TField class

In unit DB

Provide access to the contents of a single field in a record.

Declaration

pascal

TField = class(TComponent)

Inheritance

Descends from it: TBinaryField TBlobField TBooleanField TDateTimeField TNumericField TObjectField TStringField TVariantField

Description

TField is an abstract class that defines access methods for a field in a record, controlled by a TDataset instance. It provides methods and properties to access the contents of the field in the current record. Reading one of the AsXXX properties of TField will access the field contents and return the contents as the desired type. Writing one of the AsXXX properties will write a value to the buffer represented by the TField instance.

TField is an abstract class, meaning that it should never be created directly. TDataset instances always create one of the descendent classes of TField, depending on the type of the underlying data.

Properties

`AsBCD`	public	Access the field's contents as a BCD (Binary coded Decimal).
`AsBoolean`	public	Access the field's contents as a Boolean value.
`AsBytes`	public	Retrieve the contents of the field as an array of bytes.
`AsCurrency`	public	Access the field's contents as a Currency value.
`AsDateTime`	public	Access the field's contents as a TDateTime value.
`AsExtended`	public
`AsFloat`	public	Access the field's contents as a floating-point (Double) value.
`AsLongint`	public	Access the field's contents as a 32-bit signed integer (longint) value.
`AsLongWord`	public	Access field contents as 32-bit unsigned integer (longword/cardinal).
`AsLargeInt`	public	Access the field's contents as a 64-bit signed integer (longint) value.
`AsInteger`	public	Access the field's contents as a 32-bit signed integer (longint) value.
`AsSingle`	public
`AsString`	public	Access the field's contents as an AnsiString value.
`AsAnsiString`	public	Return field contents as an ANSI string.
`AsUnicodeString`	public	Field contents as a UnicodeString.
`AsUTF8String`	public	Field contents as a UTF8 String.
`AsWideString`	public	Access the field's contents as a WideString value.
`AsVariant`	public	Access the field's contents as a Variant value.
`AttributeSet`	public	Not used: dictionary information.
`Calculated`	public	Is the field a calculated field ?
`CanModify`	public	Can the field's contents be modified.
`CurValue`	public	Current value of the field.
`DataSet`	public	Dataset this field belongs to.
`DataSize`	public	Size of the field's data.
`DataType`	public	The data type of the field.
`DisplayName`	public	User-readable fieldname.
`DisplayText`	public	Formatted field value.
`EditMask`	public	Specify an edit mask for an edit control.
`EditMaskPtr`	public	Alias for EditMask.
`FieldNo`	public	Number of the field in the record.
`IsIndexField`	public	Is the field an indexed field ?
`IsNull`	public	Is the field empty.
`NewValue`	public	The new value of the field.
`Offset`	public	Offset of the field's value in the dataset buffer.
`Size`	public	Logical size of the field.
`Text`	public	Text representation of the field.
`ValidChars`	public	Characters that are valid input for the field's content.
`Value`	public	Value of the field as a variant value.
`OldValue`	public	Old value of the field.
`LookupList`	public	List of lookup values.
`FieldDef`	public	Fielddef associated with this field.
`Alignment`	published	Alignment for this field.
`CustomConstraint`	published	Custom constraint for the field's value.
`ConstraintErrorMessage`	published	Message to display if the CustomConstraint constraint is violated.
`DefaultExpression`	published	Default value for the field.
`DisplayLabel`	published	Name of the field for display purposes.
`DisplayWidth`	published	Width of the field in characters.
`FieldKind`	published	The kind of field.
`FieldName`	published	Name of the field.
`HasConstraints`	published	Does the field have any constraints defined.
`Index`	published	Index of the field in the list of fields.
`ImportedConstraint`	published	Constraint for the field value on the level of the underlying database.
`KeyFields`	published	Key fields to use when looking up a field value.
`LookupCache`	published	Should lookup values be cached.
`LookupDataSet`	published	Dataset with lookup values.
`LookupKeyFields`	published	Names of fields on which to perform a locate.
`LookupResultField`	published	Name of field to use as lookup value.
`Lookup`	published	Is the field a lookup field.
`Origin`	published	Original fieldname of the field.
`ParentField`	published
`ProviderFlags`	published	Flags for provider or update support.
`ReadOnly`	published	Is the field read-only.
`Required`	published	Does the field require a value.
`Visible`	published	Should the field be shown in grids.

