[QT] Chapter 10: Database

Chapter ten ： database

1. The main ：
   Create connection ： Will create a QSqIDatabase class Example , Only a call open() Function before the connection can be used .
   QSqlQuery class An interface is provided , Used to perform SQL Statement and browse the result set of the query . To execute a SQL sentence , You simply create one QSqlQuery object , And then call QSqlQuery : : ex-ec() Function , for example :

QSqlQuery query;
query.exec( "select * from student");

2. QTSQL modular ：
   Can pass QSqIDatabase::drivers() Method to get the current sql Which databases are supported in the module .
3. When creating multiple connections , Connection name should be specified , Can't default

QSqlDatabase  db1 = QSqIDatabase::addDatabase("QSQLITE",connect1);
QSqlDatabase db2 = QSqlDatabase::addDatabase("QSQLITE",connect2);

Query result set ：
seek(int n) : query Point to the second part of the result set n Bar record . Specify the current location
first() : query The first record pointing to the result set .
last() : query Points to the last record in the result set .
next() : query Point to the next record , Every time the function is executed , It points to the next adjacent record .previous(): Point to previous record , Every time the function is executed , It points to the next record .record(): Get the record you are pointing to .
value(int n): Get the value of the property . among n Represents the second page of your query n Attributes
query.at():l obtain query The number of the record in the result set query.record().indexOf(“name”):ll return "name" The column number of
query.record().count():l Get the attributes in each record （ Namely column ） The number of
Record.field(n):ll Get the current record's n A field

4. The core ：
   increase Delete check Change