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TClientDataset as memory dataset (Views: 101)


Problem/Question/Abstract:

How to use TClientDataset as memory dataset

Answer:

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.

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