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6<title>Berkeley DB Reference Guide: Transactional cursors</title>
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12<td><b><dl><dt>Berkeley DB Reference Guide:<dd>Berkeley DB Transactional Data Store Applications</dl></b></td>
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15<p align=center><b>Transactional cursors</b></p>
16<p>Berkeley DB cursors may be used inside a transaction, exactly as any other
17<a href="../../api_c/db_class.html">DB</a> method.  The enclosing transaction ID must be specified when
18the cursor is created, but it does not then need to be further specified
19on operations performed using the cursor.  One important point to
20remember is that a cursor <b>must be closed</b> before the enclosing
21transaction is committed or aborted.</p>
22<p>The following code fragment uses a cursor to store a new key in the cats
23database with four associated data items.  The key is a name.  The data
24items are a company name and a list of the breeds of cat owned.  Each
25of the data entries is stored as a duplicate data item.  In this
26example, transactions are necessary to ensure that either all or none
27of the data items appear in case of system or application failure.</p>
28<blockquote><pre>int
29main(int argc, char *argv)
30{
31	extern int optind;
32	DB *db_cats, *db_color, *db_fruit;
33	DB_ENV *dbenv;
34	int ch;
35<p>
36	while ((ch = getopt(argc, argv, "")) != EOF)
37		switch (ch) {
38		case '?':
39		default:
40			usage();
41		}
42	argc -= optind;
43	argv += optind;
44<p>
45	env_dir_create();
46	env_open(&dbenv);
47<p>
48	/* Open database: Key is fruit class; Data is specific type. */
49	db_open(dbenv, &db_fruit, "fruit", 0);
50<p>
51	/* Open database: Key is a color; Data is an integer. */
52	db_open(dbenv, &db_color, "color", 0);
53<p>
54	/*
55	 * Open database:
56	 *	Key is a name; Data is: company name, cat breeds.
57	 */
58	db_open(dbenv, &db_cats, "cats", 1);
59<p>
60	add_fruit(dbenv, db_fruit, "apple", "yellow delicious");
61<p>
62	add_color(dbenv, db_color, "blue", 0);
63	add_color(dbenv, db_color, "blue", 3);
64<p>
65<b>	add_cat(dbenv, db_cats,
66		"Amy Adams",
67		"Oracle",
68		"abyssinian",
69		"bengal",
70		"chartreaux",
71		NULL);</b>
72<p>
73	return (0);
74}
75<p>
76<b>int
77add_cat(DB_ENV *dbenv, DB *db, char *name, ...)
78{
79	va_list ap;
80	DBC *dbc;
81	DBT key, data;
82	DB_TXN *tid;
83	int fail, ret, t_ret;
84	char *s;
85<p>
86	/* Initialization. */
87	fail = 0;
88<p>
89	memset(&key, 0, sizeof(key));
90	memset(&data, 0, sizeof(data));
91	key.data = name;
92	key.size = strlen(name);
93<p>
94retry:	/* Begin the transaction. */
95	if ((ret = dbenv-&gt;txn_begin(dbenv, NULL, &tid, 0)) != 0) {
96		dbenv-&gt;err(dbenv, ret, "DB_ENV-&gt;txn_begin");
97		exit (1);
98	}
99<p>
100	/* Delete any previously existing item. */
101	switch (ret = db-&gt;del(db, tid, &key, 0)) {
102	case 0:
103	case DB_NOTFOUND:
104		break;
105	case DB_LOCK_DEADLOCK:
106	default:
107		/* Retry the operation. */
108		if ((t_ret = tid-&gt;abort(tid)) != 0) {
109			dbenv-&gt;err(dbenv, t_ret, "DB_TXN-&gt;abort");
110			exit (1);
111		}
112		if (fail++ == MAXIMUM_RETRY)
113			return (ret);
114		goto retry;
115	}
116<p>
117	/* Create a cursor. */
118	if ((ret = db-&gt;cursor(db, tid, &dbc, 0)) != 0) {
119		dbenv-&gt;err(dbenv, ret, "db-&gt;cursor");
120		exit (1);
121	}
122<p>
123	/* Append the items, in order. */
124	va_start(ap, name);
125	while ((s = va_arg(ap, char *)) != NULL) {
126		data.data = s;
127		data.size = strlen(s);
128		switch (ret = dbc-&gt;c_put(dbc, &key, &data, DB_KEYLAST)) {
129		case 0:
130			break;
131		case DB_LOCK_DEADLOCK:
132		default:
133			va_end(ap);
134<p>
135			/* Retry the operation. */
136			if ((t_ret = dbc-&gt;c_close(dbc)) != 0) {
137				dbenv-&gt;err(
138				    dbenv, t_ret, "dbc-&gt;c_close");
139				exit (1);
140			}
141			if ((t_ret = tid-&gt;abort(tid)) != 0) {
142				dbenv-&gt;err(dbenv, t_ret, "DB_TXN-&gt;abort");
143				exit (1);
144			}
145			if (fail++ == MAXIMUM_RETRY)
146				return (ret);
147			goto retry;
148		}
149	}
150	va_end(ap);
151<p>
152	/* Success: commit the change. */
153	if ((ret = dbc-&gt;c_close(dbc)) != 0) {
154		dbenv-&gt;err(dbenv, ret, "dbc-&gt;c_close");
155		exit (1);
156	}
157	if ((ret = tid-&gt;commit(tid, 0)) != 0) {
158		dbenv-&gt;err(dbenv, ret, "DB_TXN-&gt;commit");
159		exit (1);
160	}
161	return (0);
162}</b></pre></blockquote>
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