Detailed Description
The QSqlField class manipulates the fields in SQL database tables
and views.
QSqlField represents the characteristics of a single column in a
database table or view, such as the data type and column name. A
field also contains the value of the database column, which can be
viewed or changed.
Field data values are stored as QVariants. Using an incompatible
type is not permitted. For example:
QSqlField f( "myfield", QVariant::Int );
f.setValue( QPixmap() ); // will not work
However, the field will attempt to cast certain data types to the
field data type where possible:
QSqlField f( "myfield", QVariant::Int );
f.setValue( QString("123") ); // casts QString to int
QSqlField objects are rarely created explicitly in application
code. They are usually accessed indirectly through QSqlRecord
or QSqlCursor which already contain a list of fields. For
example:
QSqlCursor cur( "Employee" ); // create cursor using the 'Employee' table
QSqlField* f = cur.field( "name" ); // use the 'name' field
f->setValue( "Dave" ); // set field value
...
In practice we rarely need to extract a pointer to a field at all.
The previous example would normally be written:
QSqlCursor cur( "Employee" );
cur.setValue( "name", "Dave" );
...
See also Database Classes.
Member Function Documentation
QSqlField::QSqlField ( const QString & fieldName = QString::null, QVariant::Type type = QVariant::Invalid )
Constructs an empty field called fieldName of type type.
QSqlField::QSqlField ( const QSqlField & other )
Constructs a copy of other.
QSqlField::~QSqlField () [virtual]
Destroys the object and frees any allocated resources.
void QSqlField::clear ( bool nullify = TRUE )
Clears the value of the field. If the field is read-only, nothing
happens. If nullify is TRUE (the default), the field is set to
NULL.
bool QSqlField::isNull () const
Returns TRUE if the field is currently NULL; otherwise returns
FALSE.
bool QSqlField::isReadOnly () const
Returns TRUE if the field's value is read only; otherwise returns
FALSE.
QString QSqlField::name () const
Returns the name of the field.
Example: sql/overview/table4/main.cpp.
QSqlField & QSqlField::operator= ( const QSqlField & other )
Sets the field equal to other.
bool QSqlField::operator== ( const QSqlField & other ) const
Returns TRUE if the field is equal to other; otherwise returns
FALSE. Fields are considered equal when the following field
properties are the same:
void QSqlField::setName ( const QString & name ) [virtual]
Sets the name of the field to name.
void QSqlField::setNull () [virtual]
Sets the field to NULL and clears the value using clear(). If the
field is read-only, nothing happens.
See also isReadOnly() and clear().
void QSqlField::setReadOnly ( bool readOnly ) [virtual]
Sets the read only flag of the field's value to readOnly.
See also setValue().
void QSqlField::setValue ( const QVariant & value ) [virtual]
Sets the value of the field to value. If the field is read-only
(isReadOnly() returns TRUE), nothing happens. If the data type of
value differs from the field's current data type, an attempt is
made to cast it to the proper type. This preserves the data type
of the field in the case of assignment, e.g. a QString to an
integer data type. For example:
QSqlCursor cur( "Employee" ); // 'Employee' table
QSqlField* f = cur.field( "student_count" ); // an integer field
...
f->setValue( myLineEdit->text() ); // cast the line edit text to an integer
See also isReadOnly().
Returns the field's type as stored in the database.
Note that the actual value might have a different type,
Numerical values that are too large to store in a long
int or double are usually stored as strings to prevent
precision loss.
QVariant QSqlField::value () const [virtual]
Returns the value of the field as a QVariant.
Example: sql/overview/table4/main.cpp.
This file is part of the Qt toolkit.
Copyright © 1995-2005
Trolltech. All Rights Reserved.
