您所在位置：主题：数据操作和游标
张贝注册
[专家分：0] 发布于 2012-07-11 09:04:00
数据操作和游标
1. 设置自定义比较函数。
static int my_int_compare(ham_db_t *db, ham_u8_t *lhs, ham_size_t lhs_size, ham_u8_t *rhs, ham_size_t rhs_size) {
int nlhs=*(int *)lhs;
int nrhs=*(int *)rhs;
if (nlhs<nrhs) return -1;
if (nrhs>nlhs) return +1;
return 0;
}
int main(int argc, char **argv)
{
ham_status_t st;
ham_db_t *db;
if ((st=ham_new(&db))!=HAM_SUCCESS) {
printf("ham_new failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
if ((st=ham_set_compare_func(db, my_int_compare))!=HAM_SUCCESS) {
printf("ham_set_compare_func failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
if ((st=ham_create_ex(db, "test.db", 0, 0664))!=HAM_SUCCESS) {
printf("ham_create_ex failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
// ...
}
2. ham_insert，插入数据。 当flags参数设置为HAM_DUPLICATE时，如果该key已经存在，则插入重复键。flags为HAM_OVERWRITE时，如果该key已经存在则覆盖它。flags如果没有被指定，当key重复时，insert操作将报错。注意，insert之前需要将key和value这两个结构体先初始化为0.
void example_of_insert() {
ham_key_t key;
ham_record_t record;
memset(&key, 0, sizeof(key));
memset(&record, 0, sizeof(record));
.
key.data="color";
key.size=strlen(key.data)+1; /* +1 for the terminating zero-byte */
record.data="green";
record.size=strlen(record.data)+1; /* +1 for the terminating zero-byte */
.
if ((st=ham_insert(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
printf("ham_insert failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
}
3. ham_find，查找数据。基于指定的key查找。
void example_of_find() {
ham_status_t st;
ham_key_t key;
ham_record_t record;
memset(&key, 0, sizeof(key));
memset(&record, 0, sizeof(record));
key.data="color";
key.size=strlen(key.data)+1; /* +1 for the terminating zero-byte */
.
if ((st=ham_find(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
printf("ham_find failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
}
注意：这里的record.data的内存空间是由hamsterdb内部分配，因此只要在调用任何hamsterdb的任何函数，该数据可能会被覆盖，如果打算自行分配内存，如下:
memset(&record, 0, sizeof(record));
record.flags=HAM_RECORD_USER_ALLOC;
record.data=malloc(6);
.
if ((st=ham_find(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
// ...
}
这里内存分配是否可以容纳所有record数据，需要自行判断。
4. hamsterdb可以读取和替换已存在record的partial data。
5. hamsterdb针对ham_find or ham_cursor_find两个函数都提供了近似查找的flag，如ham_find(db, NULL, &key, &record, HAM_FIND_NEAR_MATCH)。
* HAM_FIND_EXACT_MATCH: This is the default setting. If exactly this key exists then the record of this key will be returned.
* HAM_FIND_LT_MATCH ‘find’ flag ‘Less Than’: retrieves the last record with a key which is less than the specified key.
* HAM_FIND_GT_MATCH ‘find’ flag ‘Greater Than’: retrieves the first record with a key which is greater than the specified key.
* HAM_FIND_LEQ_MATCH ‘find’ flag ‘Less or EQual’: retrieves the last record with a key which is less or equal than the specified key.
* HAM_FIND_GEQ_MATCH ‘find’ flag ‘Greater or Equal’: retrieves the first record with a key which is greater or equal than the specified key.
* HAM_FIND_NEAR_MATCH ‘find’ flag ‘Any Near Or Equal’: retrieves the record which’ key matches the specified key and when such a key is not available hamsterdb will retrieve either the last record which’ key is less than the specified key or the first record which’ key is larger than the specified key, whichever of these records is located first.
6. 游标操作相关的函数：
1) ham_status_t ham_cursor_create(ham_db_t *db, ham_txn_t *txn, ham_u32_t flags, ham_cursor_t **cursor);
2) ham_status_t ham_cursor_move(ham_cursor_t *cursor, ham_key_t *key, ham_record_t *record, ham_u32_t flags);
3) ham_status_t ham_cursor_insert(ham_cursor_t *cursor, ham_key_t *key, ham_record_t *record, ham_u32_t flags);
4) ham_status_t ham_cursor_find(ham_cursor_t *cursor, ham_key_t *key, ham_u32_t flags);
5) ham_status_t ham_cursor_overwrite(ham_cursor_t *cursor, ham_record_t *record, ham_u32_t flags);
6) ham_status_t ham_cursor_erase(ham_cursor_t *cursor, ham_u32_t flags);
7) ham_status_t ham_cursor_clone(ham_cursor_t *src, ham_cursor_t **dest);
8) ham_status_t ham_cursor_close(ham_cursor_t *cursor);
7. hamsterdb关闭：
1) ham_status_t ham_close(ham_db_t *db, ham_u32_t flags); 该函数只是关闭数据库，可以重新打开。
2) ham_status_t ham_delete(ham_db_t *db); 该函数将删除ham_new创建的数据库句柄，以防止内存泄露。
本文有北大青鸟整理[url]http://www.yingxiaoshipeixun.com[/url]
1. 设置自定义比较函数。
static int my_int_compare(ham_db_t *db, ham_u8_t *lhs, ham_size_t lhs_size, ham_u8_t *rhs, ham_size_t rhs_size) {
int nlhs=*(int *)lhs;
int nrhs=*(int *)rhs;
if (nlhs<nrhs) return -1;
if (nrhs>nlhs) return +1;
return 0;
}
int main(int argc, char **argv)
{
ham_status_t st;
ham_db_t *db;
if ((st=ham_new(&db))!=HAM_SUCCESS) {
printf("ham_new failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
if ((st=ham_set_compare_func(db, my_int_compare))!=HAM_SUCCESS) {
printf("ham_set_compare_func failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
if ((st=ham_create_ex(db, "test.db", 0, 0664))!=HAM_SUCCESS) {
printf("ham_create_ex failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
// ...
