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31.5. Calling Stored Functions

PostgreSQL's JDBC driver fully supports calling PostgreSQL stored functions.

Example 31-4. Calling a built in stored function

This example shows how to call a PostgreSQL built in function, upper, which simply converts the supplied string argument to uppercase.

// Turn transactions off.
con.setAutoCommit(false);
// Procedure call.
CallableStatement upperProc = con.prepareCall("{ ? = call upper( ? ) }");
upperProc.registerOutParameter(1, Types.VARCHAR);
upperProc.setString(2, "lowercase to uppercase");
upperProc.execute();
String upperCased = upperProc.getString(1);
upperProc.close();

31.5.1. Using the CallableStatement Interface

All the considerations that apply for Statement and PreparedStatement apply for CallableStatement but in addition you must also consider one extra restriction:

  • You can only call a stored function from within a transaction.

31.5.2. Obtaining ResultSet from a stored function

PostgreSQL's stored function can return results by means of a refcursor value. A refcursor.

As an extension to JDBC, the PostgreSQL JDBC driver can return refcursor values as ResultSet values.

Example 31-5. Getting refcursor values from a function

When calling a function that returns a refcursor you must cast the return type of getObject to a ResultSet

// Turn transactions off.
con.setAutoCommit(false);
// Procedure call.
CallableStatement proc = con.prepareCall("{ ? = call doquery ( ? ) }");
proc.registerOutParameter(1, Types.Other);
proc.setInt(2, -1);
proc.execute();
ResultSet results = (ResultSet) proc.getObject(1);
while (results.next()) {
  // do something with the results...
}
results.close();
proc.close();

It is also possible to treat the refcursor return value as a distinct type in itself. The JDBC driver provides the org.postgresql.PGRefCursorResultSet class for this purpose.

Example 31-6. Treating refcursor as a distinct type

con.setAutoCommit(false);
CallableStatement proc = con.prepareCall("{ ? = call doquery ( ? ) }");
proc.registerOutParameter(1, Types.Other);
proc.setInt(2, 0);
org.postgresql.PGRefCursorResultSet refcurs 
    = (PGRefCursorResultSet) con.getObject(1);
String cursorName = refcurs.getRefCursor();
proc.close();

Comments


June 8, 2005, 12:02 a.m.

Pay close attention to the syntax here. The "call" keyword MUST be lowercase, or you will get an error. The spacing doesn't appear to be vital.


June 8, 2005, 12:09 a.m.

This JDBC functionality does not allow for "void" types for your stored functions. It will return an exception of "unsupported return type".

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