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Dataset

Dataset = TvxClientDataSet

Example​

procedure ReadCustomer(const Source: Dataset; var Value: Variant);
begin
  if Source.Find('CustomerCode', 'ABC') then
    Value := Source['CustomerName'].AsString
  else
    Value := Null;
end;

Usage​

Aliases TvxClientDataSet without copying its Velox-provided records, schema, cursor, or mutable state.

Identity, cursor and lifetime​

Assigning a Dataset variable copies only the object reference. Both variables see the same fields, rows, indexes, filter/edit state and current record. A Find, navigation, load, delete, sort/index or close operation through either reference can move or rebuild the shared cursor. A borrowed field object also follows that current record and can become invalid when the schema or buffers are rebuilt.

The normal DATA*, view and query objects supplied to a script are created and owned by Velox. Do not call Free on them. Scripts cannot construct a TvxClientDataSet directly, and the alias does not add one. If a future function returns a Dataset, that function's page must define whether the object is borrowed, Velox-provided or transferred; the alias alone cannot answer ownership.

Class references can be nil. A nil value has no dataset state, and calling a member through it fails. Check the producer's nullable contract or use Assigned when nil is possible.

Data and transaction boundary​

The object is an in-memory client-dataset instance. Assignment does not duplicate records or create a stable snapshot. Ordinary edits affect the shared in-memory instance, while external database/file persistence depends on the surrounding Velox flow or an explicit operation. The alias neither opens the dataset nor commits a transaction.

One instance is mutable and unsynchronised. Keep it within its owning action/thread, snapshot scalar values before calls that can navigate, and prefer business keys over transient record positions.

Additional Technical Info​

Dataset is installed during every Velox script compilation with AddTypeCopyN('Dataset', 'TvxClientDataSet'). The modified PascalScript compiler resolves the target and creates a type link to it. This is compile-time identity: it is not a wrapper, subclass, dataset factory, packet conversion or copy operation.

The alias exposes exactly the TvxClientDataSet object reference accepted by the compiled function or property. All visible Velox-specific members, inherited dataset members, and their implementation quirks are unchanged.

Related Code Library entries

External references

Created 2026-07-15