alt text http://img29.imageshack.us/img29/825/simplemodel.jpg
How you can see above, it's a kind of subclass a table in a RDBMS (in this case, my favorite: MySQL) so I handle it with Visual Subclassing a base form for tb_order_base with validating field data, etc.
This way, I'm free of repeating code and some other bothering problems, well, it seems a true OO aproach. But ...
Now I got a Big problem with subclassed form i.e. tb_order_service with a master/detail approach, when I post the tb_order_base dataset, instead of Delphi first post it and get the PK ID from RDBMS and then post the TB_ORDER_PRODUCT with id filled, it does the opposed, posting the detail tb_order_product dataset first then master tb_order_base, so I get a big foreing key constraint error.
Does anyone has any idea to how to by-pass this amazing problem?
I have asked it before, but with few details in The Master/Detail Behavior
One thing I have done in such a condition was to break away from doing DBMS direct calls, and to instead use a memory dataset (or client dataset) for the form. When the user presses the save button, I would validate my edits and return any errors. If no errors then I would begin a database transaction, commit the master record (and then read the master record key back if its an insert), then run thru each table commiting the child records, followed by a commit of the transaction (or rollback if there were any problems saving child data).
I also stay away from using data-aware components. They work great for simple utility type programs, but when you start creating a complex system using them you will find little gotchas along the way that are easily solved by using a standard edit and a function to push/pull data to/from the database. The only exception I generally make would be for grids, but I only use the grid for selection...the actual editing is done using non data-aware components.
Related
How can I get from a TClientDataset the changes?
I have a TClientDataset named GetDataset and I have a grid. I want the changes in a new TClientDataset named ChangeDataset.
How can I do this?
If you have a source ClientDataSet CDS1, you should be able to copy the changed records to a second ClientDataSet CDS2 by doing
if CDS1.ChangeCount > 0 then
CDS2.Data := CDS1.Delta;
As you'll see if you try that, it gives you a "before" record and one with the change(s). That may not necessarily be what you want - frankly you'd do best to read the Whipple article posted in a comment and in the OLH to get the exact result you might be wanting to achieve. The point is, all the information you need is in the source CDS until you flush it away (by calling ApplyUpdates() - after that, if it succeeds, the change log is empty).
If you look at the rows in CDS2, it's not immediately obvious how you tell whether a particular field contains a changed value and how you distinguish one that does from one which is just empty. Istr there was a very good post quite a long time ago in one of the Borland NTTP newsgroups by their Mark Edington, I think, explaining how to do this. Basically, it's a question of evaluating VarIsClear on the field's NewValue property:
if VarIsClear(CDS2.Fields[i].NewValue) then
// means Fields[i] does not have a changed value
Incidentally, since you can save the state of a CDS to XML, you can use XML manipulations, e.g. with a DOM parser such is the Windows built-in one (see MSXML.Pas) to do easily many things which are troublesome to do using the TDataSet paradigm.
I need to write a form for creating a new entity and with it, up to 3 relations (which are new entities).
I can either have it dynamically attach/delete them dynamically (which could be useful) or have all 3 always be related to the entity, and for them to have an 'active' boolean on them, which would be just as appropriate.
At what point should I be doing this? I need them rendered as checkboxes on the form.
So far I've tried attaching them to the entity prior to passing it to the form, but choice fields can't be passed unmapped entities, so that's no good.
I've also tinkered with a DataTransformer for this, although then, as far as I can see, I would have to create new entities in the DataTransformer, which seems wrong, and I can't get to work anyway- I don't have access to the entity within it and even hacking around that, the relationship fails to bind properly (Doctrine tries to save the relationships first).
In Symfony1 terms, I could just embed a couple of forms for each additional relation I needed, using new objects, and it'd just work, so surely there's still a relatively easy way around this?
A friend also recommended looking into the ResizeFormEventListener, but this, as far as I understand, is for 'resizing' a form based on the returned data, whilst I never want the form to change, I want 3 checkboxes always.
What's the best way to approach this problem?
I'm not sure on exact details without playing with it - but based on how i've done similar things, i'd be looking to use a 'collectiontype' and then adding the three department types into that.
I am making a app in Delphi 6 + MySQL database using standard data-aware components and dbExpress. The app allows a users to view records in a grid and edit data (insert and/or delete records) client side. These data edits are then only written to database on clicking the submit button. All of this works fine and has the following setup:
Controls:
1. DBGrid1 linked to a DataSource1 to display data visually.
2. DataSource1 is linked to ClientDataSet1 to offer data for DBGrid to display.
3. ClientDataSet1 is linked to DataSetProvider1 to provide client-side data for editing.
4. DataSetProvider1 is linked SQLDataSet1 which selects records from a single DB table.
5. SQLDataSet1 is linked to SQLConnection to provide connection to MySQL database.
Actions:
1. User inserts a record: I use ClientDataSet1.InsertRecord;
2. User deletes a record: I use ClientDataSet.Delete;
3. User submits data: I use ClientDataSet1.ApplyUpdates(-1);
This all works great in terms of handling data & posting data (with the inclusions of a small hack on DataSetProvider1BeforeUpdateRecord to delete records).
NOW FOR MY PROBLEM:
When the user first loads the form, the DBGrid1 displays all original records, removes all deleted records. But when the user inserts a new record in ClientDataSet1, a blank record is displayed in DBGrid1. The actual data is not lost or set as NULLS as when you ClientDataSet1.ApplyUpdates, this record is correctly written to the DB.
