VAR using the setBindValue function.

3. Set optional arguments like the ROW tag name, the ROWSET tag name, or the number of rows to fetch, and so on.

4. Fetch the XML as a CLOB using the getXML() functions. getXML() can be called to generate the XML with or without a DTD or schema.

5. Close the context.

Here are some examples that use the DBMS_XMLQuery PL/SQL package.

XSU Generating XML Example 1: Generating XML from Simple Queries (PL/SQL)

In this example, you select rows from table employees, and obtain an XML document as a CLOB. First get the context handle by passing in a query and then call the getXMLClob routine to get the CLOB value. The document is in the same encoding as the database character set.

declare
  queryCtx DBMS_XMLquery.ctxType;
  result CLOB;
begin

  -- set up the query context...!
  queryCtx := DBMS_XMLQuery.newContext('select * from employees');
 
  -- get the result..!
  result := DBMS_XMLQuery.getXML(queryCtx);
  -- Now you can use the result to put it in tables/send as messages..
  printClobOut(result);
  DBMS_XMLQuery.closeContext(queryCtx);  -- you must close the query handle..
end;

XSU Generating XML Example 2: Printing CLOB to Output Buffer

printClobOut() is a simple function that prints the CLOB to the output buffer. If you run this PL/SQL code in SQL*Plus, the result of the CLOB is printed to the screen. Set the serveroutput to on in order to see the results. You may have to increase your display buffer to see all the output:

set serveroutput on size 200000
set long 20000

Here is the code:

CCREATE OR REPLACE PROCEDURE printClobOut(result IN OUT NOCOPY CLOB) is
xmlstr varchar2(32767);
line varchar2(2000);
begin
  xmlstr := dbms_lob.SUBSTR(result,32767);
  loop
    exit when xmlstr is null;
    line := substr(xmlstr,1,instr(xmlstr,chr(10))-1);
    dbms_output.put_line('| '||line);
    xmlstr := substr(xmlstr,instr(xmlstr,chr(10))+1);
  end loop;
end;

XSU Generating XML Example 3: Changing ROW and ROWSET Tag Names

With the XSU PL/SQL API you can also change the ROW and the ROWSET tag names. These are the default names placed around each row of the result, and round the whole document, respectively. The procedures, setRowTagName and setRowSetTagName accomplish this as shown in the following example:

--Setting the ROW tag names

declare
   queryCtx DBMS_XMLQuery.ctxType;
   result CLOB;
begin
   -- set the query context.
   queryCtx := DBMS_XMLQuery.newContext('select * from employees');
 
   DBMS_XMLQuery.setRowTag(queryCtx,'EMP');       -- sets the row tag name
   DBMS_XMLQuery.setRowSetTag(queryCtx,'EMPSET'); -- sets rowset tag name

   result := DBMS_XMLQuery.getXML(queryCtx);      -- get the result

   printClobOut(result);  -- print the result..!
   DBMS_XMLQuery.closeContext(queryCtx);          -- close the query handle;
end;

The resulting XML document has an EMPSET document element. Each row is separated using the EMP tag.

XSU Generating XML Example 4: Using setMaxRows() and setSkipRows()

The results from the query generation can be paginated by using:

• setMaxRows function. This sets the maximum number of rows to be converted to XML. This is relative to the current row position from which the last result was generated.

• setSkipRows function. This specifies the number of rows to skip before converting the row values to XML.

For example, to skip the first 3 rows of the employees table and then print out the rest of the rows 10 at a time, you can set the skipRows to 3 for the first batch of 10 rows and then set skipRows to 0 for the rest of the batches.

As in the case of XML SQL Utility's Java API, call the keepObjectOpen() function to ensure that the state is maintained between fetches. The default behavior is to close the state after a fetch. For multiple fetches, you must determine when there are no more rows to fetch. This can be done by setting the setRaiseNoRowsException(). This causes an exception to be raised if no rows are written to the CLOB. This can be caught and used as the termination condition.

