What I'm trying to achieve to to insert/copy records from a tClientDataSet to a database table(Database is Sybase ASA).
I also have a form with a cxgrid on it which I can see the records from the cds, so I know there are records in it.
At the click of a button I do the following:
with dmData.cds do
begin
Close;
Open;
First;
while not (EOF) do
begin
dmData.qry1.Open;
dmData.qry1.Insert;
dmData.qry1.FieldByName('field1').AsString := dmData.cds.FieldByName('field1').AsString;
dmData.qry1.FieldByName('field2').AsString := dmData.cds.FieldByName('field2').AsString;
dmData.qry1.FieldByName('field3').AsString := dmData.cds.FieldByName('field3').AsString;
dmData.qry1.Post;
Next;
end;
end;
I don't get any errors after this is done but when looking in the database table there are no records inserted.
I don't know what I'm doing wrong, any help would be much appreciated.
It seems you are trying to do the work that TClientDataSet does for you. In order to have all this working you need three components:
An instance of a dataset able to talk to your data server, already configured to do so
An instance of TDatasetProvider referencing the previous dataset, by using the Dataset property
An instance of TClientDataSet referencing the previous provider, by using the ProviderName property
After all the records in TClientDataset (CDS) were updated, you call ApplyUpdates(0) to send them to the provider. When you call this method, the CDS builds a data pack named Delta with the records that have to be persisted and send it to the provider.
The provider does not know how to persist the records existing in the Delta, so it coworks with the dataset you assigned to it. For each record in the Delta, the corresponding operation is executed over the dataset, so the data server will start receiving commands.
At the end, the provider notifies the CDS that everything was alright (this is named reconciliation), eventually returning keys generated during the insert operations. Those keys will appear in the CDS.
After all that, the status of the changed records will be cleared, in order to report no pending changes (an important something that your code was not doing).
I recomend you read more about DataSnap to really master it. The Delphi help has enough information on that.
Related
The TSQLQuery class is unidirectional, so for it to be used as a source for a data-bound TDBGrid, a TClientDataSet needs to be linked between the TSQLQuery and the TDataSource that the TDBGrid is bound to.
I can connect the TSQLConnection and make the TSQLQuery active at design-time, with specified params, and then I can right-click on the CDS and choose the "Assign Local Data..." option to have it grab the data from the TSQLQuery, which then appears in the TDBGrid via the linked TDataSource.
The amount of time between choosing "Assign Local Data..." and the data actually appearing in the grid is very short, so I am looking for the way to replicate this at run-time.
Supposedly, I can set the Data property of the CDS to the Data of the source, but a TSQLQuery has no Data property. There was a post about using a provider, but
DataSetProvider1.DataSet := SQLQuery1;
ClientDataSet1.Data := DataSetProvider1.Data;
throws an access violation,
I did implement the data copy by looping through the TSQLQuery and appending the records to the TClientDataSet, but that was a lot slower than the "Assign Local Data...".
[Edit 1]
All the components I need are hooked up at design-time, and I can make the TSQLConnection active, then the TSQLQuery, then the TClientDataSet and the TDBGrid displays the data from the parameterised query defined in the TSQLQuery.
In the OnChange event of a TComboBox, I need to refresh the query using a different parameter and have the grid show the relevant results, so I Close the TSQLQuery, change the ParamByName value, Open the TSQLQuery and then call ClientDataSet1.Last to highlight the last row in the grid.
That gives me a "Cannot perform this operation on a closed dataset" error, so I use
ClientDataSet1.Active := true;
but that throws an "Access Violation".
All the examples I can find are all about dropping components onto a form, linking them together, and they work. Well, yes they do, but I need to change properties in code at run-time and still have it work, which it just refuses to do.
This is really beginning to frustrate me.
[Edit 2]
So I followed the example on the Embarcadero site for building a VCL Forms dbExpress Database Application, substituting my database connection details for the Interbase one the example uses.
http://docwiki.embarcadero.com/RADStudio/Tokyo/en/Building_a_VCL_Forms_dbExpress_Database_Application
In the designer, everything looked fine and the grid was showing the results from the query, but when I went to run it using F9, I was getting an "Access Violation" thrown from within TCustomClientDataSet.InternalCheck.
Turns out this is a known MIDAS.DLL versioning problem and can be resolved by including MIDASLib in the uses clause of the form. It is just unfortunate that the Datasnap.DBClient code is still throwing Access Violations instead of proper messages, especially since this problem was reported in 2013.
