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9.6 KiB
217 lines
9.6 KiB
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<td align="right" valign="center"><img src="logo32.png" align="right" width="64" height="32" border="0"></td></tr></table><h1 align=center>QSqlField Class Reference<br><small>[<a href="sql.html">sql module</a>]</small></h1>
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<p>The QSqlField class manipulates the fields in SQL database tables
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and views.
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<a href="#details">More...</a>
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<p><tt>#include <<a href="qsqlfield-h.html">qsqlfield.h</a>></tt>
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<p><a href="qsqlfield-members.html">List of all member functions.</a>
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<h2>Public Members</h2>
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<ul>
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<li class=fn><a href="#QSqlField"><b>QSqlField</b></a> ( const QString & fieldName = QString::null, QVariant::Type type = QVariant::Invalid )</li>
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<li class=fn><a href="#QSqlField-2"><b>QSqlField</b></a> ( const QSqlField & other )</li>
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<li class=fn>QSqlField & <a href="#operator-eq"><b>operator=</b></a> ( const QSqlField & other )</li>
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<li class=fn>bool <a href="#operator-eq-eq"><b>operator==</b></a> ( const QSqlField & other ) const</li>
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<li class=fn>virtual <a href="#~QSqlField"><b>~QSqlField</b></a> ()</li>
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<li class=fn>virtual void <a href="#setValue"><b>setValue</b></a> ( const QVariant & value )</li>
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<li class=fn>virtual QVariant <a href="#value"><b>value</b></a> () const</li>
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<li class=fn>virtual void <a href="#setName"><b>setName</b></a> ( const QString & name )</li>
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<li class=fn>QString <a href="#name"><b>name</b></a> () const</li>
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<li class=fn>virtual void <a href="#setNull"><b>setNull</b></a> ()</li>
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<li class=fn>bool <a href="#isNull"><b>isNull</b></a> () const</li>
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<li class=fn>virtual void <a href="#setReadOnly"><b>setReadOnly</b></a> ( bool readOnly )</li>
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<li class=fn>bool <a href="#isReadOnly"><b>isReadOnly</b></a> () const</li>
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<li class=fn>void <a href="#clear"><b>clear</b></a> ( bool nullify = TRUE )</li>
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<li class=fn>QVariant::Type <a href="#type"><b>type</b></a> () const</li>
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</ul>
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<hr><a name="details"></a><h2>Detailed Description</h2>
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The QSqlField class manipulates the fields in SQL database tables
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and views.
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<p>
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<p> QSqlField represents the characteristics of a single column in a
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database table or view, such as the data type and column name. A
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field also contains the value of the database column, which can be
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viewed or changed.
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<p> Field data values are stored as QVariants. Using an incompatible
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type is not permitted. For example:
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<p> <pre>
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QSqlField f( "myfield", QVariant::Int );
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f.<a href="#setValue">setValue</a>( QPixmap() ); // will not work
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</pre>
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<p> However, the field will attempt to cast certain data types to the
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field data type where possible:
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<p> <pre>
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QSqlField f( "myfield", QVariant::Int );
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f.<a href="#setValue">setValue</a>( QString("123") ); // casts QString to int
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</pre>
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<p> QSqlField objects are rarely created explicitly in application
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code. They are usually accessed indirectly through <a href="qsqlrecord.html">QSqlRecord</a>
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or <a href="qsqlcursor.html">QSqlCursor</a> which already contain a list of fields. For
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example:
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<p> <pre>
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<a href="qsqlcursor.html">QSqlCursor</a> cur( "Employee" ); // create cursor using the 'Employee' table
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QSqlField* f = cur.<a href="qsqlrecord.html#field">field</a>( "name" ); // use the 'name' field
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f-><a href="#setValue">setValue</a>( "Dave" ); // set field value
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...
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</pre>
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<p> In practice we rarely need to extract a pointer to a field at all.
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The previous example would normally be written:
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<p> <pre>
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<a href="qsqlcursor.html">QSqlCursor</a> cur( "Employee" );
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cur.<a href="qsqlrecord.html#setValue">setValue</a>( "name", "Dave" );
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...
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</pre>
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<p>See also <a href="database.html">Database Classes</a>.
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<hr><h2>Member Function Documentation</h2>
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<h3 class=fn><a name="QSqlField"></a>QSqlField::QSqlField ( const <a href="qstring.html">QString</a> & fieldName = QString::null, <a href="qvariant.html#Type-enum">QVariant::Type</a> type = QVariant::Invalid )
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</h3>
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Constructs an empty field called <em>fieldName</em> of type <em>type</em>.
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<h3 class=fn><a name="QSqlField-2"></a>QSqlField::QSqlField ( const <a href="qsqlfield.html">QSqlField</a> & other )
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</h3>
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Constructs a copy of <em>other</em>.
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<h3 class=fn><a name="~QSqlField"></a>QSqlField::~QSqlField ()<tt> [virtual]</tt>
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</h3>
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Destroys the object and frees any allocated resources.
