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LinkDataView

function LinkDataView(aDataSet: TvxClientDataSet): TdaQueryDataView;

Example​

procedure ScriptEvent(var Value: variant);
var
  View: TdaQueryDataView;
begin
  View := LinkDataView(Data);
  Value := Assigned(View);
end;

Usage​

LinkDataView rebinds and returns the script execution's reusable query data view for a supplied client dataset.

Parameters

NameTypeDescription
aDataSetTvxClientDataSetLive dataset to assign as the view query. Velox assumes the runtime object is TdaChildSQLClientDataSet.

Returns

The same cached view object on every call made by that script execution. The first call creates on first access it with the script execution as owner.

Additional Technical Info​

LinkDataView exposes a TvxClientDataSet through one reusable TdaSQLQueryDataView owned by the current scripter. It links objects; it does not copy data, run SQL or create a stable view per call.

The example is source-reviewed and was not executed.

Implementation

If FLinkDataView is unassigned, Velox constructs TdaSQLQueryDataView.Create(Self). It then executes an unchecked hard cast and assignment:

TdaSQLQueryDataView(FLinkDataView).Query :=
  TdaChildSQLClientDataSet(aDataSet);

The object reference returned in Result is FLinkDataView.

Aliasing, ownership and lifetime

  • A later call rebinds the one cached view. All variables holding the earlier result still point to that object and now see the later dataset.
  • The dataset remains owned by its original context. The view holds a reference; it does not clone records or schema.
  • The view belongs to the scripter (Self) and is destroyed with it. Scripts must not free it or keep it beyond that context.
  • Closing, moving or rebuilding the linked dataset changes the behaviour observed through the view.
  • The hard cast performs no is check. Passing a different TvxClientDataSet implementation can lead to invalid member access rather than a friendly type error.

Errors and side effects

The method mutates shared binding state and has no exception handler. Allocation and object-access exceptions propagate into the script. It does not log or return nil on failure.

Performance and concurrency

Linking is constant-time after lazy creation, but processing through the view follows the dataset's cursor/query costs. Shared rebinding is not thread-safe and is unsafe for nested consumers requiring different stable datasets.

Related entries

Created 2026-07-15