Qt/SQL - Get column type and name from table without record - c++

Question

Using Qt, I have to connect to a database and list column's types and names from a table. I have two constraints:
1 The database type must not be a problem (This has to work on PostgreSQL, SQL Server, MySQL, ...)
2 When I looked on the internet, I found solutions that work but only if there are one or more reocrd into the table. And I have to get column's type and name with or without record into this database.
I searched a lot on the internet but I didn't find any solutions.
I am looking for an answer in Qt/C++ or using a query that can do that.
Thanks for help !

Answer 1

QSqlDriver::record() takes a table name and returns a QSqlRecord, from which you can fetch the fields using QSqlRecord::field().
So, given a QSqlDatabase db,
fetch the driver with db.driver(),
fetch the list of tables with db.tables(),
fetch the a QSqlRecord for each table from driver->record(tableName), and
fetch the number of fields with record.count() and the name and type with record.field(x)

Answer 2

According to the previous answers, I make the implementation as below.It can work well, hope it can help you.
{
QSqlDatabase db = QSqlDatabase::addDatabase("QSLITE", "demo_conn"); //create a db connection
QString strDBPath = "db_path";
db.setDatabaseName(strDBPath); //set the db file
QSqlRecord record = db.record("table_name"); //get the record of the certain table
int n = record.count();
for(int i = 0; i < n; i++)
{
QString strField = record.fieldName(i);
}
}
QSqlDatabase::removeDatabase("demo_conn"); //remove the db connection

Answer 3

Getting column names and types is a database-specific operation. But you can have a single C++ function that will use the correct sql query according to the QSqlDriver you currently use:
QStringlist getColumnNames()
{
QString sql;
if (db.driverName.contains("QOCI", Qt::CaseInsensitive))
{
sql = ...
}
else if (db.driverName.contains("QPSQL", Qt::CaseInsensitive))
{
sql = ...
}
else
{
qCritical() << "unsupported db";
return QStringlist();
}
QSqlQuery res = db.exec(sql);
...
// getting names from db-specific sql query results
}

Answer 4

I don't know of any existing mechanism in Qt which allows that (though it might exist - maybe by using QSqlTableModel). If noone else knows of such a thing, I would just do the following:
Create data classes to store the information you require, e.g. a class TableInfo which stores a list of ColumnInfo objects which have a name and a type.
Create an interface e.g. ITableInfoReader which has a pure virtual TableInfo* retrieveTableInfo( const QString& tableName ) method.
Create one subclass of ITableInfoReader for every database you want to support. This allows doing queries which are only supported on one or a subset of all databases.
Create a TableInfoReaderFactory class which allows creation of the appropriate ITableInfoReader subclass dependent on the used database
This allows you to have your main code independent from the database, by using only the ITableInfoReader interface.
Example:
Input:
database: The QSqlDatabase which is used for executing queries
tableName: The name of the table to retrieve information about
ITableInfoReader* tableInfoReader =
_tableInfoReaderFactory.createTableReader( database );
QList< ColumnInfo* > columnInfos = tableInfoReader->retrieveTableInfo( tableName );
foreach( ColumnInfo* columnInfo, columnInfos )
{
qDebug() << columnInfo.name() << columnInfo.type();
}

Answer 5

I found the solution. You just have to call the record function from QSqlDatabase. You have an empty record but you can still read column types and names.