Binary large objects (BLOBs) example: GNOME Data Access 5 manual

## Binary large objects (BLOBs) example

The following example is available in the `samples/Blobs` source directory and illustrate how to manipulate BLOBs. This test program offers 2 operations which are to store the contents of a file to the database (which returns the ID of the stored data), and to fetch a stored data from the database from its ID (which creates a fetched_<ID> file).

The code is:

    #include <libgda/libgda.h>
    #include <libgda/sql-parser/gda-sql-parser.h>
    #include <libgda/gda-blob-op.h>

    GdaConnection *open_connection (void);
    static gboolean do_store (GdaConnection *cnc, const gchar *filename, GError **error);
    static gboolean do_fetch (GdaConnection *cnc, gint id, GError **error);

    int
    main (int argc, char *argv[])
    {
            GdaConnection *cnc;
    	const gchar *filename = NULL;
    	gint id = 0;
    	gboolean store;
    	GError *error = NULL;
    	gboolean result;

    	/* parse arguments */
    	if (argc != 3)
    		goto help;
    	if (! g_ascii_strcasecmp (argv[1], "store")) {
    		filename = argv[2];
    		store = TRUE;
    	}
    	else if (! g_ascii_strcasecmp (argv[1], "fetch")) {
    		id = atoi (argv[2]);
    		store = FALSE;
    	}
    	else
    		goto help;

    	/* do the job */
            gda_init ();
    	cnc = open_connection ();
    	if (store)
    		result = do_store (cnc, filename, &error);
    	else
    		result = do_fetch (cnc, id, &error);

    	if (gda_connection_get_transaction_status (cnc))
    		g_print ("Still in a transaction, all modifications will be lost when connection is closed\n");
            gda_connection_close (cnc);

    	if (!result) {
    		g_print ("ERROR: %s\n", error && error->message ? error->message : "No detail");
    		g_clear_error (&error);
    	}
    	else
    		g_print ("Ok.\n");

            return result ? 0 : 1;

     help:
    	g_print ("%s [store <filename> | fetch <ID>]\n", argv[0]);
    	return 0;
    }

    /*
     * Open a connection to the example.db file
     */
    GdaConnection *
    open_connection (void)
    {
            GdaConnection *cnc;
            GError *error = NULL;
            cnc = gda_connection_open_from_string ("SQLite", "DB_DIR=.;DB_NAME=testblob", NULL,
    					       GDA_CONNECTION_OPTIONS_NONE,
    					       &error);
            if (!cnc) {
                    g_print ("Could not open connection to SQLite database in testblob.db file: %s\n",
                             error && error->message ? error->message : "No detail");
                    exit (1);
            }
            return cnc;
    }

    static gboolean
    do_store (GdaConnection *cnc, const gchar *filename, GError **error)
    {
    	if (! g_file_test (filename, G_FILE_TEST_EXISTS) ||
    	    g_file_test (filename, G_FILE_TEST_IS_DIR)) {
    		g_set_error (error, 0, 0,
    			     "%s", "File does not exist or is a directory");
    		return FALSE;
    	}

    	GdaSqlParser *parser;
    	GdaStatement *stmt;
    	GdaSet *params, *newrow;
    	GdaHolder *holder;
    	GValue *value;
    	GdaBlob *blob;
    	gint res;

    	parser = gda_sql_parser_new ();
    	stmt = gda_sql_parser_parse_string (parser,
    					    "INSERT INTO blobstable (data) VALUES (##blob::blob)",
    					    NULL, error);
    	g_object_unref (parser);
    	if (!stmt)
    		return FALSE;

    	if (! gda_statement_get_parameters (stmt, &params, error)) {
    		g_object_unref (stmt);
    		return FALSE;
    	}

    	holder = gda_set_get_holder (params, "blob");
    	value = gda_value_new_blob_from_file (filename);
    	blob = (GdaBlob*) gda_value_get_blob (value);
    	g_assert (gda_holder_take_value (holder, value, NULL));

    	g_print ("Before writing BLOB: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	g_print ("STORING file '%s' to database BLOB\n", filename);
    	res = gda_connection_statement_execute_non_select (cnc, stmt, params, &newrow, error);
    	g_object_unref (params);
    	g_object_unref (stmt);

    	g_print ("After writing BLOB: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	if (newrow) {
    		GSList *list;
    		g_print ("Inserted row is (for each numbered column in the table):\n");
    		for (list = newrow->holders; list; list = list->next) {
    			const GValue *value;
    			gchar *tmp;
    			value = gda_holder_get_value (GDA_HOLDER (list->data));
    			tmp = gda_value_stringify (value);
    			g_print ("  [%s] = [%s]\n", gda_holder_get_id (GDA_HOLDER (list->data)), tmp);
    			g_free (tmp);
    		}
    		g_object_unref (newrow);
    	}
    	else
    		g_print ("Provider did not return the inserted row\n");

    	gda_connection_rollback_transaction (cnc, NULL, NULL);
    	g_print ("After rolling back blob READ transaction: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	return (res == -1) ? FALSE : TRUE;
    }

    static gboolean
    do_fetch (GdaConnection *cnc, gint id, GError **error)
    {
    	GdaSqlParser *parser;
    	GdaStatement *stmt;
    	GdaSet *params;
    	GdaDataModel *model;
    	const GValue *value;
    	GdaBlob *blob;
    	gboolean result = TRUE;

    	g_print ("Before reading BLOB: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	gchar *filename;
    	filename = g_strdup_printf ("fetched_%d", id);
    	g_print ("FETCHING BLOB with ID %d to file '%s'\n", id, filename);

    	parser = gda_sql_parser_new ();
    	stmt = gda_sql_parser_parse_string (parser,
    					    "SELECT data FROM blobstable WHERE id=##id::int",
    					    NULL, error);
    	g_object_unref (parser);
    	if (!stmt)
    		return FALSE;

    	if (! gda_statement_get_parameters (stmt, &params, error)) {
    		g_object_unref (stmt);
    		return FALSE;
    	}
    	g_assert (gda_set_set_holder_value (params, NULL, "id", id));
    	model = gda_connection_statement_execute_select (cnc, stmt, params, error);
    	g_object_unref (params);
    	g_object_unref (stmt);
    	if (! model)
    		return FALSE;

    	g_print ("After reading BLOB: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	value = gda_data_model_get_value_at (model, 0, 0, error);
    	if (!value) {
    		g_object_unref (model);
    		return FALSE;
    	}
    	g_assert (G_VALUE_TYPE (value) == GDA_TYPE_BLOB);

    	blob = (GdaBlob*) gda_value_get_blob (value);
    	if (blob->op) {
    		GValue *dest_value;
    		GdaBlob *dest_blob;

    		dest_value = gda_value_new_blob_from_file (filename);
    		dest_blob = (GdaBlob*) gda_value_get_blob (dest_value);
    		result = gda_blob_op_write_all (dest_blob->op, (GdaBlob*) blob);
    		gda_value_free (dest_value);
    	}
    	else
    		result = g_file_set_contents (filename, (gchar *) ((GdaBinary*)blob)->data,
    					     ((GdaBinary*)blob)->binary_length, error);
    	g_free (filename);
    	g_object_unref (model);

    	gda_connection_rollback_transaction (cnc, NULL, NULL);
    	g_print ("After rolling back blob READ transaction: %s\n", gda_connection_get_transaction_status (cnc) ?
    		 "Transaction started" : "No transaction started");

    	return result;
    }