You can use this code. Just change TUniConnection and TUniQuery to what You are using:
Procedure CdsAssignTable(aTableName:String; aCds : TClientDataSet; aCon
:TUniConnection );
Var
aQUery : TUniQuery;
aProvider : TDataSetProvider;
begin
if aCon=Nil then raise Exception.Create('aCon=Nil');
if aCds=Nil then aCds:=TClientDataSet.Create(aCon.Owner);
aQUery:=TUniQuery.Create(Nil);
aQUery.SQL.Text:='select * from '+aTableName;
aQUery.Connection:=aCon;
aQUery.Open;
aProvider:=TDataSetProvider.Create(Nil);
aProvider.DataSet:=aQUery;
aCds.Data:=aProvider.Data;
FreeAndNil(aProvider);
FreeAndNil(aQUery);
End;
I have a TClientDataSet which stores data coming from a medical instrument. This client dataset is linked to a grid to display data in real time. My problem is, when the user is editing the data, and the instrument sends a new packet, the data which the user has modified but not yet posted is lost because I only can get a TBookmark on current record, append the new record, and then goto the saved bookmark (which is sometimes not the correct record, apparently due to the new record). I can check dataset's State, Post if necessary, and then set the State afterwards, I'm looking for a way to update data in client dataset without affecting its State. Is this even possible?
Clone the dataset and modify the data on the clone.
A document on it by Cary Jensen is here: http://edn.embarcadero.com/article/29416
Basically you need something like
var
lEdDataset: TClientdataset;
begin
lEdDataset := TClientDataSet.create(nil);
try
lEdDataset.CloneCursor(SourceDataSet, True**);
StoreMedDeviceRecord(lEdDataset);
finally
lEdDataset.free;
end;
** You'll need to read the documentation on the True/False settings and decide what you actually need (I can't remember off-hand)
I have been asked by my company to update the reporting functionality of a paticular application written in delphi and using Quick reports to use FastReports instead.
The current implementation pulls all the data out of the database, does a lot of work to organise and calculate the required data for the reports and stores all this in several different objects. The Quick Report OnNeedData events are then used to fill out the bands until there is no more data (signified by setting MoreData = false)
The problem I'm having is Fast Reports seems to need a band to be connected to an actual data source, which I don't have. Also fastReports doesn't seem to have an event similar to OnNeedData.
Is there anyway to fill out the values of a data band in code and have it print again until all data is printed without connecting the band to a dataset?
I appologise for the vagueness of this question, I am very new to reporting software and any suggestions of where to go and what to look at would be greatly appreciated.
Fast reports use a intermediary object descending from _TFrxDataSet to connect the report engine which the data it prints.
To connect a report to a data source managed by the program itself, you use a TfrxUserDataSet component, which let's you see a data set inside the report, but you manually specify the column names in the Fields (TStrings) property and manage and supply values programatically writing event handlers for the following events:
OnCheckEOF is functionally equivalent to the OnNeedData, if there's no more to print, you set the EOF var parameter to true
OnFirst you do whatever you have to do to start walking for the data.
OnGetValue and OnNewGetValue you provide values for each of the different columns of the current row
OnNext, OnPrior you move your current row one next or one prior position.
As you see, the row/column concept (a DataSet) is used to provide the data to the report, but you can pull your data from any structure you use to store the result of your calculations (lists, arrays, or any other object/structure/file etc.)
Inside the report, you link the band to this logical DataSet and you use standard components to print the column values of this DataSet.
If you already have the data in a DataSet, for example a in-memory DataSet after your calculations, better use a TfrxDBDataset to directly bind your report to that source of data.
you can use TfrxUserDataSet.There is a demo named 'printstringlist' under folder 'demos'.
In our project we have implemented our own class inherited from TfrxCustomQuery. This new query class simply redirects its SQL statements to our application' internal query engine. We registered this new class in FastReport palette (used frxDsgnIntf.frxObjects.RegisterObject* for FR version 3 and 4) and now it is used in all our report templates instead of TfrxADOQuery or other built-in dataset classes.
Here is another alternative:
I've been using FastReport for years. I sometimes run into a similar situation. For offline tabular reports I use an in-memory dataset. I purchased DevExpress long time ago and so I have TdxMemData. But even without it, you should be happy using the TClientDataset component.
Besides that, the TfrxUserDataset is an alternative which I use when showing lists of objects.
There is a possibility to do it like this, it is slow though ,
Code:-
var
FRX: TfrxReport;
procedure NewPage;
begin
MyPage := TfrxReportPage.Create(FRX);
MyPage.CreateUniqueName;
MyPage.PaperSize := DMPAPER_A4;
end;
procedure ...(AText: string);
var
frMemo : TfrxMemoView;
begin
frMemo := TfrxMemoView.Create(MyPage);
frMemo.CreateUniqueName;
frMemo.Text := AText;
end;
Regards
Herman
I have a form with a query, a dataset, an editable dbgrid and an updatesql component. When I need to save the changes made in the dbgrid, I call this procedure:
procedure TEditCardDetailForm.SaveChanges;
begin
Database1.StartTransaction;
try
Query2.ApplyUpdates;
Database1.Commit;
except
Database1.Rollback;
raise;
end;
Query2.CommitUpdates;
end;
However I want the changes to be applied automatically to the database when I press Enter or go to another row after editing a cell in the dbgrid - the way it is done when I use a TTable component. Is there a way to do it?
