TField¶

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

Declaration¶

Source position: db.pas line 288

type

  TField = class(TComponent)
  public
    constructor Create;
    destructor Destroy;
    procedure Assign;
    procedure AssignValue;
    procedure Clear;
    procedure FocusControl;
    function GetData(Buffer: Pointer) : Boolean; overload;
    function GetData(Buffer: Pointer; NativeFormat: Boolean) : Boolean; overload;
    class function IsBlob : Boolean;
    function IsValidChar : Boolean;
    procedure RefreshLookupList;
    procedure SetData(Buffer: Pointer); overload;
    procedure SetData(Buffer: Pointer; NativeFormat: Boolean); overload;
    procedure SetFieldType;
    procedure Validate;
    property AsBCD: TBCD; {rw}
    property AsBoolean: Boolean; {rw}
    property AsBytes: TBytes; {rw}
    property AsCurrency: Currency; {rw}
    property AsDateTime: TDateTime; {rw}
    property AsExtended: Extended; {rw}
    property AsFloat: Double; {rw}
    property AsLongint: LongInt; {rw}
    property AsLongWord: LongWord; {rw}
    property AsLargeInt: LargeInt; {rw}
    property AsInteger: LongInt; {rw}
    property AsSingle: Single; {rw}
    property AsString: string; {rw}
    property AsAnsiString: AnsiString; {rw}
    property AsUnicodeString: UnicodeString; {rw}
    property AsUTF8String: UTF8String; {rw}
    property AsWideString: WideString; {rw}
    property AsVariant: variant; {rw}
    property AttributeSet: string; {rw}
    property Calculated: Boolean; {rw}
    property CanModify: Boolean; {r}
    property CurValue: Variant; {r}
    property DataSet: TDataSet; {rw}
    property DataSize: Integer; {r}
    property DataType: TFieldType; {r}
    property DisplayName: string; {r}
    property DisplayText: string; {r}
    property EditMask: TEditMask; {rw}
    property EditMaskPtr: TEditMask; {r}
    property FieldNo: LongInt; {r}
    property IsIndexField: Boolean; {r}
    property IsNull: Boolean; {r}
    property NewValue: Variant; {rw}
    property Offset: Word; {r}
    property Size: Integer; {rw}
    property Text: string; {rw}
    property ValidChars: TFieldChars; {rw}
    property Value: variant; {rw}
    property OldValue: variant; {r}
    property LookupList: TLookupList; {r}
    property FieldDef: TFieldDef; {r}
  published
    property Alignment: TAlignment; {rwd}
    property CustomConstraint: string; {rw}
    property ConstraintErrorMessage: string; {rw}
    property DefaultExpression: string; {rw}
    property DisplayLabel: string; {rws}
    property DisplayWidth: LongInt; {rws}
    property FieldKind: TFieldKind; {rw}
    property FieldName: string; {rw}
    property HasConstraints: Boolean; {r}
    property Index: LongInt; {rw}
    property ImportedConstraint: string; {rw}
    property KeyFields: string; {rw}
    property LookupCache: Boolean; {rwd}
    property LookupDataSet: TDataSet; {rw}
    property LookupKeyFields: string; {rw}
    property LookupResultField: string; {rw}
    property Lookup: Boolean; {rws}
    property Origin: string; {rw}
    property ParentField: TObjectField; {rw}
    property ProviderFlags: TProviderFlags; {rw}
    property ReadOnly: Boolean; {rwd}
    property Required: Boolean; {rwd}
    property Visible: Boolean; {rwd}
    property OnChange: TFieldNotifyEvent; {rw}
    property OnGetText: TFieldGetTextEvent; {rw}
    property OnSetText: TFieldSetTextEvent; {rw}
    property OnValidate: TFieldNotifyEvent; {rw}
  end;

Inheritance¶

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¶

Member	Visibility	Description
Alignment	published	Alignment for this field.
AsAnsiString	public	Return field contents as an ANSI string.
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.
AsInteger	public	Access the field's contents as a 32-bit signed integer (longint) value.
AsLargeInt	public	Access the field's contents as a 64-bit signed integer (longint) 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).
AsSingle	public
AsString	public	Access the field's contents as an AnsiString value.
AsUnicodeString	public	Field contents as a UnicodeString.
AsUTF8String	public	Field contents as a UTF8 String.
AsVariant	public	Access the field's contents as a Variant value.
AsWideString	public	Access the field's contents as a WideString value.
AttributeSet	public	Not used: dictionary information.
Calculated	public	Is the field a calculated field ?
CanModify read only	public	Can the field's contents be modified.
ConstraintErrorMessage	published	Message to display if the CustomConstraint constraint is violated.
CurValue read only	public	Current value of the field.
CustomConstraint	published	Custom constraint for the field's value.
DataSet	public	Dataset this field belongs to.
DataSize read only	public	Size of the field's data.
DataType read only	public	The data type of the field.
DefaultExpression	published	Default value for the field.
DisplayLabel	published	Name of the field for display purposes.
DisplayName read only	public	User-readable fieldname.
DisplayText read only	public	Formatted field value.
DisplayWidth	published	Width of the field in characters.
EditMask	public	Specify an edit mask for an edit control.
EditMaskPtr read only	public	Alias for EditMask.
FieldDef read only	public	Fielddef associated with this field.
FieldKind	published	The kind of field.
FieldName	published	Name of the field.
FieldNo read only	public	Number of the field in the record.
HasConstraints read only	published	Does the field have any constraints defined.
ImportedConstraint	published	Constraint for the field value on the level of the underlying database.
Index	published	Index of the field in the list of fields.
IsIndexField read only	public	Is the field an indexed field ?
IsNull read only	public	Is the field empty.
KeyFields	published	Key fields to use when looking up a field value.
Lookup	published	Is the field a lookup field.
LookupCache	published	Should lookup values be cached.
LookupDataSet	published	Dataset with lookup values.
LookupKeyFields	published	Names of fields on which to perform a locate.
LookupList read only	public	List of lookup values.
LookupResultField	published	Name of field to use as lookup value.
NewValue	public	The new value of the field.
Offset read only	public	Offset of the field's value in the dataset buffer.
OldValue read only	public	Old value of the 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.
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.
Visible	published	Should the field be shown in grids.

See all Properties

Methods¶

Member	Visibility	Description
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.
Create	public	Create a new TField instance.
Destroy	public	Destroy the TField instance.
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.

See all Methods

Events¶

Member	Visibility	Description
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.

See all Events

Name	Description
TDataset	Base class for records-based data-access.
TFieldDef	Class to describe one field in a record in a dataset.
TFields	Collection of #fcl.db.TField instances.