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Open

procedure Open;

Example​

procedure EnsureOpen(const Data: TvxClientDataSet);
begin
  if not Data.Active then
    Data.Open;
end;

Usage​

Open activates the dataset and, for TvxClientDataSet, materialises provider data into its client buffer.

  • Opening can execute external SQL/provider work and materialize an unbounded result; constrain the query before opening.
  • Do not infer that constraints or change logging protect later script edits in normal TvxClientDataSet mode—they are explicitly disabled.
  • Repeated Open while already Active is a no-op through the property equality check.

Additional Technical Info​

Open is declared by hidden ancestor TDataSet and is normally used through a visible descendant such as TvxClientDataSet. It is equivalent to assigning Active := True.

Source-backed behaviour​

Base TDataSet.Open only sets Active. The modified active setter runs before-open, opens/initializes the descendant cursor and fields/buffers, enters browse state and runs after-open, cleaning up back to inactive on incomplete open.

TvxClientDataSet.SetActive(True) attaches its provider when an SQL connection exists, then uses TCustomClientDataSet to fetch. Its constructor sets FetchOnDemand=False and PacketRecords=-1. After a normal non-edit-mode open it sets LogChanges=False, disables constraints, detaches the provider and closes the owned SQL dataset; the client rows remain in memory.

Close deactivates and releases buffers. RecordCount describes materialized count.

Official RTL references​

Created 2026-07-15