If I understand it right (please correct me if not) you have a TQuery with CachedUpdates set to true, but want it to behave as if it would not be using cached but immediate updates. If that is the case the way you have set up your TQuery contradicts your desired behaviour. Cached updates are to be "held" on the client side until you decide to manually post them to the database by using ApplyUpdates.
In case you can set CachedUpdates to false, you only need to do following:
Link the TUpdateSQL to the TQuery via its UpdateObject property.
Write the insert, update and delete statements and assign them to the InsertSQL, ModifySQL and DeleteSQL properties of the TUpdateSQL.
I guess you already have done these two things, so putting CachedUpdates to false should do it.
You can find more information on Cached Updates for Delphi 5 here.
HTH
You have two scenarios to handle here:
save changes when changing the grid row
save changes when changing the grid column
The first one is easy to implement by calling your SaveChanges procedure in the AfterPost event of the underlying dataset (query2, a TClientDataSet?).
For the second one you only have to call query2.Post after the column has changed. This can be done in the OnDataChange event of the datasource. Make sure to check for Field <> nil and the dataset being in insert or edit mode before calling post.
I have a (Firebird) DB. For most of my tables I have a trigger which fires before insert which will create the Primary Key (PK) for me via a generator as well as write to the newly inserted records a Created Date value and a Created By value. I also have an update trigger which writes to an Updated Date field and an Updated By field.
eg (Client is a table in my DB):
create trigger t_client_id for client
active before insert
as begin
new.client_id = gen_id(gen_client_id, 1);
new.created = current_timestamp;
new.created_by = current_user;
new.lock_vn = 1;
end ^
create trigger t_client_update for client
active before update
as begin
new.updated = current_timestamp;
new.updated_by = current_user;
end ^
When I apply updates thru my ClientDataSet (CDS) - which are attached to remote TDataSetProviders via a TDSProviderConnection, how can I "retrieve" these generated values? If I edit an existing one (which will in turn call the t_client_update trigger, calling RefreshRecord will get the updated and updated_by fields. However, the Doco says to use that method cautiously, so that may not be the correct way to achieve this. I call it straight after I've called ApplyUpdates(-1).
The CDS I use only contains the one record I am attempting to Edit. For a New record, the CDS is in dsInsert mode. Everything is written to the DB ok so I just need to get this new data back out again. I have also tried using a CDS which contains ALL records in the table too to see if it was any simpler but didn't make any difference - unsurprisingly. The reason I need this information is simply to show to the user in DB Aware controls these values. They are read only.
I could call a Get on the record I guess when editing an existing record, using the PK, but that won't help for an Insert as I don't know what the new PK is.
Example of where I attempt to ApplyUpdates to my CDS (actDSSave is a TDataSetPost action)
dsState := actDSSave.DataSource.DataSet.State;
DoApplyUpdates(-1);
if dsState = dsEdit then
TClientDataSet(actDSSave.DataSource.DataSet).RefreshRecord;
I am using TIBQuery for my dataset attached to the remote DataSetProvider. This query SQL is a simple select * from client where client_id = :client_id. I have tried associating this query with a TIBUpdateSQL too as well as trying to set poAutoRefresh to true in the DataSetProvider.
So is it possible to obtain these Trigger generated values this way or do I need to approach it in a different way? Another way I can think of, is to create stored procedures which do CRUD against each table and use that instead (with appropriate in/out params to return this new data) but hopefully I don't have to go down that track. Hopefully I have provided sufficient info here to explain and replicate the issue.
Thanks
EDIT
Realised in above, DoApplyUpdates(-1) is my own method. It's implementation at the moment is simply:
FdatCommon.cdsClient.ApplyUpdates(MaxErrorCount);
FdatCommon is a TDataModule containing my CDS.
You simply can't get "generated" values without new requery (RefreshRecord) of data after Post.
It's because triggers runs on server side when you call ApplyUpdates, but TClientDataSet does not refresh by default posted record. For example other libraries FIBPlus have an option to do it automatically.
About inserts, TIBDataSet have GeneratorField property. Using it, dataset query and increment generator value separatelly before insert. So you will have PK values after post even on inserts. But avoid using it again in trigger.
MIDAS (TClientDataSet) is a great library, but his general / universal architecture loose DB specific features (such as retriving values from inserts) compared to dedicated libraries for specific DBMS, such as FibPlus. By the way I saw TpFIBClientDataSet. It work in conjunction with TpFibDataSet.