I need to create an Aggregate Field in a TClientDataSet, but as said in the docs:
Choose OK. The newly defined aggregate
field is automatically added to the
client dataset and its Aggregates
property is automatically updated to
include the appropriate aggregate
specification.
When I add a new aggregate field, the aggregate specification isn't added to the TClientDataSet's Aggregates, therefore I can't use its OnUpdateMethod.
I also tried handling the OnChange event of my new Aggregate Field, but it isn't fired at all.
Am I doing something wrong? I just want to have an aggregated field and fire an event everything it's value change.
Is this broken on delphi? Because what is in the documentation doesn't reflect the actual behavior.
edit:
#Michal Sznajder
I'm using Delphi 2007
I think you may be getting confused between TAggregate and TAggregateField objects, and the Delphi documentation probably isn't helping.
AFAICT, TAggregateField objects are automatically 'recalculated' and can be bound to data-aware controls like TDBText, but don't have any OnUpdate event.
"TAggregate" objects, on the other hand, do have an OnUpdate event, but can't be bound to data-aware controls.
This may be enlightening: http://dn.codegear.com/article/29272
Which version of Delphi ? I just tried clean D7 application and TAggregateField was added.
Related
This is a simple question.
Start a multidevice App, place a TDateEdit and DBTable with a field containing TdateTime data. Then use LiveBinding designer link the data source field to TDateEdit.DateTime property. However, this link is unidirectional , The control DateEdit can accept the data from the Datasource, but cannot update the changes to the datasource. How to change the link to bidreiction???
There may be some things that are not clearly understood.
Normally a LiveBindings link will be bidirectional - so if you setup two TDateEdits and bind them together changing one should change the other, irrespective of which one you change.
It seems that what you are hoping is that changing the TField will update the data in the database table.
That's not typically how the Data Access components in Delphi work.
The TField is part of a TDataSet. The TDataSet has a Post method to write changes to the underlying data store, if that's supported.
The Data Access components are extremely powerrful and can cope with lots of different scenarios, and allow you to extended capabilities throguh exposed events as well as subclassing the components.
If you want to update your underlying data store you need to have a writeable TDataSet and you need to call Post on it to write.
I suggest you start off with some of the videos in Enbarcadero's YouTube channel about how to use the data acecss components. It's not difficult to do but beyond the scope of an answer here.
If you use the LiveBindings Wizard to hook the DateEdit with a field, it will hook it up bi-diretionally to a "virtual" SelectedDateTime property of the DateEdit. That property doesn't really exist in the TDateEdit but is used by the LiveBindings to map the separate Date and Time properties of the DateEdit.
I want to load the content of of dbctrlgrid at runtime (from database). So I encountered several challenges:
How to detect if the dbctrlgrid is empty and/or how to clear it.
How to put Tlabel and Tdbtext on the panel. The main problem seems to be to find the right parent. dbctrlgrid doesn't work. There is an object called Tdbctrlpanel which should work, but I don't know how to access it. I could not find it in properties or methods of Tdbctrlgrid.
Any code snipplet is welcome
To answer 1)
You don't query the TDBCtrlGrid, you query the underlying dataset; if it .IsEmpty the grid is empty.
When people start using data aware (grid) components they have the tendency to see that as the 'data container' that you can query and modify, but that is not the case. See it as a view on your underlying data with some built-in editors that modify that data. Then the 'same rules' apply to you as to these editors: update the underlying dataset.
To add controls to a TDBCtrlGrid you have to set the controls parent to the Panel property of the TDBCtrlGrid. The problem is that this property is protected. There are several ways to overcome this limitation. One is shown at Delphi About: Accessing protected members of a component
This is a common technique known to Delphi programmers as the 'protected hack'.
Everyone probably knows what I mean, but to clarify the control would need to:
Fire an event when user edits the text. The event would provide a SuggestionList: TStrings which you could fill with matches/suggestions.
if the SuggestionList is not empty a drop down should appear.
Unlike combo, the control should not attempt to automatically select/auto complete or otherwise affect the editing.
So, is there a Delphi edit/combo control that works like that ?
Use the autocompletion feature built in to all Windows edit controls.
First, fill your TStrings object however you want. Then use GetOleStrings to create a TStringsAdapter to wrap it. (The adapter does not claim ownership of the TStrings object, so you must make sure you don't destroy it while the adapter is still live.) The adapter gives you an IStrings interface, which you'll need because the autocompletion feature requires an IEnumString interface to provide the completion matches. Call _NewEnum for that.
Next, call CoCreateInstance to create an IAutoComplete object. Call its Init method to associate it with the window handle of your edit control. If you're using a combo box, then send it a cbem_GetEditControl message to find the underlying edit window.
You can stop at that point and autocompletion should work automatically. You can disable autocompletion if you want, or you can set any number of autocompletion options.
You say you don't want autocompletion, but in the OS terminology, I think what you really don't want is called auto append, where the remainder of the string is entered into the edit box automatically as the user types, but selected so that further typing will overwrite it, and the user needs to delete the excess text if the desired value is shorter than one of the matches.
