我使用BLOB將對象插入到SQLite數據庫。插入後,我可以用「SELECT」語句獲取數據,數據是正確的,但當用「SQLite數據庫瀏覽器」瀏覽數據庫時,「TASK_HEAD」行是「空」。 但是,如果我銷燬剛剛插入的對象,我不能再獲取正確的數據,並且指針「pHead」指向其「id」成員的內容是「的地址」鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿鉿UG?」當在VS2008中以調試模式讀取時。已成功將blob數據插入SQLite數據庫,但無法獲取插入的數據
下面是一個例子:
// user-defined data type
typedef std::string TASK_ID;
struct TASK_HEAD
{
TASK_ID id;
std::string userData;
int Size()
{
return (id.size() + userData.size()) * sizeof(TCHAR);
}
};
// when TEST_INSIDE is defined, pHead is invalid; but if undef it, I can get the "head" I just inserted
// and if the blob data is a string (when USING_STRING is defined), I can get the string inserted into the db even though the "test" string has been destroyed
void CDBWriter::WriteTestData()
{
// open db
sqlite3* db = NULL;
int nRet = sqlite3_open(DATABASE_NAME.c_str(), &db);
if (nRet != SQLITE_OK)
{
return;
}
if (db != NULL)
{
// create a table
std::string cmdCreate("CREATE TABLE IF NOT EXISTS testTable (id TEXT NOT NULL, TASK_HEAD BLOB, PRIMARY KEY(id));");
char* errMsg = NULL;
nRet = sqlite3_exec(db , cmdCreate.c_str() , 0 , 0 , &errMsg);
if(errMsg != NULL)
{
sqlite3_free(errMsg);
errMsg = NULL;
return;
}
//#define USING_STRING
#define TEST_INSIDE
#ifndef TEST_INSIDE
TASK_HEAD head;
#endif // TEST_INSIDE
// insert blob data
const TASK_ID newID(NewGUID()); // NewGUID returns string like this: "5811307F-7AA7-4C44-831F-774FC5832627"
string query = "INSERT OR REPLACE INTO testTable (id, TASK_HEAD) VALUES ('";
query += newID;
query += "', ?1);";
sqlite3_stmt* res = NULL;
nRet = sqlite3_prepare_v2(db, query.c_str(), query.length(), &res, 0);
{
#ifdef TEST_INSIDE
TASK_HEAD head;
#endif // TEST_INSIDE
head.id = newID;
#ifdef USING_STRING
std::string test("ewsjoafijdoaijeofsafsd");
nRet = sqlite3_bind_blob (res, 1, test.c_str(), test.size(), SQLITE_TRANSIENT);
#else
int nsizeHead = sizeof(head);
int nSizeHeadSt = sizeof(TASK_HEAD);
int sizeString = sizeof(std::string);
size_t nLen = newID.size();
//nRet = sqlite3_bind_blob (res, 1, &head, sizeof(head), SQLITE_TRANSIENT);
nRet = sqlite3_bind_blob (res, 1, &head, head.Size(), SQLITE_TRANSIENT);
#endif // USING_STRING
if (SQLITE_OK == nRet)
{
nRet = sqlite3_step(res);
}
if (nRet != SQLITE_OK && nRet != SQLITE_DONE)
{
return;
}
}
// get all columns in the database
query = "SELECT * FROM testTable;";
nRet = sqlite3_prepare_v2 (db, query.c_str(), query.length(), &res, 0);
if (SQLITE_OK == nRet)
{
while (SQLITE_ROW == sqlite3_step(res))
{
#ifdef USING_STRING
const char* pHead = (const char*)sqlite3_column_blob(res, 1);
#else
const TASK_HEAD *pHead = (const TASK_HEAD*)sqlite3_column_blob(res, 1);
#endif // USING_STRING
continue;
}
}
sqlite3_finalize(res);
sqlite3_close(db);
}
}
起初,我想這可能是傳遞給sqlite3_bind_blob字節的問題,所以我獲得對象的字節有一個愚蠢的方法,你可以在這裏看到(TASK_HEAD的size()函數),但這沒有幫助。 然後我嘗試使用SQLITE_STATIC而不是SQLITE_TRANSIENT,仍然無法工作。 有什麼問題?我知道這是一個不好的解決方案,將對象插入數據庫,我只是想知道爲什麼我不能讀回我的數據插入數據庫。
非常感謝!這有很大幫助。順便說一句,有沒有關於BLOB數據的更多介紹(爲什麼它不能用指針和動態緩衝區構建)? – YoungLearner
你可以看看http://en.wikipedia.org/wiki/Serialization –
謝謝,這有幫助。 – YoungLearner