Methods

`AccessError`	protected
`CheckInactive`	protected
`CheckTypeSize`	protected
`Change`	protected
`Bind`	protected
`DataChanged`	protected
`FreeBuffers`	protected
`GetAsBCD`	protected
`GetAsBoolean`	protected
`GetAsBytes`	protected
`GetAsCurrency`	protected
`GetAsDateTime`	protected
`GetAsExtended`	protected
`GetAsFloat`	protected
`GetAsLargeInt`	protected
`GetAsLongint`	protected
`GetAsLongWord`	protected
`GetAsInteger`	protected
`GetAsVariant`	protected
`GetOldValue`	protected
`GetAsSingle`	protected
`GetAsString`	protected
`GetAsAnsiString`	protected
`GetAsUnicodeString`	protected
`GetAsUTF8String`	protected
`GetAsWideString`	protected
`GetCanModify`	protected
`GetClassDesc`	protected
`GetDataSize`	protected
`GetDefaultWidth`	protected
`GetDisplayName`	protected
`GetCurValue`	protected
`GetNewValue`	protected
`GetIsNull`	protected
`GetParentComponent`	protected	Returns the parent component.
`GetText`	protected
`HasParent`	protected	Does the component have a parent ?
`Notification`	protected	Called by components that are freed and which received a FreeNotification.
`PropertyChanged`	protected
`ReadState`	protected	Read the component's state from a stream.
`SetAsBCD`	protected
`SetAsBoolean`	protected
`SetAsBytes`	protected
`SetAsCurrency`	protected
`SetAsDateTime`	protected
`SetAsExtended`	protected
`SetAsFloat`	protected
`SetAsLargeInt`	protected
`SetAsLongint`	protected
`SetAsLongWord`	protected
`SetAsInteger`	protected
`SetAsVariant`	protected
`SetAsSingle`	protected
`SetAsString`	protected
`SetAsAnsiString`	protected
`SetAsUnicodeString`	protected
`SetAsUTF8String`	protected
`SetAsWideString`	protected
`SetDataset`	protected
`SetDataType`	protected
`SetNewValue`	protected
`SetSize`	protected
`SetParentComponent`	protected	Set the parent component.
`SetParentField`	protected
`SetText`	protected
`SetVarValue`	protected
`Create`	public	Create a new TField instance.
`Destroy`	public	Destroy the TField instance.
`Assign`	public	Copy properties from one TField instance to another.
`AssignValue`	public	Assign value of a variant record to the field.
`Clear`	public	Clear the field contents.
`FocusControl`	public	Set focus to the first control connected to this field.
`GetData`	public	Get the data from this field.
`IsBlob`	public	Is the field a BLOB field (untyped data of indeterminate size).
`IsValidChar`	public	Check whether a character is valid input for the field.
`RefreshLookupList`	public	Refresh the lookup list.
`SetData`	public	Save the field data.
`SetFieldType`	public	Set the field data type.
`Validate`	public	Validate the data buffer.

Events

`OnChange`	published	Event triggered when the field's value has changed.
`OnGetText`	published	Event to format the field's content.
`OnSetText`	published	Event to set the field's content based on a user-formatted string.
`OnValidate`	published	Event to validate the value of a field before it is written to the data buffer.

Inherited

From TComponent (69)

_AddRef _Release BeforeDestruction CanObserve ChangeName ComObject ComponentCount ComponentIndex Components ComponentState ComponentStyle DefineProperties DesignInfo DestroyComponents Destroying ExecuteAction FindComponent FreeNotification FreeOnRelease GetChildOwner GetChildParent GetChildren GetDeltaStreams GetEnumerator GetIDsOfNames GetNamePath GetObservers GetOwner GetTypeInfo GetTypeInfoCount iicrGetComponent InsertComponent Invoke IsImplementorOf Loaded Loading Name ObserverAdded Observers OnGetDeltaStreams Owner PaletteCreated QueryInterface ReadDeltaState ReadDeltaStream ReferenceInterface RemoveComponent RemoveFreeNotification RemoveFreeNotifications SafeCallException SetAncestor SetChildOrder SetDesigning SetDesignInstance SetInline SetName SetSubComponent Tag ToString TToStringNameMode UpdateAction Updated UpdateRegistry Updating ValidateContainer ValidateInsert ValidateRename VCLComObject WriteState

From TPersistent (4)

AssignTo FPOAttachObserver FPODetachObserver FPONotifyObservers

From TObject (37)

AfterConstruction CheckDisposed ClassInfo ClassName ClassNameIs ClassParent ClassType CleanupInstance DefaultHandler DefaultHandlerStr Dispatch DispatchStr Disposed DisposeOf Equals FieldAddress Free FreeInstance GetDisposed GetHashCode GetInterface GetInterfaceByStr GetInterfaceEntry GetInterfaceEntryByStr GetInterfaceTable GetInterfaceWeak GetLastCastErrorInfo InheritsFrom InitInstance InstanceSize MethodAddress MethodName newinstance QualifiedClassName StringMessageTable SystemHasExtendedRTTI UnitName

An experiment, built from development snapshots. Not the official Free Pascal or Lazarus documentation.