TADMetaInfoQuery.Indexes Property

Lists all client indexes that apply to the dataset.

Group

Links

TADMetaInfoQuery Class, TADMetaInfoQuery Members, uADCompClient Namespace, Example 1, Example 2, published, See Also

Use Indexes to define client side data views on the dataset records. Indexes are a collection of the TADIndex objects, each of them defines optional:

Sorting by fields (Fields, CaseInsFields, DescFields, Options).
Sorting by expression (Expression, Options).
Records filter (Filter, FilterOptions).
Records distinction flag (Distinct).

The individual indexes are not just the sort and filter definitions. AnyDAC maintains a consistent view on the data for each active index, while application fetches data or edits data. That creates additional overhead, but allows to switch between indexes without delays.

To make a view current, set it Selected property to True or dataset IndexName property to the view name. Note, the view must have Active = True to be maintained.

Dataset maintains Indexes views, when IndexesActive is True. When an application needs to perform batch updates to dataset, then set IndexesActive to False before updates, and return to original value after updates. Also see BeginBatch / EndBatch methods.

Setting IndexFieldNames does not add a TADIndex object to Indexes collection. Defining IndexDefs before dataset opening, will clear Indexes and fill them using IndexDefs information. So, there are two alternative ways - use IndexDefs or use Indexes. We suggest to use Indexes, as it is more flexible.

Some of the navigation methods, like a Locate / Lookup / SetRange are using indexes to optimize their operations.

The sorting and filter expressions in Indexes supports syntax compatible with:

BDE data access components;
TClientDataset;
Oracle 8 (not for 100%).

Syntax

property Indexes: TADIndexes;

See Also

Sorting Records, Writing Expressions, IndexDefs, IndexesActive, IndexFieldNames, IndexName, BeginBatch, EndBatch

Example 1

with ADMemTable1.Indexes.Add do begin
  Name := 'by_name';
  Fields := 'NAME;DT';
  Active := True;
end;
with ADMemTable1.Indexes.Add do begin
  Name := 'by_payments';
  Expression := 'sum(sal + bonus)';
  Filter := 'dep_id is not null;
  Active := True;
end;
ADMemTable1.IndexesActive := True;
ADMemTable1.IndexName := 'by_name';

Example 2

See AnyDAC\Samples\Comp Layer\TADQuery\Indices demo for details.

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