I know TClientDataSet has a data property for original data and a Delta property for edited data. Can these two properties with data by displayed in a single DBGrid at one time & still allowing the user to edit the data?
I have looked at 30+ resources and demo apps & all avoid this issue. Can this be done?
Ok...this question has been viewed a fair amount without much feedback. I did some research by downloading many tutorials, demo apps & read multiple articles/help info discussing the use of these controls.
The net result:
These controls are a bit buggy in general.
In specific reference to my question, it is safe to say the controls cannot do what I describe as a standard.
This is based on the 30+ demo apps, articles and tutorials I reviewed that either don't describe displaying both the original data with Delta data in a single data grid. Sure you could hack this outcome (which is what I did) using a Listbox or StringGrid, but that also indicates the control cannot or not usable at providing this functionality (on the slim chance it might).
This functionality is an obvious oversight in my opinion as a user wants to see the potential outcome of their actions, conveniently in a single data grid AND a developer wants to provide that in a simple & pain free way i.e. using a datagrid to display data!
Question Answered [if you can prove differently with a demo app that I want to review, I will remove this].
If you created a demo app and couldn't get it to work, up vote my answer. Thanks
The TDBGrid control provided with Delphi does not have the built-in functionality to display both the old and new values for fields. You are welcome, of course, to inherit from the Grid or create your own and add the functionality, or buy a third party component that accomplishes what you want. You are not limited to the standard controls, though they do provide the most commonly required functions.
You can also accomplish what you want by using calculated fields. For example, if you have a String field Name, add a new calculated String field to the dataset called OldName, with the same length as Name.
Then in your OnCalcFields event for the dataset, simply enter code like the following:
if DataSet.State = dsEdit then
begin
DataSet.FieldByName('OldName').Value := DataSet.FieldByName('Name').OldValue;
end
else
begin
DataSet.FieldByName('OldName').Value := Null;
end;
TClientDataset will handle itself the correct record status. Changes are logged, but unless you ask it explicity to show some other status (see StatusFilter property), it will show the actual state of a record.
It is possible InsertRecord bypasses some notification mechanism, so the field display is not updated. What if you perform simpy an Insert and the set field values?
I'm coming from the delphi world and I want to make a master/detail interface, like Order and Products.
I already made actions to display the data using fields and a jqGrid. What I want know is how make possible to add lines, edit or remove them, but, just make the changes in db when the user confirm the changes in the master.
On delphi I would use a TClientDataSet with all the in memory changes and just after the confirmation would execute them inside a transaction like:
BEGIN
Master.Post
FOREACH Line IN Lines Line.Post
COMMIT
So in resume, I don't know how keep in memory the array of lines in the grid and how send them back to server to commit.
Any help will be appreciated. Thanks in Advance.
You'll need to keep track of the changes client side, perhaps using some hidden fields and/or form fields in your grid. When a line is deleted (that previously existed in the db), you'll need to add it's id to a field containing lines to delete. Lines that are added need to have associated form fields containing their data. When the master is committed you roll the whole set of fields up into a POST and send that back to the server.
Using LINQ to SQL, you'd create a data context, get the master object, then delete the related objects (from the hidden field of ids) that are so marked and create/add new related objects that didn't exist before taking the values from the appropriate form fields. Then you'd do a SubmitChanges and all of the statements would be executed within a single transaction.
Ok, so this is an alternative to this question.
I'm trying to produce an MVC application using LinqToSql that allows for bulk editing of data on a single page.
Imagine a simple table Item with ItemId, ItemName, ItemPrice as fields.
There are many examples out there of extrmely simple MVC applications that show you a list of these items with an edit button next to each and an add button at the bottom.
From a UI perspective I find this very time consuming when a lot of data needs entering / updating.
I'm after a single page containing the items names and prices in textboxes that can all be edited in one go and then a single "Save" button pressed to update the data.
I've seen a number of examples that perform various stages of this but have yet to find one that implements the full solution. In particular the interaction with Linq.
I have a number of methods I've tried which all work, however, my gut feeling tells me my methods "smell" and therefore I'd like to see some examples of how other people have attempted this.
So, put simply, my question is can anyone provide some links to some examples please?
I have written about how to do this with MvcContrib's FluentHtml. Steve Sanderson has written about how to do it without FluentHtml. Both of our articles have a sample solution you can download and look at.
As far as LinqToSql, I would consider any interaction between bulk editing mechanism (controller and view) and LinqToSql to be a smell. That is to say, as far as possible your UI should be ignorant of your persistence mechanism.
What I would probably do to get around this is use jQuery to call a jsonResult when you switch rows. This jsonResult would call the code in the model to save the ItemId, ItemName, ItemPrice for only the row you are switching off of. More on general jsonResult w/ jQuery usage here : http://www.dev102.com/2008/08/19/jquery-and-the-aspnet-mvc-framework/
The other thing you could do is do model binding to a list of Items, iterating thru the list saving each item -- Phil Haack has an example of list binding here: http://haacked.com/archive/2008/10/23/model-binding-to-a-list.aspx With either method you'll want to do something to signify the row has changed so you're not updating every field if you're just changing a handful of rows.
What is your goal exactly, are you trying to commit a series of information all at once? Or do you simply not want your page to postback every time you change something. In either case jQuery is your best bet. If you want to do everything in one pass it is going to get complex unless you use a jQuery control that will do this for you. There are some great ones out there such as the Flexigrid.