BorlandTalk.com Borland discussion newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Object reference          BorlandTalk.com Forum Index -> Delphi Databases (dbExpress) View previous topic :: View next topic   Author Message Martin Guest Posted: Mon Jan 02, 2006 6:24 am    Post subject: Object reference Hi, I have a TSimpleDataSet (D7, kind of a ClientDataSet) and I create an object for each of the records in it. Whilst doing this, I want to store the corresponding object reference in my DataSet. I tried to add an extra field for this, but that gets messy. I tried the Fields[0].Tag, but this is not a per record property. Any ideas? /M Back to top Bill Todd Guest Posted: Mon Jan 02, 2006 12:42 pm    Post subject: Re: Object reference Martin wrote: Quote: Hi, I have a TSimpleDataSet (D7, kind of a ClientDataSet) and I create an object for each of the records in it. Whilst doing this, I want to store the corresponding object reference in my DataSet. I tried to add an extra field for this, but that gets messy. I tried the Fields[0].Tag, but this is not a per record property. Any ideas? /M Add a computed field to the SELECT statement that loads the CDS. SELECT F1, F2, 1000000 AS PTR FROM SOMETABLE -- Bill Todd (TeamB) Back to top Martin Guest Posted: Mon Jan 02, 2006 1:03 pm    Post subject: Re: Object reference Hi Bill As I wrote, I tried just that - but it tends to get messy when you issue ApplyUpdates since the extra field cant be found. My present circumvent is to manage a parallell TList with pointers, but this is not at all a preferred solution. /M "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: Martin wrote: Hi, I have a TSimpleDataSet (D7, kind of a ClientDataSet) and I create an object for each of the records in it. Whilst doing this, I want to store the corresponding object reference in my DataSet. I tried to add an extra field for this, but that gets messy. I tried the Fields[0].Tag, but this is not a per record property. Any ideas? /M Add a computed field to the SELECT statement that loads the CDS. SELECT F1, F2, 1000000 AS PTR FROM SOMETABLE -- Bill Todd (TeamB) Back to top Bill Todd Guest Posted: Mon Jan 02, 2006 10:24 pm    Post subject: Re: Object reference You must set the pfInUpdate ProviderFlag for the field to False. To do this change the ProviderFlags property of the field object of the source dataset (the one the DSP is connected to) not the ClientDataSet. Also read the on-line help for the TField.ProviderFlags property. -- Bill Todd (TeamB) Back to top Martin Guest Posted: Tue Jan 03, 2006 11:46 am    Post subject: Re: Object reference ReHi, Are you sure this works? I connected TSQLDataset->TDatasetProvider->TClientDataset and set the CommandText of the TSQLDataset to 'Select t.*, 0 ObjPtr from MyTable t' The data shows fine, but the Fields array of the TSQLDataset is empty, and hence no ProviderFlags property can be set. I can set it for the ObjPtr field on the TClientDataset, but with no effect (as implied by you). /M "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: You must set the pfInUpdate ProviderFlag for the field to False. To do this change the ProviderFlags property of the field object of the source dataset (the one the DSP is connected to) not the ClientDataSet. Also read the on-line help for the TField.ProviderFlags property. -- Bill Todd (TeamB) Back to top Bill Todd Guest Posted: Tue Jan 03, 2006 1:06 pm    Post subject: Re: Object reference Martin wrote: Quote: The data shows fine, but the Fields array of the TSQLDataset is empty, and hence no ProviderFlags property can be set. Did you instantiate the field objects for the SQLDataSet using the fields editor? If you do, then you can set the ProviderFlags property at designe time. -- Bill Todd (TeamB) Back to top Martin Guest Posted: Tue Jan 03, 2006 1:22 pm    Post subject: Re: Object reference No I didnt, and I can't. This is a generic routine in an anscester class meant to enumerate objects from nomerous different tables in different descendent classes. Persistent fields are not an option. /M "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: Martin wrote: The data shows fine, but the Fields array of the TSQLDataset is empty, and hence no ProviderFlags property can be set. Did you instantiate the field objects for the SQLDataSet using the fields editor? If you do, then you can set the ProviderFlags property at designe time. -- Bill Todd (TeamB) Back to top Bill Todd Guest Posted: Tue Jan 03, 2006 2:24 pm    Post subject: Re: Object reference Martin wrote: Quote: No I didnt, and I can't. This is a generic routine in an anscester class meant to enumerate objects from nomerous different tables in different descendent classes. Persistent fields are not an option. Then you will have to set the ProviderFlags property in code. -- Bill Todd (TeamB) Back to top Martin martin_gbg_hotmail Guest Posted: Wed Jan 04, 2006 10:57 am    Post subject: Re: Object reference "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: Martin wrote: No I didnt, and I can't. This is a generic routine in an anscester class meant to enumerate objects from nomerous different tables in different descendent classes. Persistent fields are not an option. Then you will have to set the ProviderFlags property in code. -- Bill Todd (TeamB) Read earlier posts and you will see that this is what I tried to do - but since the Fields array is empty it is not possible. Field objects are not created in the source dataset, merely in the client dataset. Well, I guess I will have to settle for a maintaned parallell TList of object pointers, but it is not a preferred solution. Thanks Bill Back to top Bill Todd Guest Posted: Wed Jan 04, 2006 12:52 pm    Post subject: Re: Object reference "Martin" martin_gbg_hotmail.com wrote: Quote: Read earlier posts and you will see that this is what I tried to do - but since the Fields array is empty it is not possible. Field objects are not created in the source dataset, merely in the client dataset. That is not correct. If you do not instantiate field objects at design time they are created dynamically at runtime by every descendent of TDataSet. This has been true since Delphi 1.0. You can set the ProviderFlags property or any other property of the field objects in the AfterOpen event handler. -- Bill Todd (TeamB) Back to top Martin Guest Posted: Wed Jan 04, 2006 1:57 pm    Post subject: Re: Object reference "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: That is not correct. If you do not instantiate field objects at design time they are created dynamically at runtime by every descendent of TDataSet. This has been true since Delphi 1.0. You can set the ProviderFlags property or any other property of the field objects in the AfterOpen event handler. Here it is again: I connected TSQLDataset->TDatasetProvider->TClientDataset and set the CommandText of the TSQLDataset to 'Select t.*, 0 ObjPtr from MyTable t' I then set the Dataset.Active property to true. TSQLDataset.Fields.Count = 0 TClientDataset.Fields.Count=11 Maybe I am missing something here. /M Back to top Bill Todd Guest Posted: Wed Jan 04, 2006 7:53 pm    Post subject: Re: Object reference Sorry. I misunderstood what you said. There is no solution that I know of in that case. If you do not instantiate the field objects for the SQLDataSet at design time the DSP has no way to look at the ProviderFlags when it is generating the SQL statements to apply inserts and updates. -- Bill Todd (TeamB) Back to top Martin Guest Posted: Thu Jan 05, 2006 5:57 am    Post subject: Re: Object reference "Bill Todd" <no (AT) no (DOT) com> wrote: Quote: Sorry. I misunderstood what you said. There is no solution that I know of in that case. 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