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<h3 class=fn>void <a name="clear"></a>QSqlField::clear ( bool nullify = TRUE )
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</h3>
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Clears the value of the field. If the field is read-only, nothing
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happens. If <em>nullify</em> is TRUE (the default), the field is set to
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NULL.
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<h3 class=fn>bool <a name="isNull"></a>QSqlField::isNull () const
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</h3>
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<p> Returns TRUE if the field is currently NULL; otherwise returns
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FALSE.
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<h3 class=fn>bool <a name="isReadOnly"></a>QSqlField::isReadOnly () const
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</h3>
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<p> Returns TRUE if the field's value is read only; otherwise returns
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FALSE.
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<h3 class=fn><a href="qstring.html">QString</a> <a name="name"></a>QSqlField::name () const
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</h3>
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<p> Returns the name of the field.
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<p>Example: <a href="sql.html#x2249">sql/overview/table4/main.cpp</a>.
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<h3 class=fn><a href="qsqlfield.html">QSqlField</a> & <a name="operator-eq"></a>QSqlField::operator= ( const <a href="qsqlfield.html">QSqlField</a> & other )
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</h3>
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Sets the field equal to <em>other</em>.
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<h3 class=fn>bool <a name="operator-eq-eq"></a>QSqlField::operator== ( const <a href="qsqlfield.html">QSqlField</a> & other ) const
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</h3>
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Returns TRUE if the field is equal to <em>other</em>; otherwise returns
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FALSE. Fields are considered equal when the following field
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properties are the same:
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<p> <ul>
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<li> <a href="#name">name</a>()
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<li> <a href="#isNull">isNull</a>()
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<li> <a href="#value">value</a>()
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<li> <a href="#isReadOnly">isReadOnly</a>()
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</ul>
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<p>
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<h3 class=fn>void <a name="setName"></a>QSqlField::setName ( const <a href="qstring.html">QString</a> & name )<tt> [virtual]</tt>
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</h3>
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<p> Sets the name of the field to <em>name</em>.
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<h3 class=fn>void <a name="setNull"></a>QSqlField::setNull ()<tt> [virtual]</tt>
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</h3>
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<p> Sets the field to NULL and clears the value using <a href="#clear">clear</a>(). If the
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field is read-only, nothing happens.
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<p> <p>See also <a href="#isReadOnly">isReadOnly</a>() and <a href="#clear">clear</a>().
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<h3 class=fn>void <a name="setReadOnly"></a>QSqlField::setReadOnly ( bool readOnly )<tt> [virtual]</tt>
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</h3>
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<p> Sets the read only flag of the field's value to <em>readOnly</em>.
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<p> <p>See also <a href="#setValue">setValue</a>().
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<h3 class=fn>void <a name="setValue"></a>QSqlField::setValue ( const <a href="qvariant.html">QVariant</a> & value )<tt> [virtual]</tt>
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</h3>
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Sets the value of the field to <em>value</em>. If the field is read-only
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(<a href="#isReadOnly">isReadOnly</a>() returns TRUE), nothing happens. If the data type of
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<em>value</em> differs from the field's current data type, an attempt is
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made to cast it to the proper type. This preserves the data type
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of the field in the case of assignment, e.g. a <a href="qstring.html">QString</a> to an
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integer data type. For example:
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<p> <pre>
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<a href="qsqlcursor.html">QSqlCursor</a> cur( "Employee" ); // 'Employee' table
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QSqlField* f = cur.<a href="qsqlrecord.html#field">field</a>( "student_count" ); // an integer field
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...
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f-><a href="#setValue">setValue</a>( myLineEdit->text() ); // cast the line edit text to an integer
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</pre>
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<p> <p>See also <a href="#isReadOnly">isReadOnly</a>().
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<h3 class=fn><a href="qvariant.html#Type-enum">QVariant::Type</a> <a name="type"></a>QSqlField::type () const
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</h3>
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<p> Returns the field's type as stored in the database.
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Note that the actual value might have a different type,
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Numerical values that are too large to store in a long
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int or double are usually stored as strings to prevent
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precision loss.
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<h3 class=fn><a href="qvariant.html">QVariant</a> <a name="value"></a>QSqlField::value () const<tt> [virtual]</tt>
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</h3>
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<p> Returns the value of the field as a <a href="qvariant.html">QVariant</a>.
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<p>Example: <a href="sql.html#x2250">sql/overview/table4/main.cpp</a>.
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<!-- eof -->
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<hr><p>
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This file is part of the <a href="index.html">Qt toolkit</a>.
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Copyright © 1995-2007
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<a href="http://www.trolltech.com/">Trolltech</a>. All Rights Reserved.<p><address><hr><div align=center>
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<table width=100% cellspacing=0 border=0><tr>
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<td>Copyright © 2007
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<a href="troll.html">Trolltech</a><td align=center><a href="trademarks.html">Trademarks</a>
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<td align=right><div align=right>Qt 3.3.8</div>
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