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AfterMap (Field)

The field-level AfterMapEvent performs the final scripted transformation for one destination field. Its Value starts from the field value produced by normal mapping and the field's OnMap event; assigning it writes the final value back to that field.

Syntax​

procedure AfterMapEvent(var Value: Variant);
begin
  if not (VarIsNull(Value) or VarIsEmpty(Value) or VarIsClear(Value)) then
    Value := Trim(VarToStr(Value));
end;

The source-reviewed example safely trims a non-null, assigned value. Whether text conversion is appropriate depends on the destination field type.

How it works​

The view map first runs the OnMap pass across all fields. It then makes a separate AfterMap pass across all fields. For an eligible field, RunFieldScripts(False) reads Field.Value into a local Variant, calls the field map's AfterMap delegate and assigns the resulting Variant back to Field.Value.

The delegate is compiled lazily using the field map's Source, Dest and Global Script context. It has the same procedure AfterMapEvent(var Value: Variant) shape as record-level AfterMap, but it is owned by a TvxFieldMap and receives a field value rather than the record-control Boolean.

Value and side effects​

The input is the current destination field value after its OnMap logic. A change to Value is written to the field after the script returns. The field setter can perform type conversion, validation and dataset modification. A value unsuitable for the field type can fail during the assignment back even when the script itself completed.

Errors​

The entire read–execute–write sequence is inside a field-mapping exception handler. An exception is logged as an inability to map the named field and includes the field's OnMap script in the log context. This is a current diagnostic quirk: an AfterMap failure can be accompanied by the OnMap script text rather than the AfterMap source. The function returns the current log status, which can stop later fields.

Performance and ordering​

Each eligible field invokes its own event synchronously. All field OnMap scripts run before any field AfterMap scripts; this lets a field-level AfterMap read other destination fields after their initial mapping. Field AfterMap completes before the record-level AfterMap event and before detail views.

Edge cases and quirks​

  • Do not use Value as a record-control Boolean here; it is the field's actual Variant value.
  • Some key/linked field types use specialised mapping paths and may not execute the same scripted phases as ordinary fields.
  • Assigning Null, an empty string or zero has different consequences based on field type, required state and downstream posting rules.
  • The sidebar places field AfterMap last to distinguish it from record-level AfterMap, but its runtime call occurs earlier.
  • Cancellation stops remaining field scripts.
  • AfterMap (Record) — record-control event that follows the field pass.
  • Testing values — Variant state checks before conversion.
  • Datasets — field assignment and posting behaviour.