}
2. ham_insert，插入数据。 当flags参数设置为HAM_DUPLICATE时，如果该key已经存在，则插入重复键。flags为HAM_OVERWRITE时，如果该key已经存在则覆盖它。flags如果没有被指定，当key重复时，insert操作将报错。注意，insert之前需要将key和value这两个结构体先初始化为0.
void example_of_insert() {
ham_key_t key;
ham_record_t record;
memset(&key, 0, sizeof(key));
memset(&record, 0, sizeof(record));
.
key.data="color";
key.size=strlen(key.data)+1; /* +1 for the terminating zero-byte */
record.data="green";
record.size=strlen(record.data)+1; /* +1 for the terminating zero-byte */
.
if ((st=ham_insert(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
printf("ham_insert failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
}
3. ham_find，查找数据。基于指定的key查找。
void example_of_find() {
ham_status_t st;
ham_key_t key;
ham_record_t record;
memset(&key, 0, sizeof(key));
memset(&record, 0, sizeof(record));
key.data="color";
key.size=strlen(key.data)+1; /* +1 for the terminating zero-byte */
.
if ((st=ham_find(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
printf("ham_find failed: %d (%s)\n", st, ham_strerror(st));
exit(-1);
}
}
注意：这里的record.data的内存空间是由hamsterdb内部分配，因此只要在调用任何hamsterdb的任何函数，该数据可能会被覆盖，如果打算自行分配内存，如下:
memset(&record, 0, sizeof(record));
record.flags=HAM_RECORD_USER_ALLOC;
record.data=malloc(6);
.
if ((st=ham_find(db, NULL, &key, &record, 0))!=HAM_SUCCESS) {
// ...
}
这里内存分配是否可以容纳所有record数据，需要自行判断。
4. hamsterdb可以读取和替换已存在record的partial data。
5. hamsterdb针对ham_find or ham_cursor_find两个函数都提供了近似查找的flag，如ham_find(db, NULL, &key, &record, HAM_FIND_NEAR_MATCH)。
* HAM_FIND_EXACT_MATCH: This is the default setting. If exactly this key exists then the record of this key will be returned.
* HAM_FIND_LT_MATCH ‘find’ flag ‘Less Than’: retrieves the last record with a key which is less than the specified key.
* HAM_FIND_GT_MATCH ‘find’ flag ‘Greater Than’: retrieves the first record with a key which is greater than the specified key.
* HAM_FIND_LEQ_MATCH ‘find’ flag ‘Less or EQual’: retrieves the last record with a key which is less or equal than the specified key.
* HAM_FIND_GEQ_MATCH ‘find’ flag ‘Greater or Equal’: retrieves the first record with a key which is greater or equal than the specified key.
* HAM_FIND_NEAR_MATCH ‘find’ flag ‘Any Near Or Equal’: retrieves the record which’ key matches the specified key and when such a key is not available hamsterdb will retrieve either the last record which’ key is less than the specified key or the first record which’ key is larger than the specified key, whichever of these records is located first.
6. 游标操作相关的函数：
1) ham_status_t ham_cursor_create(ham_db_t *db, ham_txn_t *txn, ham_u32_t flags, ham_cursor_t **cursor);
2) ham_status_t ham_cursor_move(ham_cursor_t *cursor, ham_key_t *key, ham_record_t *record, ham_u32_t flags);
3) ham_status_t ham_cursor_insert(ham_cursor_t *cursor, ham_key_t *key, ham_record_t *record, ham_u32_t flags);
4) ham_status_t ham_cursor_find(ham_cursor_t *cursor, ham_key_t *key, ham_u32_t flags);
5) ham_status_t ham_cursor_overwrite(ham_cursor_t *cursor, ham_record_t *record, ham_u32_t flags);
6) ham_status_t ham_cursor_erase(ham_cursor_t *cursor, ham_u32_t flags);
7) ham_status_t ham_cursor_clone(ham_cursor_t *src, ham_cursor_t **dest);
8) ham_status_t ham_cursor_close(ham_cursor_t *cursor);
7. hamsterdb关闭：
1) ham_status_t ham_close(ham_db_t *db, ham_u32_t flags); 该函数只是关闭数据库，可以重新打开。
2) ham_status_t ham_delete(ham_db_t *db); 该函数将删除ham_new创建的数据库句柄，以防止内存泄露。
本文有北大青鸟整理[url]http://www.yingxiaoshipeixun.com[/url]