Added sample of changing returned by engine metadata and using changed metadata in Statement::execute()

examples/interfaces/13.null_pk.cpp

@@ -0,0 +1,153 @@
+/*
+ *	PROGRAM:	Object oriented API samples.
+ *	MODULE:		13.null_pk.cpp
+ *	DESCRIPTION:	Changing metadata, passed from DB engine, and using modified
+ *					copy later. Useful for changing nullability or coercing datatype.
+ *
+ *					Example for the following interfaces:
+ *					IMessageMetadata - describe input and output data format
+ *					IMetadataBuilder - tool to modify/create metadata
+ *
+ * The contents of this file are subject to the Interbase Public
+ * License Version 1.0 (the "License"); you may not use this file
+ * except in compliance with the License. You may obtain a copy
+ * of the License at http://www.Inprise.com/IPL.html
+ *
+ * Software distributed under the License is distributed on an
+ * "AS IS" basis, WITHOUT WARRANTY OF ANY KIND, either express
+ * or implied. See the License for the specific language governing
+ * rights and limitations under the License.
+ *
+ * The Original Code was created by Inprise Corporation
+ * and its predecessors. Portions created by Inprise Corporation are
+ * Copyright (C) Inprise Corporation.
+ *
+ * All Rights Reserved.
+ * Contributor(s): ______________________________________.
+ *					Alex Peshkov, 2013, 2020
+ */
+
+#include "ifaceExamples.h"
+
+static IMaster* master = fb_get_master_interface();
+
+int main()
+{
+	int rc = 0;
+
+	// set default password if none specified in environment
+	setenv("ISC_USER", "sysdba", 0);
+	setenv("ISC_PASSWORD", "masterkey", 0);
+
+	// status vector and main dispatcher
+	ThrowStatusWrapper status(master->getStatus());
+	IProvider* prov = master->getDispatcher();
+
+	// declare pointers to required interfaces
+	IAttachment* att = NULL;
+	ITransaction* tra = NULL;
+
+	// Interface executes prepared SQL statement
+	IStatement* stmt = NULL;
+
+	// Interfaces provides access to format of data in messages
+	IMessageMetadata* meta = NULL;
+
+	// Interface makes it possible to change format of data or define it yourself
+	IMetadataBuilder* builder = NULL;
+
+	const char* sqlStr =
+	    "Insert into COUNTRY values(?, ?)";
+
+	try
+	{
+		// attach employee db
+		att = prov->attachDatabase(&status, "employee", 0, NULL);
+
+		// start transaction
+		tra = att->startTransaction(&status, 0, NULL);
+
+		// prepare statement
+		stmt = att->prepare(&status, tra, 0, sqlStr, SAMPLES_DIALECT, 0);
+
+		// build metadata
+		meta = stmt->getInputMetadata(&status);
+		builder = meta->getBuilder(&status);
+
+		// set nullability on fields
+		for (unsigned n = 0; n < meta->getCount(&status); ++n)
+		{
+			unsigned t = meta->getType(&status, n);
+			builder->setType(&status, n, t | 1);
+		}
+
+		// IMetadata should be ready
+		meta->release();
+		meta = NULL;
+		meta = builder->getMetadata(&status);
+
+		// no need in builder any more
+		builder->release();
+		builder = NULL;
+
+		// allocate buffer on stack
+		char buffer[256];
+		unsigned len = meta->getMessageLength(&status);
+		if (len > sizeof(buffer))
+		{
+			throw "Input message length too big - can't continue";
+		}
+
+		// all null
+		for (unsigned n = 0; n < meta->getCount(&status); ++n)
+		{
+ 			short* flag = (short*)&buffer[meta->getNullOffset(&status, n)];
+	 		*flag = -1;
+	 		// setting value for NULL field makes no sense - skip it
+	 	}
+
+		// this should throw - passing NULLs to not-NULL columns
+		// can work only with something like before insert trigger
+	    stmt->execute(&status, tra, meta, buffer, NULL, NULL);
+
+		// close interfaces
+		stmt->free(&status);
+		stmt = NULL;
+
+		meta->release();
+		meta = NULL;
+
+		tra->rollback(&status);
+		tra = NULL;
+
+		att->detach(&status);
+		att = NULL;
+	}
+	catch (const FbException& error)
+	{
+		// handle error
+		rc = 1;
+
+		char buf[256];
+		master->getUtilInterface()->formatStatus(buf, sizeof(buf), error.getStatus());
+		fprintf(stderr, "%s\n", buf);
+	}
+
+	// release interfaces after error caught
+	if (builder)
+		builder->release();
+	if (meta)
+		meta->release();
+	if (stmt)
+		stmt->release();
+	if (tra)
+		tra->release();
+	if (att)
+		att->release();
+
+	prov->release();
+	status.dispose();
+
+	return rc;
+}
+