Delphi - ClientDataSet - validating data

Question

I have an application in Delphi 7 which is using a clientdataset, and make several operations on it. ClientDataSet is linked to an Intraweb Grid.

I make an insert or an edit on the ClientDataSet. How can I verify the data introduced in the clientdataset for each field? I can not verify the input from the user on the webform, so I must make validation using ClientDataSet events.

LE: I want to validate data when the user make the input. Not at the onbeforepost event. So, I put the clientdataset in the edit/insert. User make an input in the grid, and I want to validate the data for that row in the clientdataset like in the image bellow:

enter image description here

first column is string, second is integer, the third one is also an integer. Now, I want to validate the third column after the user make the input. This validation must be done (if it is possible), only by using clientdataset events/hacks.

score 3 · Accepted Answer · answered May 23 '11 at 10:11

3

You should handle TClientDataset BeforePost event, and if data is not valid use abort method

answered May 23 '11 at 10:11

Antonio Bakula

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Or maybe better, raise a proper exception to be shown to the user. – Ondrej Kelle May 23 '11 at 10:13
I saw this question - http://stackoverflow.com/questions/838546/delphi-canceling-a-tdataset-post-in-an-onbeforepost-event. thanks.+1 – RBA May 23 '11 at 10:17
@RBA in that case the user is asked to confirm to save changes. You want a silent exception there because the user already answered a question. In this case, the user is posting an update and would probably be surprised/confused if it's ignored without an error message. – Ondrej Kelle May 23 '11 at 10:23
I modified the question to be more explicit. – RBA May 23 '11 at 10:30
why not DataSet.Cancel? – nurettin Apr 29 '16 at 13:58
BeforePost will not always be called - for example if the input value exceeds the field type boundaries (for example '10.000' in for a Numeric 4 field) – mjn42 Oct 24 '17 at 11:57

score 3 · Answer 2 · 2011-05-23T11:14:39.887

TField has an OnValidate event for that purpose. It has also a CustomConstrain property that can use a SQL like syntax for constraints. DefaultExpression will let you select a value if no value is given. These are usuful for single-field validation. If you need more complex checks across more than one field, then you have to use dataset or datasource events.

Anyway, if the Intraweb grid sends the server whole records and not single fields edits, you may not validate fields as they are entered in the grid but adding code client side.

score 1 · Answer 3 · answered May 23 '11 at 10:51

If you want a field based validation, you can handle the OnDataChange event of the TDatasource connecting the grid to the dataset. This will be triggered whenever a field has been changed by the user. You should be aware that it will also be triggered in some other situations.

Delphi - ClientDataSet - validating data

3 Answers3