Database Query and other components inside complex Delphi component
Hi! I am trying to develop Delphi DB component for displaying and editing customer data. Many tables (like, carts) in my database references customer using foreign key (like carts.fk_customer) and users want to see a lot of data about customer in diferent forms. So - I am planning to make the component (apparently - derived from TPanel) with the usual properties - DataSource, DataField (for FK_CUSTOMER) and this component should process the changes of its data field (usually fk_customer) by reading addional d ata from the query (component has DataSource property, so, this is possible to find the transaction of the DataSource.DataSet and assign this transaction to the component's query) inside this component and displaying in additional fields on this component. I just wanted to chek whether this is the right solution? Actually I am also confused which component - DB component (maybe TDataLink is not necessary in this case) or the usual non-DB component (apparently TDataLink is required in this case) - should I use for displaying and providing editing capabilities to the DataField. For the remaining fields in my component (for data from the customers table - like first_name, middle_name, last_name, contact information (multiple addresses) I can certainly use the usual database components, I guess...
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Tom
5/7/2012 2:23:19 PM
public.delphi.vcl.writing
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Tom Rhodes wrote: > Hi! > > I am trying to develop Delphi DB component for displaying and editing > customer data. Many tables (like, carts) in my database references > customer using foreign key (like carts.fk_customer) and users want to > see a lot of data about customer in diferent forms. So - I am > planning to make the component (apparently - derived from TPanel) > with the usual properties - DataSource, DataField (for FK_CUSTOMER) > and this component should process the changes of its data field > (usually fk_customer) by reading addional d ata from the query > (component has DataSource property, so, this is possible to find the > transaction of the DataSource.DataSet and assign this transaction to > the component's query) inside this component and displaying in > additional fields on this component. > > I just wanted to chek whether this is the right solution? I would design this customer display as a TFrame with one additional pubilc property that takes the customer's primary key as value. The property would have a setter method that would retrieve the customer data from the database when the primary key is changed. The frame would contain whatever database access components it needs to get the data. The form hosting the frame instance (you would have different forms using this frame if I understand you correctly) would assign the foreign key from its dataset to the frame's key property in a suitable event of its dataset, perhaps AfterScroll. This way the frame itself is independent of the form that uses it, and different instances of the frame would also be independent of each other. You could design the frame with data-aware controls as usual. The downside is that each frame uses a separate query or dataset, but they can all share the same database connection contained in some data module. -- Peter Below (TeamB) Don't be a vampire (http://slash7.com/pages/vampires), use the newsgroup archives : http://codenewsfast.com http://groups.google.com
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Peter
5/8/2012 10:06:47 AM
This may work but data binding remains in need for some improvement - e.g. one is required to call the Frame.Id assigment from the FK_CUSTOMERChanged event of the frame's host form (or datamodule) and one is required to assign FK_CUSTOMER field to frame as well - so that Frame can change the value of FK_CUSTOMER (it is not bad idea to display the customer data along the buttons and other components that let's to search and select another customer). That leads to the idea about using TFieldDataLink as TCustomerFrame variable as it would be used it TCustomerFrame would be made as DB aware component. Apparently - The lifecycles of Frame and Component are different and TFieldDataLink perhaps is not appropriate in both cases. Is it good practice to use TFieldDataLink in frames? Edited by: Tom Rhodes on May 8, 2012 12:34 PM
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Tom
5/8/2012 7:35:16 PM
Tom Rhodes wrote: > This may work but data binding remains in need for some improvement - > e.g. one is required to call the Frame.Id assigment from the > FK_CUSTOMERChanged event of the frame's host form (or datamodule) and > one is required to assign FK_CUSTOMER field to frame as well - so > that Frame can change the value of FK_CUSTOMER (it is not bad idea to > display the customer data along the buttons and other components that > let's to search and select another customer). > > That leads to the idea about using TFieldDataLink as TCustomerFrame > variable as it would be used it TCustomerFrame would be made as DB > aware component. Apparently - The lifecycles of Frame and Component > are different and TFieldDataLink perhaps is not appropriate in both > cases. Is it good practice to use TFieldDataLink in frames? Never tried that so cannot comment on it. My solution would be to add a published event property to the frame class that the host form could add a handler for. The frame would fire the event when the user changes the customer displayed in the frame, e.g. by searching or by adding a new customer. The event handler on the host form would then take care of setting the new customer's key as foreign key in its dataset. This way reduces the coupling between frame and host form, the frame needs to know absolutely nothing about the host form to work, and that is what you aim for if you build reusable modules. -- Peter Below (TeamB) Don't be a vampire (http://slash7.com/pages/vampires), use the newsgroup archives : http://codenewsfast.com http://groups.google.com
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Peter
5/9/2012 6:19:40 PM
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