Problems with Delphi XE2, DataSnap and Lookup Field

1
votes

I have a bit of problem here. I have created a lookupfield in my application server using Delphi XE2 DataSnap technology. On the client side, that field becomes TStringField. Now, the problem is that I loose the lookup functionality on the client side. To top that, I can't change the stringfield on the client side because it is read only (even if I manually turn off the read only property).

I don't want to lookup tables on the client side because I don't want all the data loaded on my client side just to support look up.

I can change the Key field value, but the stringfield lookup text doesnt change unless I apply updates and reload the data.

Users want to see the text change.

What should I do?

2
delphifieldlookupdatasnap
How are you able to write to a lookup field in a normal (non-DataSnap) app? – mjn
non DataSnap is a simple. You create a lookup field and that's all. However, with Datasnap, its a different matter all together (as explained above). – Nirav KAKU

2 Answers

0
votes

Seems you have to review your GUI functionality: lookup fields are really an client side feature. And it needs the lookup source - so to use it on client the lookup table must be loaded. DataSnap guys are very nice here, converting it to an TStringField when transmitting it to the client... I would simply ignore it.

So, if the lookup table is that big, you shouldn't using lookup fields but search UIs - or autocomplete comboboxes which you do queries against the DataSnap Server. Maybe you have to code it manually in the combobox case, I don't know (see if JVCL have something you can use to shortcut the path).

Alternatively, if the lookup table are seldom updated, you can aggresively cache it and have an updating mechanism to detect changes. So you can use the lookup fields the way they were created for.

0
votes

Long time ago i faced that problem and i found a solution that is a bit complex to analyze here but i try to give some guidelines till i have the time to write a detailed blog post. The idea consists of info (concerning lookup fields such as field properties, datasets, providers) packaged by the provider as optionalparams at the server side. At client side a derived TClientDataset can unpack and process these info, create on the fly client datasets that retrieve needed lookup datasets and setup it's lookup fields accordingly. The process is transparent due to the embedded functionality in the derived client dataset class and the only things to remember is to create that info in the provider's OnGetDatasetProperties event and turn false all provider flags in lookup fields.