MSDN Examples flawed

  • Thread starter Thread starter Stamen Gortchev
  • Start date Start date
S

Stamen Gortchev

Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how they look
like:

========================
On Page_Load
if !IsPostBack: BindGrid()

On_Edit
Set datagrid's EditItem to clicked item
BindGrid

void BindGrid()
Fill DataSet through dataadapter
DataGrid.DataBind()
========================

Imagine a simple table "Names" with two columns: NameID and Name

Your SQL Select Statement reads "SELECT NameID, Name FROM Names ORDER BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I thought of a
logical solution which however does not work. In case a discussion occur, I
will write about it.

All best

Stamen
 
Stamen,

Typically when doing an operation like this you wouldn't rebind the grid
before the edit operation.

So, in the page load sub use:

If Not IsPostBack Then
'---Bind your grid here
End If

(Make certain that viewstate is turned on for the grid. This way you don't
have to rebind the grid.)

Then rebind the grid after you edit the data.

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche
 
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen


S. Justin Gengo said:
Stamen,

Typically when doing an operation like this you wouldn't rebind the grid
before the edit operation.

So, in the page load sub use:

If Not IsPostBack Then
'---Bind your grid here
End If

(Make certain that viewstate is turned on for the grid. This way you don't
have to rebind the grid.)

Then rebind the grid after you edit the data.

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how they look
like:

========================
On Page_Load
if !IsPostBack: BindGrid()

On_Edit
Set datagrid's EditItem to clicked item
BindGrid

void BindGrid()
Fill DataSet through dataadapter
DataGrid.DataBind()
========================

Imagine a simple table "Names" with two columns: NameID and Name

Your SQL Select Statement reads "SELECT NameID, Name FROM Names ORDER BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I thought
Click to expand...
of
a
logical solution which however does not work. In case a discussion
Click to expand...
occur,
I
will write about it.

All best

Stamen
Click to expand...
Click to expand...
 
Stamen Gortchev said:
Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how they look
like:
Click to expand...

Could you please post a reference to an MSDN article which says you should
reload the data from the database before the edit?
 
Stamen,

As long as your entries have a primary key I don't see how they could be
compromised. Of course any well designed database uses a primary key to make
certain that a row is unique.

Are the Id's that you are referring to not primary keys?

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen


S. Justin Gengo said:
Stamen,

Typically when doing an operation like this you wouldn't rebind the grid
before the edit operation.

So, in the page load sub use:

If Not IsPostBack Then
'---Bind your grid here
End If

(Make certain that viewstate is turned on for the grid. This way you don't
have to rebind the grid.)

Then rebind the grid after you edit the data.

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how they look
like:

========================
On Page_Load
if !IsPostBack: BindGrid()

On_Edit
Set datagrid's EditItem to clicked item
BindGrid

void BindGrid()
Fill DataSet through dataadapter
DataGrid.DataBind()
========================

Imagine a simple table "Names" with two columns: NameID and Name

Your SQL Select Statement reads "SELECT NameID, Name FROM Names ORDER BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I
Click to expand...
Click to expand...
thought
of occur,
Click to expand...
Click to expand...
 
John,

an example of Datagrid using can be found at:
http://msdn.microsoft.com/library/en-us/cpguide/html/cpconupdatingdatainsqldatabase.asp?frame=true

Forget the Update event, concentrate on the Edit -it illustrates the point
nicely.

What they do is the following:
They get the row number (for example 2) which should be edited from the
datagrid's viewstate and set this row in the datagrid to be edited (row 2).
then they re-read the data and rebind the grid. If, however, the newly
reloaded data contains another row on that place (2) we get the
inconsistency.

I tried Auto generate columns=true, primary keys and so on... nothing
wirks..

Thanks
Stamen
 
Hi Justin,

the table has two Columns: CountryID and Country - the sorting is done on
Country not on CountryID, which of course is a primary key. The prblem of
this approach is that it expects when refilling the datagrid that all
records will come in the same order, what is quite an optimistic expectation
in the general case.

I tried your proposition of not refilling the dataadapter - it does not work
at all, as now data gets shown on the repost.

I had tried another approach:

On_Edit_Event
set editIndex=clickedIndex
Exit

hoping that the grid gets reloaded from the ViewState. Unfortunately this
does not work for some reason: The first time i click [Edit], nothing
happens. The second time I click - the record enters edit-state wehich I
have clicked the first time - so there is something like a "one click lag".
Therefore i think that the event comes up too late - when the grid has
already been initialized or somethink like that..:-(

That's it! The most rigorous approach seems to be like this:

In the edit_event, read the id of the data reord (CountryID). Refill the
Grid. Find the row containing the data record with the found ID. Set this
row in Edit mode. But it beats the purpose of ViewState and all..

