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IsNull

property IsNull: Boolean read;

Example​

function HasCustomerReference(const Data: TvxClientDataSet): Boolean;
begin
  Result := not Data.FieldByName('CustomerRef').IsNull;
end;

Usage​

IsNull tests whether the current dataset-state buffer contains no value for the field, preserving the distinction from empty text, zero and false.

  • Test this property before typed access whenever absence has business meaning.
  • Use Clear or assign Variant Null to request null in a pending write.
  • Do not infer database-column nullability or Required enforcement from the current result.

Additional Technical Info​

IsNull tests the field value represented by the dataset's current internal state and active record buffer.

Source-backed behaviour​

TField.GetIsNull calls GetData and returns true when that call reports no value. GetData reads through the owning dataset except during validation, where it can read the temporary validation buffer. Client datasets obtain blank/null state from DSBase. Consequently the answer follows the active dataset state—browse, edit, insert, old/new/current value, filter or calculation—not an independent database query.

Null is different from '', 0, False, an empty blob and Variant Unassigned. Typed getters often return those type defaults for null and therefore discard this distinction. A missing dataset raises; conversion is not required merely to test the buffer. The operation is normally constant-time and side-effect free, although provider/lazy blob details are descendant concerns.

Official RTL references​

Created 2026-07-15