-- Pagination of results

--Setting the ROW tag names

declare
   queryCtx DBMS_XMLQuery.ctxType;
   result CLOB;
begin
   -- set the query context.
   queryCtx := DBMS_XMLQuery.newContext('select * from employees');
 
   DBMS_XMLQuery.setRowTag(queryCtx,'EMP'); -- sets the row tag name
   DBMS_XMLQuery.setRowSetTag(queryCtx,'EMPSET'); -- sets rowset tag name

   result := DBMS_XMLQuery.getXML(queryCtx); -- get the result

   printClobOut(result);  -- print the result..!
   DBMS_XMLQuery.closeContext(queryCtx);  -- close the query handle;
end;

XSU Generating XML Example 5: Binding Values to the SQL Statement

The following example illustrates the use of bind variables in the SQL statement:

declare
  queryCtx DBMS_XMLquery.ctxType;
  result CLOB;
begin

queryCtx := DBMS_XMLQuery.newContext('select * from employees where employee_id
         = :EMPLOYEE_ID and first_name = :FIRST_NAME');

--No longer needed:
--DBMS_XMLQuery.clearBindValues(queryCtx);
DBMS_XMLQuery.setBindValue(queryCtx,'EMPLOYEE_ID',100);
DBMS_XMLQuery.setBindValue(queryCtx,'FIRST_NAME','Steven');

result := DBMS_XMLQuery.getXML(queryCtx);

--printClobOut(result); 

DBMS_XMLQuery.setBindValue(queryCtx,'FIRST_NAME','Neena');

result := DBMS_XMLQuery.getXML(queryCtx);

--printClobOut(result);
end;

create or replace procedure insProc(xmlDoc IN CLOB, tableName IN VARCHAR2) is
   insCtx DBMS_XMLSave.ctxType;
   rows number;
 begin
    insCtx := DBMS_XMLSave.newContext(tableName);  -- get the context handle
    rows := DBMS_XMLSave.insertXML(insCtx,xmlDoc); -- this inserts the document
    DBMS_XMLSave.closeContext(insCtx);             -- this closes the handle
end;

XSU Inserting XML Example 6: Inserting Values into All Columns (PL/SQL)

This example creates a procedure, insProc, which takes in:

• An XML document as a CLOB

• A table name to put the document into

and then inserts the XML document into the table:

create or replace procedure insProc(xmlDoc IN CLOB, tableName IN VARCHAR2) is
   insCtx DBMS_XMLSave.ctxType;
   rows number;
 begin
    insCtx := DBMS_XMLSave.newContext(tableName); -- get the context handle
    rows := DBMS_XMLSave.insertXML(insCtx,xmlDoc); -- this inserts the document
    DBMS_XMLSave.closeContext(insCtx);            -- this closes the handle
end;

This procedure can now be called with any XML document and a table name. For example, a call of the form:

execute insProc(xmlDocument, 'hr.employees');

generates an INSERT statement of the form:

INSERT INTO hr.employees (employee_id, last_name, job_id, manager_id, hire_date,
       salary, department_id VALUES(?,?,?,?,?,?,?);

and the element tags in the input XML document matching the column names will be matched and their values bound. For the code snippet shown earlier, if you send it the following XML document:

<?xml version='1.0'?>
<ROWSET>
  <ROW num="1">
    <EMPLOYEE_ID>7369</EMPLOYEE_ID>
    <LAST_NAME>Smith</LAST_NAME>
    <JOB_ID>CLERK</JOB_ID>
    <MANAGER_ID>7902</MANAGER_ID>
    <HIRE_DATE>12/17/1980 0:0:0</HIRE_DATE>
    <SALARY>800</SALARY>_
    <DEPARTMENT_ID>20</DEPARTMENT_ID>
  </ROW>
  <!-- additional rows ... -->
</ROWSET>

you would have a new row in the employees table containing the values 7369, Smith, CLERK, 7902, 12/17/1980, 800, 20 for the columns named. Any element absent inside the row element would is considered a null value.

XSU Inserting XML Example 7: Inserting Values into Certain Columns (PL/SQL)

In certain cases, you may not want to insert values into all columns. This might be true when the values that you are getting is not the complete set and you need triggers or default values to be used for the rest of the columns. The code that appears later shows how this can be done.

Assume that you are getting the values only for the employee number, name, and job, and that the salary, manager, department number and hiredate fields are filled in automatically. You create a list of column names that you want the insert to work on and then pass it to the DBMS_XMLSave procedure. The setting of these values can be done by calling setUpdateColumnName() procedure repeatedly, passing in a column name to update every time. The column name settings can be cleared using clearUpdateColumnNames().

create or replace procedure testInsert( xmlDoc IN clob) is
  insCtx DBMS_XMLSave.ctxType;
  doc clob;
  rows number;
begin
 
   insCtx := DBMS_XMLSave.newContext('hr.employees'); -- get the save context..!