Sorry for the long message

Cheers

Stamen



S. Justin Gengo said:
Stamen,

As long as your entries have a primary key I don't see how they could be
compromised. Of course any well designed database uses a primary key to make
certain that a row is unique.

Are the Id's that you are referring to not primary keys?

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen
Click to expand...
ORDER
BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I
Click to expand...
thought
of
a
logical solution which however does not work. In case a discussion occur,
I
will write about it.

All best

Stamen
Click to expand...
Click to expand...
Click to expand...
 
Stamen,

In the example I emailed to you I forgot to tell you to also remove the
databind. Of course if you databind to an empty dataset your grid will be
blank.

You should be making certain that the datagrid itself has it's viewstate set
to true (as should any object it may be contained in such as a panel and the
page object.

Then your code should simply set that row to be editable:

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
DataGrid1.EditItemIndex = e.Item.ItemIndex;
}

Since the datagrid is now not being repopulated from the database it will
only contain the original data and thus no problem...

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen


S. Justin Gengo said:
Stamen,

Typically when doing an operation like this you wouldn't rebind the grid
before the edit operation.

So, in the page load sub use:

If Not IsPostBack Then
'---Bind your grid here
End If

(Make certain that viewstate is turned on for the grid. This way you don't
have to rebind the grid.)

Then rebind the grid after you edit the data.

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how they look
like:

========================
On Page_Load
if !IsPostBack: BindGrid()

On_Edit
Set datagrid's EditItem to clicked item
BindGrid

void BindGrid()
Fill DataSet through dataadapter
DataGrid.DataBind()
========================

Imagine a simple table "Names" with two columns: NameID and Name

Your SQL Select Statement reads "SELECT NameID, Name FROM Names ORDER BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I
Click to expand...
Click to expand...
thought
of occur,
Click to expand...
Click to expand...
 
Stamen,

In the example I emailed to you I forgot to tell you to also remove the
databind. Of course if you databind to an empty dataset your grid will be
blank.

You should be making certain that the datagrid itself has it's viewstate set
to true (as should any object it may be contained in such as a panel and the
page object. The datagrid should certainly re-populate itself from
viewstate. If it doesn't then something else is wrong with your code.

Then your code should simply set that row to be editable:

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
DataGrid1.EditItemIndex = e.Item.ItemIndex;
}

Since the datagrid is now not being repopulated from the database it will
only contain the original data and thus no problem...

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hi Justin,

the table has two Columns: CountryID and Country - the sorting is done on
Country not on CountryID, which of course is a primary key. The prblem of
this approach is that it expects when refilling the datagrid that all
records will come in the same order, what is quite an optimistic expectation
in the general case.

I tried your proposition of not refilling the dataadapter - it does not work
at all, as now data gets shown on the repost.

I had tried another approach:

On_Edit_Event
set editIndex=clickedIndex
Exit

hoping that the grid gets reloaded from the ViewState. Unfortunately this
does not work for some reason: The first time i click [Edit], nothing
happens. The second time I click - the record enters edit-state wehich I
have clicked the first time - so there is something like a "one click lag".
Therefore i think that the event comes up too late - when the grid has
already been initialized or somethink like that..:-(

That's it! The most rigorous approach seems to be like this:

In the edit_event, read the id of the data reord (CountryID). Refill the
Grid. Find the row containing the data record with the found ID. Set this
row in Edit mode. But it beats the purpose of ViewState and all..

Sorry for the long message

Cheers

Stamen



S. Justin Gengo said:
Stamen,

As long as your entries have a primary key I don't see how they could be
compromised. Of course any well designed database uses a primary key to make
certain that a row is unique.

Are the Id's that you are referring to not primary keys?

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen


Stamen,

Typically when doing an operation like this you wouldn't rebind the grid
before the edit operation.

So, in the page load sub use:

If Not IsPostBack Then
'---Bind your grid here
End If

(Make certain that viewstate is turned on for the grid. This way you don't
have to rebind the grid.)

Then rebind the grid after you edit the data.

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Hi all,

I think there is an inherent problem with most examples on the internet
(with MSDN, too!) showing datagrid's databinding. Here is, how
Click to expand...
they
look
like:

========================
On Page_Load
if !IsPostBack: BindGrid()

On_Edit
Set datagrid's EditItem to clicked item
BindGrid

void BindGrid()
Fill DataSet through dataadapter
DataGrid.DataBind()
========================

Imagine a simple table "Names" with two columns: NameID and Name

Your SQL Select Statement reads "SELECT NameID, Name FROM Names
Click to expand...
ORDER
BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE
someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit
button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to
guard
against this problem?

