Table of Contents

• Obtaining a ResultSet from a stored function
  • From a Function Returning SETOF type
  • From a Function Returning a refcursor
• Calling stored procedure with transaction control

LightDB™ supports two types of stored objects, functions that can return a result value and - starting from v13 - procedures that can perform transaction control. Both types of stored objects are invoked using CallableStatement and the standard JDBC escape call syntax {call storedobject(?)}. The escapeSyntaxCallMode connection property controls how the driver transforms the call syntax to invoke functions or procedures.

The default mode, select, supports backwards compatibility for existing applications and supports function invocation only. This is required to invoke a void returning function. For new applications, use escapeSyntaxCallMode=callIfNoReturn to map CallableStatements with return values to stored functions and CallableStatements without return values to stored procedures.

Example 6.1. Calling a built in stored function

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

CallableStatement upperFunc = conn.prepareCall("{? = call upper( ? ) }");
upperFunc.registerOutParameter(1, Types.VARCHAR);
upperFunc.setString(2, "lowercase to uppercase");
upperFunc.execute();
String upperCased = upperFunc.getString(1);
upperFunc.close();

# Obtaining a ResultSet from a stored function

LightDB’s™ stored functions can return results in two different ways. The function may return either a refcursor value or a SETOF some datatype. Depending on which of these return methods are used determines how the function should be called.

## From a Function Returning SETOF type

Functions that return data as a set should not be called via the CallableStatement interface, but instead should use the normal Statement or PreparedStatement interfaces.

Example 6.2. Getting SETOF type values from a function

Statement stmt = conn.createStatement();
stmt.execute("CREATE OR REPLACE FUNCTION setoffunc() RETURNS SETOF int AS "
    + "' SELECT 1 UNION SELECT 2;' LANGUAGE sql");
ResultSet rs = stmt.executeQuery("SELECT * FROM setoffunc()");
while (rs.next())
{
    // do something
}
rs.close();
stmt.close();

## From a Function Returning a refcursor

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

Note

One notable limitation of the current support for a ResultSet created from a refcursor is that even though it is a cursor backed ResultSet, all data will be retrieved and cached on the client. The Statement fetch size parameter described in the section called “Getting results based on a cursor” is ignored. This limitation is a deficiency of the JDBC driver, not the server, and it is technically possible to remove it, we just haven’t found the time.

Example 6.3. Getting refcursor Value From a Function

// Setup function to call.
Statement stmt = conn.createStatement();
stmt.execute("CREATE OR REPLACE FUNCTION refcursorfunc() RETURNS refcursor AS '"
    + " DECLARE "
    + "    mycurs refcursor; "
    + " BEGIN "
    + "    OPEN mycurs FOR SELECT 1 UNION SELECT 2; "
    + "    RETURN mycurs; "
    + " END;' language plpgsql");
stmt.close();

// We must be inside a transaction for cursors to work.
conn.setAutoCommit(false);

// Function call.
CallableStatement func = conn.prepareCall("{? = call refcursorfunc() }");
func.registerOutParameter(1, Types.OTHER);
func.execute();
ResultSet results = (ResultSet) func.getObject(1);
while (results.next())
{
    // do something with the results.
}
results.close();
func.close();

It is also possible to treat the refcursor return value as a cursor name directly. To do this, use the getString of ResultSet. With the underlying cursor name, you are free to directly use cursor commands on it, such as FETCH and MOVE.

Example 6.4. Treating refcursor as a cursor name

conn.setAutoCommit(false);
CallableStatement func = conn.prepareCall("{? = call refcursorfunc() }");
func.registerOutParameter(1, Types.OTHER);
func.execute();
String cursorName = func.getString(1);
func.close();

**Example 6.5. Calling a stored procedure

This example shows how to call a LightDB™ procedure that uses transaction control.

// set up a connection
String url = "jdbc:lightdb://localhost/test";
Properties props = new Properties();
... other properties ...
// Ensure EscapeSyntaxCallmode property set to support procedures if no return value
props.setProperty("escapeSyntaxCallMode", "callIfNoReturn");
Connection con = DriverManager.getConnection(url, props);

// Setup procedure to call.
Statement stmt = con.createStatement();
stmt.execute("CREATE TEMP TABLE temp_val ( some_val bigint )");
stmt.execute("CREATE OR REPLACE PROCEDURE commitproc(a INOUT bigint) AS '"
    + " BEGIN "
    + "    INSERT INTO temp_val values(a); "
    + "    COMMIT; "
    + " END;' LANGUAGE plpgsql");
stmt.close();

// As of v13, we must be outside a transaction for procedures with transactions to work.
con.setAutoCommit(true);

// Procedure call with transaction
CallableStatement proc = con.prepareCall("{call commitproc( ? )}");
proc.setInt(1, 100);
proc.execute();
proc.close();