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ForceNull

procedure ForceNull

Example​

procedure ScriptEvent(var Value: variant);
begin
  Field.Clear;
  Field.ForceNull;
  Value := Null;
end;

Usage​

ForceNull marks the live field Required so Velox's SQL writer can emit an explicit null, without clearing the field itself.

Errors and side effects

ForceNull itself is a constant-time property assignment. Subsequent Post, validation or SQL generation supplies the material effect and may raise. It does not post, execute SQL or commit. The field is dataset-owned and unsynchronised.

Additional Technical Info​

ForceNull sets the inherited field property Required to true. Despite its name, it does not clear the value or assign Variant Null.

Signature

The example clears the field separately. It is appropriate only when the destination path uses the Velox writer behavior described below; it was source-reviewed and not executed by this documentation workflow.

Exact implementation

Required := True;

Velox's custom daDBExpress SQL generation treats the combination Required = True and a null value as an instruction to write an explicit SQL NULL. A non-null value continues through its normal value path.

This is a product-specific overload of Delphi metadata. Delphi normally defines Required to mean that a nonblank value is required. Standard dataset posting/required-field validation can therefore reject the same null value with an EDatabaseError. Confirm the destination adapter before using this helper; it is not a portable way to set null.

State and lifecycle

  • The flag remains true on the shared field object until code changes it or the dataset rebuilds its fields.
  • It affects later work on the same field, not only the current assignment.
  • Calling it on a non-null field changes only metadata; it does not schedule a future null.
  • Calling Clear without ForceNull sets null but may let the Velox SQL writer omit the column rather than explicitly assigning SQL NULL, depending on that writer's update rules.

External references

Created 2026-07-15