Mega Code Archive
To use TClientDataset as memory dataset
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Title: To use TClientDataset as memory dataset
As you know starting from Delphi 3, Borland included TClientDataset
component as a database-independent engine.
Generally this component is used for multi-tier environments when you
transfer from server application to client application your data (using
TProvider).
But today I want to show how to use standard TClientDataset component for
memory-dataset without any multi-tiered application.
On any archive you may find some third-party memory datasets:
- TRxMemoryData from freeware RxLib/JVCL (I must say that only TMemoryTable
from RX depends from BDE. TRxMemoryData don't use BDE)
- DevExpress MemData
- KbmMemTable
and a lot of another components
Also some from you use third-party database engines
(Apollo/DBISAM/Halcyon/...) in mode when you don't need a real database.
Exists a lot of task when real database is not required. All what you need
is some temporary dataset.
So I want to show how to use TClientDataset in such mode on small sample.
1. you must create a TClientDataset instance. You may do it in design-time
(simply drop a component on form) or in run-time (for example, in OnCreate
event of your form):
table := TClientDataset.Create(Application);
2. you must add the field defintions:
table.FieldDefs.Add('ID', ftInteger, 0, False);
table.FieldDefs.Add('Status', ftString, 10, False);
table.FieldDefs.Add('Created', ftDate, 0, False);
table.FieldDefs.Add('Volume', ftFloat, 0, False);
3. create a dataset with specified structure:
table.CreateDataset
4. open a dataset
table.Open
5. it's all! Now you may add/edit/delete records, change an order (sort) and
any another action that is available for any dataset.
For example, to add random values to records:
for i := 1 to 100 do
begin
table.Append;
table.FieldByName('ID').AsInteger := i;
table.FieldByName('Status').AsString := 'Code'+IntToStr(i);
table.FieldByName('Created').AsDateTime := Date();
table.FieldByName('Volume').AsFloat := Random(10000);
table.Post;
end;
6. if you want to change an order for records, simply change IndexFieldNames
property. For example, next command will sort your memory dataset by Created
field:
table.IndexFieldNames := 'Created';
7. note that TClientDataset also allow to save memory dataset to file and
load from file:
table.SaveToFile('c:mem.cds');
table.LoadFromFile('c:mem.cds');
A few file formats are supported - internal cds-format and xml-format
Of course, you may use SMImport suite for save/load too - it will work with
such memory dataset without any problems. So you may expand your application
and load data from MS Excel-spreadsheet or MS Access database, for example.
So in such manner you may transfer your data between applications/computers,
update record etc
As example, you may use xml-file instead ini-file and store there any number
of items without limitations on size/value types etc. Just load it to
TClientDataset and navigate thru stored options as thru dataset.
PS: of course, you may also display such memory dataset in DBGrid or print
it using any report engine. Also you may export it in any file format using
SMExport (http://www.scalabium.com/sme)
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