QSqlField Class

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# QSqlField Class Reference
[sql module]

The QSqlField class manipulates the fields in SQL database tables and views. More...

`#include <qsqlfield.h>`

List of all member functions.

## Public Members

- QSqlField ( const QString & fieldName = QString::null, QVariant::Type type = QVariant::Invalid )
- QSqlField ( const QSqlField & other )
- QSqlField & operator= ( const QSqlField & other )
- bool operator== ( const QSqlField & other ) const
- virtual ~QSqlField ()
- virtual void setValue ( const QVariant & value )
- virtual QVariant value () const
- virtual void setName ( const QString & name )
- QString name () const
- virtual void setNull ()
- bool isNull () const
- virtual void setReadOnly ( bool readOnly )
- bool isReadOnly () const
- void clear ( bool nullify = TRUE )
- QVariant::Type type () const

## 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:

- name()
- isNull()
- value()
- isReadOnly()

### 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().

### QVariant::Type QSqlField::type () const

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.

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