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Brian Wheatley
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 Posted: Mon Jul 12, 2004 12:36 pm Post subject: Implementing IProviderSupport functions |
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Hello,
When I tried using FlashFiler 2.13 with DataSnap I discovered that the
client application could display the data but could not apply the changes
back to the FF2 table. Originally I thought that this was because FF2 would
not return a live data set, but I've since found that this is actually
because the IProviderSupport functions were not implemented. Therefore, I am
implementing the IProviderSupport functions using the BDE components as a
base model.
I've implemented the following functions in the TffDataSet base class:
{ --------- IProviderSupport --------- }
procedure PSEndTransaction(Commit: Boolean); override;
function PSExecuteStatement(const ASQL: string; AParams: TParams;
ResultSet: Pointer = nil): Integer; override;
procedure PSGetAttributes(List: TList); override;
function PSGetQuoteChar: string; override;
function PSInTransaction: Boolean; override;
function PSIsSQLBased: Boolean; override;
procedure PSStartTransaction; override;
function PSUpdateRecord(UpdateKind: TUpdateKind; Delta: TDataSet):
Boolean; override;
{ --------- IProviderSupport --------- }
And the following functions in the TffQuery class:
{ --------- IProviderSupport --------- }
procedure PSExecute; override;
function PSGetDefaultOrder: TIndexDef; override;
function PSGetParams: TParams; override;
function PSGetTableName: string; override;
procedure PSSetCommandText(const CommandText: string); override;
procedure PSSetParams(AParams: TParams); override;
{ --------- IProviderSupport --------- }
With these methods implemented the DataSnap client is now able to update the
FF2 table.
The questions that I have are in regard to the ResultSet parameter of the
PSExecuteStatement method. According to the Delphi help file this is to
allow the PSExecuteStatement method to return the results of a SELECT
statement.
1. Under what conditions will DataSnap send a SELECT statement to the
PSExecuteStatement method?
2. Assuming that I'm dynamically creating a TffQuery (filling in the
SessionName, DatabaseName, SQL, and Params properties), how would I return
this query using the ResultSet pointer?
3. The Delphi help file states that the caller is responsible for freeing
the data set. Am I correct in that I do not have to keep track of the
dynamically created TffQuery since it will be freed by the caller when it is
no longer needed?
I would appreciate any insight that you can offer!
Sincerely,
Brian Wheatley
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Mark Edington (Borland)
Guest
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| Posted: Tue Jul 13, 2004 6:23 pm Post subject: Re: Implementing IProviderSupport functions |
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| Quote: | 1. Under what conditions will DataSnap send a SELECT statement to the
PSExecuteStatement method?
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If there is an error during the update, the resolver will generate a select
query to try and get the current/conflicting values for that row. There may
be other cases too, but that's one I know of for sure.
| Quote: | 2. Assuming that I'm dynamically creating a TffQuery (filling in the
SessionName, DatabaseName, SQL, and Params properties), how would I return
this query using the ResultSet pointer?
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Just return a pointer too it. Take a look at the implementation in
DBTables.pas it uses code like this to create and assign it:
TDataSet(ResultSet^) := TDBDataSet.Create(nil);
Yours should be similar.
| Quote: | 3. The Delphi help file states that the caller is responsible for freeing
the data set. Am I correct in that I do not have to keep track of the
dynamically created TffQuery since it will be freed by the caller when it
is
no longer needed?
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Yes.
Mark
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