Qt QSqlQuery bindValue works with ? but not with :placeholders

问题

I'm working with SQLite, doing insert into table. Folowwing

QSqlQuery testQuery(QString("INSERT INTO test(testcol) VALUES(?)"));
testQuery.bindValue(0, someQStringObg);
testQuery.exec();

works, but

QSqlQuery testQuery(QString("INSERT INTO test(testcol) VALUES(:val)"));
testQuery.bindValue(":val", someQStringObg);
testQuery.exec();

don't. testQuery.lastError().text() returns No query Unable to fetch row

Have no clue why things are that way, but really want to find out.

回答1:

Please use prepare as the official example:

QSqlQuery testQuery;
testQuery.prepare("INSERT INTO test(testcol) VALUES(:val)");
testQuery.bindValue(":val", someQStringObj);
testQuery.exec();

The reason for the error is that the query was executed before binding to the corresponding placeholder. You can see the relevant part of the constructor documentation:

If query is not an empty string, it will be executed.

来源：https://stackoverflow.com/questions/20786003/qt-qsqlquery-bindvalue-works-with-but-not-with-placeholders