Thank you for taking your time and understanding what I mean. I thought
of
a
logical solution which however does not work. In case a discussion
occur,
I
will write about it.

All best

Stamen
Click to expand...
Click to expand...
Click to expand...
 
Stamen Gortchev said:
Hi Justin,

the table has two Columns: CountryID and Country - the sorting is done on
Country not on CountryID, which of course is a primary key. The prblem of
this approach is that it expects when refilling the datagrid that all
records will come in the same order, what is quite an optimistic expectation
in the general case.

I tried your proposition of not refilling the dataadapter - it does not work
at all, as now data gets shown on the repost.

I had tried another approach:

On_Edit_Event
set editIndex=clickedIndex
Exit
Click to expand...

Try calling DataGrid.DataBind after you set EditItemIndex.
 
Stamen Gortchev said:
John,

an example of Datagrid using can be found at:
Click to expand...
http://msdn.microsoft.com/library/en-us/cpguide/html/cpconupdatingdatainsqldatabase.asp?frame=true

Stamen,

I took a look at that link, you're correct - that's a bug.

I submitted the issue to Microsoft by clicking the "feedback" link at the
bottom of the page. I got a response saying they'll look into correcting it
in future documentation. I was also told that the same pattern is used in
several places in the documentation and in the QuickStarts, and that the
issue will be raised for both.

I've had good response from the Microsoft Documentation and Training people
when I've commented on the MSDN documentation. I've always received a
prompt, courteous and even intelligent response. I haven't seen the results
in the documentation yet, but I'll be checking when the 2.0 documentation
comes out. : -)
 
Justin,

sorry for the late response - I only use newsgroups from work..

I know what you mean and I have tried it. Unfortunately, I still have that
"one-click-delay". All I do is this:
I pul a dataadapter on my Webform, fill dataset and bind it to a datagrid
(all done with my mouse). Then in the page_load event I call
If not ispostback
dataadapter.fill (ds, tablename)
datagrid.databind

And the Edit-event is the way you tell me. And it is still not
working..:-( I do not tamper with the viewstate of neither element as per
default it is always set to true, isn't it? I use VS2003.

If you think I foget something, can you please send me a small example where
it works - I hope it would be interesting for you to try it for yourself and
then ou can perhaps email it to me. I will write you an email in order not
to get thousands of virus mails into my mailbox.

Thanks again

Stamen

S. Justin Gengo said:
Stamen,

In the example I emailed to you I forgot to tell you to also remove the
databind. Of course if you databind to an empty dataset your grid will be
blank.

You should be making certain that the datagrid itself has it's viewstate set
to true (as should any object it may be contained in such as a panel and the
page object.

Then your code should simply set that row to be editable:

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
DataGrid1.EditItemIndex = e.Item.ItemIndex;
}

Since the datagrid is now not being repopulated from the database it will
only contain the original data and thus no problem...

Sincerely,

--
S. Justin Gengo, MCP
Web Developer

Free code library at:
www.aboutfortunate.com

"Out of chaos comes order."
Nietzche


Stamen Gortchev said:
Hallo Justin,

thanks for replying. What you propose however is exactly what I am doing:
The code below is not immune against database changes:

private void Page_Load(object sender, System.EventArgs e)
{
if (!IsPostBack)
{
this.da.Fill(ds1, "Countrys");
this.DataGrid1.DataBind();
}
}

private void DataGrid1_EditCommand(object source,
System.Web.UI.WebControls.DataGridCommandEventArgs e)
{
this.da.Fill(ds1, "Names");
DataGrid1.EditItemIndex = e.Item.ItemIndex;
DataGrid1.DataBind();
}

What do you think about it?

Thanks
Stamen
Click to expand...
ORDER
BY
Name" and you have two records in it:
ID=1, Name = "aaaa"
ID=2, Name = "cccc"

So, the first time you call the page, you get following grid:
1 "aaaa" edit-button
2 "cccc" edit-button

during the time in which you are viewing this html page on your IE someone
inserts another record in the table: "ID=3, Name='bbbb'".
Then you click the edit button of the second row into your grid (2
"cccc") intending to edit the name "cccc". When you klick the edit button,
however, you get following grid:
1 "aaaa" edit-button
3 [bbbb] - updatable!!! Update-button, cancel-button
2 "cccc" edit-button

I am sure, you ghet what the reason is. What is the best solution to guard
against this problem?

Thank you for taking your time and understanding what I mean. I
Click to expand...
thought
of
a
logical solution which however does not work. In case a discussion occur,
I
will write about it.

All best

Stamen
Click to expand...
Click to expand...
Click to expand...
 
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