Question

My sqlite3 database contains strings of text containing special characters (e.g. macrons such as Ā, Ō). Since sqlite3 does not directly ship with unicode handling, I would like to use Qt's localeAwareComparison as a means to enable locale-aware collation. Results of queries using ORDER BY text should be ordered lexicographically A < Ā < B, instead of A < B < Ā.

I was able to implement a working prototype using the following comparison method:

int sqliteLocaleAwareCompare(void *, int ll, const void * l, int rl, const void * r) {
    QString left = QString::fromUtf16((const ushort *)l, ll/2);
    QString right = QString::fromUtf16((const ushort *)r, rl/2);
    return QString::localeAwareCompare(left, right);
}

The collation is then added to sqlite3 (which is compiled along with my code using the official amalgamation):

// Open the database
QSqlDatabase db = QSqlDatabase::addDatabase("QSQLITE");
db.setDatabaseName(database_path);
if (!db.open()) {
    qDebug() << "ERROR: Database could not be opened.";
}

// Retrieve the database handle
QVariant handle = db.driver()->handle();
sqlite3* sqlite_db = *static_cast<sqlite3**>(handle.data());

// Initialize sqlite3's global variables
sqlite3_initialize();

// Add the collation
sqlite3_create_collation(sqlite_db, "LOCALE", SQLITE_UTF16, nullptr, sqliteLocaleAwareCompare);

My question is twofold:

Is this the correct way to extend sqlite3's functionality using Qt5?
Why does this snippet result in the correct behavior if compiled and run on my desktop computer (Mac OS X), but not if compiled and run on Android (emulator & actual device)?

Thank you in advance for your help!

Behavior on Mac OS X

Results:
Ābc
Alpha
Beta
Gamma
Ōdachi

localeAwareComparison-Output:
comparing: "Ōdachi" with "Ābc" result 1
comparing: "Beta" with "Gamma" result -1
comparing: "Gamma" with "Ōdachi" result -1
comparing: "Gamma" with "Ābc" result 1
comparing: "Beta" with "Ābc" result 1
comparing: "Alpha" with "Ōdachi" result -1
comparing: "Alpha" with "Gamma" result -1
comparing: "Alpha" with "Beta" result -1
comparing: "Alpha" with "Ābc" result 1
Inserting role name:  "tt"

Locale:
QLocale(English, Latin, UnitedStates)
"UTF-8"

Behavior on Android

Results:
Alpha
Beta
Gamma
Ābc
Ōdachi

localeAwareComparison-Output:
comparing: "Ōdachi" with "Ābc" result 1
comparing: "Beta" with "Gamma" result -5
comparing: "Gamma" with "Ōdachi" result -126
comparing: "Gamma" with "Ābc" result -125
comparing: "Alpha" with "Ōdachi" result -132
comparing: "Alpha" with "Ābc" result -131
comparing: "Alpha" with "Gamma" result -6
comparing: "Alpha" with "Beta" result -1
Inserting role name:  "tt"

Locale:
QLocale(English, Latin, UnitedStates)
"UTF-8"

The last two lines are the results of the following commands (if this helps):

QLocale locale;
qDebug() << locale;

QTextCodec * codec = QTextCodec::codecForLocale();
qDebug() << codec->name();

Locale-aware collation in SQLite using Qt

0 个答案: