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Value

property Value: Boolean read write

Example​

procedure ScriptEvent(var Value: variant);
var
  Flag: TBooleanField;
begin
  Flag := TBooleanField(DATA_Self.FieldByName('Enabled'));
  if Flag.IsNull then
    Value := Null
  else
    Value := Flag.Value;
end;

Usage​

Reads or writes the current record's Boolean value while collapsing a null read to False.

Behaviour

  • Reading uses the current dataset record at the instant of the call.
  • Writing replaces null or the prior value with a non-null Boolean in the current record buffer.
  • A write requires an active writable field and the dataset's edit, insert or equivalent state.
  • The property does not call Post, apply updates, execute SQL or commit a transaction.

Important usage notes

  • Null and False are observationally identical through Value alone. IsNull plus Value must be treated as a two-operation snapshot and can become stale if nested/concurrent code moves the cursor.
  • The field's text can use custom phrases, abbreviations and locale rules, but Value accepts only the script Boolean type.
  • A direct class cast does not validate a field definition; casting a non-Boolean runtime field is invalid.

Errors

Inactive dataset, invalid current record, read-only/calculated field, wrong edit state, invalid cast and dataset buffer/event errors can raise. There is no automatic edit, rollback or error translation in the Velox helper.

Usage notes

Use Value for Boolean logic and DisplayValues only for presentation/string interchange. Explicitly decide how null should map before assigning the result to a non-nullable Boolean variable or destination field.

Additional Technical Info​

Value reads or writes the typed Boolean value on the owning dataset's current record. A read returns False for both stored False and null, so check IsNull first when the distinction matters.

The example preserves nullable Boolean semantics for a fictional field. It is source-reviewed and was not executed by the documentation workflow.

The property is equivalent to this class's inherited AsBoolean path. DisplayValues does not affect it.

Implementation

The Velox runtime helpers directly call native TBooleanField.Value. On read, GetAsBoolean asks GetData for the current field buffer and explicitly returns False when no non-null value is available.

On write, SetAsBoolean normalises False to zero and True to one in a two-byte WordBool buffer, then calls the dataset field's SetData. The write is a typed Boolean operation; it does not parse text or consult locale/display phrases.

Side effects

Assignment marks the current field/record modified through the owning dataset's normal event path. It does not change DisplayValues or any other record.

Performance and concurrency

The value is fixed-size and access is normally constant time. The dataset cursor and record buffer are shared mutable state without an atomic IsNull-plus-Value API; coordinate access when a dataset can be reused or navigated by nested code.

Related entries

  • DisplayValues controls only the field's string/display conversion.

External references

Created 2026-07-15