There is also auto suggest, which displays a drop-down list of suggestions.
You can enable either or both options. You don't need to filter the list of suggestions yourself; the autocomplete object filters the IEnumString list by itself.
You can use standard TComboBox and faststrings library (for stringMatches() function).
procedure TForm1.cbChange(Sender: TObject);
var
s:Integer;
tmpstr:string;
begin
//suggestions: tstringlist
cb.AutoComplete:=false;
tmpstr:=cb.Text;
cb.Items.Clear;
for s:=0 to suggestions.Count - 1 do
if StringMatches(suggestions[s],cb.Text+'*') then
cb.Items.Add(suggestions[s]);
cb.DroppedDown:=(cb.Items.Count<>0) and (Length(cb.Text)<>0);
cb.Text:=tmpstr;
cb.SelStart:=Length(cb.Text)
end;
If you just want to show a file or url list:
SHAutoComplete(GetWindow(eb_MyComboBox->Handle, GW_CHILD), SHACF_AUTOSUGGEST_FORCE_ON | SHACF_FILESYS_DIRS);
I first implemented this feature like Rob described it in his answer. Later I saw that TComboBoxEx has the property AutoCompleteOptions where I set acoAutoSuggest to True and acoAutoAppend to False. The ComboBox now filters its item list when doing some entry and shows the matching items.
I'm using RAD Studio 10 Seattle and XE2 but don't know if this feature is available in older versions.
To the last bit of your question: "So, is there a Delphi edit/combo control that works like that ?":
A bit late to the party but yes, I have written a free and open source component that implements the Google Place Autocomplete and Google Place Details API's:
It does inherit from the standard TComboBox but you can modify the code to work with any TEdit
https://carbonsoft.co.za/components/
or
https://github.com/RynoCoetzee/TRCGPlaceAutoCompleteCombo
I have the following DBX structure in my software:
TSQLDataSet -> TDataSetProvider -> TClientDataSet
One of the fields from my TClientDataSet has the property Required set to false, because this field auto increments based on triggers and generators on the database (Firebird).
However, after configuring both TSQLDataSet and TClientDataSet with this field not being required, I'm getting really weird results when I try to read this field from my TClientDataSet. I suspect that I might need to do something extra to force my TClientDataSet to acquire the value of this field in this condition.
What am I missing here?
Thanks in advance.
EDIT
The help file for the Required property says something about this, but I couldn't quite understand what it want me to do.
Description
Specifies whether a nonblank value for a field is
required.
Use Required to find out if a field requires a value or if the field
can be blank.
If a field is created with the Fields editor, this property is set
based on the underlying table. Applications that set Required to true
for fields that must have values (for example, a password or part
number), but for which the underlying table does not require the
field, must write an OnValidate event handler to enforce the property.
When the Required property reflects a property of the underlying
database table, trying to post apply a null value causes an exception
to be raised. Applications that set the Required property to true when
the underlying table does not require the field, should raise an
EDatabaseError exception on null values in the OnValidate event
handler in order to achieve the same result.
EDIT 2
Forgot to mention: between the TDataSetProvider and the TClientDataSet, there is a DataSnap layer (the TClientDataSet connection is made with a DataSnap driver).
EDIT 3
I created a small test case with this DataSnap setup and it worked perfectly. The project is legacy, messy and I guess that either I have an obscure option configured somewhere that is biting me or I have stumbled in a DataSnap bug.
Haole, have you tried TClientDataset.RefreshRecord after inserting? Or even TClientDataset.Refresh?
Having generators, you can even get the generator in advance (before calling ApplyUpdates) in a query like select gen_id(generator,1) from RDB$Database (it's from memory, don't have Firebird here to test) and fill the PK field in advance.
EDIT: seems this is a heisenbug. I would try to remove the components and reconfigure them again from scratch (which means: after you remove, save and close Delphi).
Or even better, create an empty project with just that needed query configuration and try to view that data in a TDBGrid. If this problem still happens, maybe your FB installation have some component corrupted (or even Delphi installation)
Seems that the problem was an outdated field being read as an INTEGER and it was a SMALLINT in the database.
This problem was hard to debug and this question was misleading. Thanks for everyone that helped me debug this.
When I use a TClientDataSet which is connected to a TxxxQuery component, I can add TFields to both components at design time. I recognized, when I don't specify the TFields in the TxxxQuery component, they are retrieved when the query is executed at runtime.
My questions is: Is there a performance difference when I add the TFields at design time to the TxxxQuery component?
When you add the fields at design time you get the strongly typed QueryName_FieldName fields you can use directly from code, skipping the name-based QueryName["FieldName"] lookup required if you don't have them.
From a performance stand-point the difference is most likely insignificant; From a language perspective having the fields added at design time provides better type safety, but only if you access the fields from code, and only if you use the QueryName_FieldName.Value syntax, not the named-based QueryName["FieldName"] syntax. If you use data-bound controls there's no difference.
I personally only add fields to TClientDataSet at design time when I need to use the client dataset without binding it to an other data source (ie: use it as a temporary table for reporting).