   DBMS_XMLSave.clearUpdateColumnList(insCtx); -- clear the update settings

   -- set the columns to be updated as a list of values..
   DBMS_XMLSave.setUpdateColumn(insCtx,'EMPLOYEE_ID'); 
   DBMS_XMLSave.setUpdateColumn(insCtx,'LAST_NAME');
   DBMS_XMLSave.setUpdatecolumn(insCtx,'JOB_ID');

   -- Now insert the doc. This will only insert into EMPLOYEE_ID, LAST_NAME, and
   --   JOB_ID columns
   rows := DBMS_XMLSave.insertXML(insCtx, xmlDoc); 
   DBMS_XMLSave.closeContext(insCtx);

end;
/

If you call the procedure passing in a CLOB as a document, an INSERT statement of the form:

INSERT INTO hr.employees (employee_id, last_name, job_id) VALUES (?, ?, ?);

is generated. Note that in the earlier example, if the inserted document contains values for the other columns (HIRE_DATE, and so on), those are ignored.

An insert is performed for each ROW element that is present in the input. These inserts are batched by default.

XSU Updating XML Example 8: Updating XML Document Key Columns (PL/SQL)

Consider the PL/SQL procedure:

create or replace procedure testUpdate ( xmlDoc IN clob) is
  updCtx DBMS_XMLSave.ctxType; 
  rows number;
begin
   
   updCtx := DBMS_XMLSave.newContext('hr.employees');  -- get the context
   DBMS_XMLSave.clearUpdateColumnList(updCtx);   -- clear the update settings..
  
   DBMS_XMLSave.setKeyColumn(updCtx,'EMPLOYEE_ID'); -- set EMPLOYEE_ID as key column
   rows := DBMS_XMLSave.updateXML(updCtx,xmlDoc);  -- update the table.
   DBMS_XMLSave.closeContext(updCtx);              -- close the context..!

end;
/

In this example, when the procedure is executed with a CLOB value that contains the document described earlier, two UPDATE statements would be generated. For the first ROW element, you would generate an UPDATE statement to update the fields as shown next:

UPDATE hr.employees SET salary = 1800 AND department_id = 30 WHERE employee_id = 7369;

and for the second ROW element,

UPDATE hr.employees SET salary = 2000 AND hire_date = 12/31/1992 WHERE employee_id = 2290;

XSU Updating XML Example 9: Specifying a List of Columns to Update (PL/SQL)

You may want to specify the list of columns to update. This would speed up the processing since the same UPDATE statement can be used for all the ROW elements. Also you can ignore other tags which occur in the document. Note that when you specify a list of columns to update, an element corresponding to one of the update columns, if absent, will be treated as NULL.

If you know that all the elements to be updated are the same for all the ROW elements in the XML document, then you can use the setUpdateColumnName() procedure to set the column name to update.

create or replace procedure testUpdate(xmlDoc IN CLOB) is
  updCtx DBMS_XMLSave.ctxType;
  rows number;
begin
  
   updCtx := DBMS_XMLSave.newContext('hr.employees');
   DBMS_XMLSave.setKeyColumn(updCtx,'EMPLOYEE_ID'); -- set EMPLOYEE_ID as key column

   -- set list of columnst to update.
   DBMS_XMLSave.setUpdateColumn(updCtx,'SALARY');
   DBMS_XMLSave.setUpdateColumn(updCtx,'JOB_ID');

   rows := DBMS_XMLSave.updateXML(updCtx,xmlDoc); -- update the XML document..!
   DBMS_XMLSave.closeContext(updCtx);   -- close the handle

end;

XSU Deleting XML Example 10: Deleting Operations for Each Row (PL/SQL)

Consider the delete example shown here:

create or replace procedure testDelete(xmlDoc IN clob) is
  delCtx DBMS_XMLSave.ctxType;
  rows number;
begin

   delCtx  := DBMS_XMLSave.newContext('hr.employees');
   DBMS_XMLSave.setKeyColumn(delCtx,'EMPLOYEE_ID');

   rows := DBMS_XMLSave.deleteXML(delCtx,xmlDoc);
   DBMS_XMLSave.closeContext(delCtx);
end;

If you use the same XML document shown for the update example, you would end up with two DELETE statements,

DELETE FROM hr.employees WHERE employee_id=7369 AND salary=1800 AND department_id=30; 
DELETE FROM hr.employees WHERE employee_id=2200 AND salary=2000 AND hire_date=12/31/1992;

The DELETE statements were formed based on the tag names present in each ROW element in the XML document.

