MySQL存儲二進制數據

晚上小研究了下MySQL存儲於讀取二進制數據的功能。關鍵步驟為以下三點:

1. 最重要的一點：存儲二進制數據的表的類型需要是blob類型（按長度不同分為tiny, media, long） 
2. 插入二進制數據時需要利用mysql_real_escape_string函數對數據進行轉換
3. 從數據庫中讀取二進制數據時需要利用mysql_fetch_length函數字段長度,該函數需要在mysql_fetch_row調用后才可以正常獲取結果

給出一個用C寫的一個存儲與讀取字段的小例子，寫的比較粗獷，見諒哈~

先來一個插入:

int
db_insert_object(void *object, unsigned int objsize)
{
    int ret;
    char *escape_object = NULL;
    char sql[1024];
    unsigned int escape_size = 2 * objsize + 2;
    int sql_len;
    MYSQL *mysql= NULL;

    /* connnect db */
    mysql = mysql_init(NULL);
    if( !mysql_real_connect(mysql, SERVER, USER, PASSWD, DATABASE, 0, NULL, 0) ){
        goto error1;
    }

    /* convert binary string */
    escape_object = (char *)malloc(escape_size);
    if( escape_object == NULL ){
        goto error1;
    }
    escape_size = mysql_real_escape_string(mysql, escape_object, (char *)object, objsize);

    sql_len = sprintf(sql, "insert into task(object) values('%s')", escape_object);
    ret = mysql_real_query(mysql, sql, sql_len);
    if( ret ){
        goto error1;
    }

    free(escape_object);
    mysql_close(mysql);
    return 0;

error1:
    printf("error: %s\n", mysql_error(mysql));
    if( mysql ) mysql_close(mysql);
    if( escape_object ) free(escape_object);
    return -1;
}

然后是讀取:

void *
db_fetch_object()
{
    MYSQL *mysql= NULL;
    MYSQL_RES *res = NULL;
    MYSQL_ROW row;
    unsigned long *row_len;
    char *object = NULL;
    const char *sql = "select object from task limit 1";
    unsigned long objsize;
    int ret;

    /* connnect db */
    mysql = mysql_init(NULL);
    if( !mysql_real_connect(mysql, SERVER, USER, PASSWD, DATABASE, 0, NULL, 0) ){
        goto error2;
    }

    /* get object */
    ret = mysql_real_query(mysql, sql, strlen(sql));
    if( ret ){
        goto error2;
    }

    res = mysql_store_result(mysql);
    if( res == NULL ){
        goto error2;
    }

    /* important */
    row = mysql_fetch_row(res);
    row_len = mysql_fetch_lengths(res);  /* get the object's length */
    if( row_len == NULL ){
        goto error2;
    }
    objsize = row_len[0];
    object  = (char*)malloc(objsize);
    if( object == NULL ){
        goto error2;
    }

    memcpy(object, row[0], objsize);

    mysql_close(mysql);
    mysql_free_result(res);
    return (void*)object;

error2:
    printf("error: %s\n", mysql_error(mysql));
    if( res ) mysql_free_result(res);
    if( mysql ) mysql_close(mysql);
    if( object ) free(object);
    return NULL;
}

PHP以及perl中的操作也是大同小異~

OVER~