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AsVariant

property AsVariant: Variant read write;

Example​

procedure CopyOptionalValue(const Source, Target: TvxClientDataSet);
begin
  Target.FieldByName('Reference').AsVariant :=
    Source.FieldByName('Reference').AsVariant;
end;

Usage​

AsVariant reads or writes the field as a Variant, preserving explicit database Null where supported and converting other dynamic values through field rules.

  • Use VarIsNull to test database null; do not compare a Variant directly with Null.
  • Prefer typed As... properties when the target type is known and null is handled separately.
  • Treat Unassigned, Null, empty string and numeric zero as four different states unless the mapping contract deliberately combines them.

Additional Technical Info​

AsVariant provides the generic dynamically typed field value. Value is an alias of the same getter/setter on TField.

Source-backed behaviour​

Base TField.GetAsVariant raises; concrete descendants return a Variant appropriate to their data type and normally return Null for a null database value. On assignment, base SetAsVariant treats VarIsNull(Value) specially and calls Clear. Other values are delegated to the descendant's SetVarValue; Delphi variant-conversion errors are translated to a field-value database error. Unassigned/Empty is not the same test as Null and may be rejected or converted by the descendant.

The write requires a client-dataset write state and can trigger OnValidate, DSBase constraints and field-change events. Variants reduce compile-time type checking and can hide precision/encoding conversions. Blob or interface-valued descendants may use specialised Variant representations.

Official RTL references​

Created 2026-07-15