XSU Example 11: Deleting by Specifying the Key Values (PL/SQL)

If instead you want the delete to only use the key values as predicates, you can use the setKeyColumn function to set this.

create or replace package testDML AS
   saveCtx DBMS_XMLSave.ctxType := null;   -- a single static variable

   procedure insertXML(xmlDoc in clob);
   procedure updateXML(xmlDoc in clob);
   procedure deleteXML(xmlDoc in clob);

 end;

create or replace package body testDML AS
  
  rows number;
  
  procedure insertXML(xmlDoc in clob) is
  begin
    rows := DBMS_XMLSave.insertXML(saveCtx,xmlDoc);
  end;
   
  procedure updateXML(xmlDoc in clob) is
  begin
    rows := DBMS_XMLSave.updateXML(saveCtx,xmlDoc);
  end;
  
  procedure deleteXML(xmlDoc in clob) is
  begin
    rows := DBMS_XMLSave.deleteXML(saveCtx,xmlDoc);
  end;

begin
  saveCtx := DBMS_XMLSave.newContext('hr.employees'); -- create the context once
  DBMS_XMLSave.setKeyColumn(saveCtx, 'EMPLOYEE_ID');  -- set the key column name.
end;

Here a single DELETE statement of the form,

DELETE FROM hr.employees WHERE employee_id=?

will be generated and used for all ROW elements in the document.

XSU Deleting XML Example 12: Reusing the Context Handle (PL/SQL)

In all the three cases described earlier (insert, update, and delete) the same context handle can be used to do more than one operation. That is, you can perform more than one insert using the same context provided all of those inserts are going to the same table that was specified when creating the save context. The context can also be used to mix updates, deletes, and inserts.

For example, the following code shows how one can use the same context and settings to insert, delete, or update values depending on the user's input.

The example uses a PL/SQL supplied package static variable to store the context so that the same context can be used for all the function calls.

create or replace package testDML AS
   saveCtx DBMS_XMLSave.ctxType := null;   -- a single static variable

   procedure insert(xmlDoc in clob);
   procedure update(xmlDoc in clob);
   procedure delete(xmlDoc in clob);

 end;
/

create or replace package body testDML AS
  
  procedure insert(xmlDoc in clob) is
  row number;
  begin
    row := DBMS_XMLSave.insertXML(saveCtx, xmlDoc);
  end;
  
  procedure update(xmlDoc in clob) is
  begin
    row := DBMS_XMLSave.updateXML(saveCtx, xmlDoc);
  end;
  
  procedure delete(xmlDoc in clob) is
  begin
    row := DBMS_XMLSave.deleteXML(saveCtx, xmlDoc);
  end;

  begin
    saveCtx := DBMS_XMLSave.newContext('hr.employees'); -- create the context 
once..!
    DBMS_XMLSave.setKeyColumn(saveCtx, 'EMPLOYEE_ID');   -- set the key column name.
  end;
end;
/

In the earlier package, you create a context once for the whole package (thus the session) and then reuse the same context for performing inserts, updates and deletes.

Users of this package can now call any of the three routines to update the employees table:

testDML.insert(xmlclob);
testDML.delete(xmlclob);
testDML.update(xmlclob);

All of these calls would use the same context. This would improve the performance of these operations, particularly if these operations are performed frequently.

XSU Exception Handling in PL/SQL

Here is an XSU PL/SQL exception handling example:

declare
  queryCtx DBMS_XMLQuery.ctxType;
  result clob;
  errorNum NUMBER;
  errorMsg VARCHAR2(200);
begin

  queryCtx := DBMS_XMLQuery.newContext('select * from employees where df = dfdf');

  -- set the raise exception to true..
  DBMS_XMLQuery.setRaiseException(queryCtx, true);
  DBMS_XMLQuery.setRaiseNoRowsException(queryCtx, true);

  -- set propagate original exception to true to get the original exception..!
  DBMS_XMLQuery.propagateOriginalException(queryCtx,true);
  result := DBMS_XMLQuery.getXML(queryCtx);

  exception
    when others then
      -- get the original exception
      DBMS_XMLQuery.getExceptionContent(queryCtx,errorNum, errorMsg);
      dbms_output.put_line(' Exception caught ' || TO_CHAR(errorNum)
                   || errorMsg );
end; 
/