PostgreSQL 7.4.11 Documentation
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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();

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