C# Discussion Boards - CodeProject

28-Jul-10 4:17

I have been trying to solve the problem related with using dataRelation but still couldn't figure it out. I hope somebody can help me with this.

I have two repeaters used one nested another.
part of code is shown below:

void Repeater1_ItemDataBound(object sender, RepeaterItemEventArgs e)
       {
           RepeaterItem item = e.Item;
           if ((item.ItemType == ListItemType.Item) ||
               (item.ItemType == ListItemType.AlternatingItem))
           {

               Repeater2 = (Repeater)e.Item.FindControl("Repeater2");
               DataRowView drv = (DataRowView)item.DataItem;
               Repeater2.DataSource = drv.CreateChildView("categoryItem");
               Repeater2.DataBind();
           }
       }

This categoryItem is from this code:

objDA.Fill(ds);
            DataColumn c1 = ds.Tables["category"].Columns["ID"];
            DataColumn c2 = ds.Tables["Item"].Columns["catID"];
            dRel = new DataRelation("categoryItem", c1, c2);
            ds.Relations.Add(dRel);
            Repeater1.DataSource = ds;
            Repeater1.DataBind();

And the error message is:

 Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

Line 1222:            objDA.Fill(ds);
Line 1223:
Line 1224:            DataColumn c1 = ds.Tables["category"].Columns["ID"];
Line 1225:            DataColumn c2 = ds.Tables["item"].Columns["catID"];
Line 1226:            dRel = new DataRelation("categoryItem", c1, c2);

Well the "ID" of table "category" is the foreign key in "item" table and that foreignKey name in the "item" table is "catID".

Any help will be appreciated..

I really need some help in this.

suchita

freakyit28-Jul-10 4:26

freakyit

28-Jul-10 4:26

Line 1222: objDA.Fill(ds);

may objDA is null or ds ^^

Dhyanga28-Jul-10 4:28

28-Jul-10 4:28

thanks for the reply .

ds is not null. If i show the values of ds in datagrid, all those data is shown with no problem..

Grid1.DataSource = ds;
Grid1.DataBind();

the above code is running well.

error is showing on the line 1224 .. Frown | :(

suchita

freakyit28-Jul-10 4:30

freakyit

28-Jul-10 4:30

than objDA will be null the exception is NullReferenceException that implicit says that one object is null at the run time set breakpoints and check if all vars you use are not null.

bless

Dhyanga28-Jul-10 4:34

28-Jul-10 4:34

thanks for the reply again.
it is showing error in line 1224 but since my ds has all the data , i dont know why the error in this line ?

suchita

Eddy Vluggen28-Jul-10 5:03

Eddy Vluggen

28-Jul-10 5:03

Line 1224 consists of multiple statements:

Line 1224:            DataColumn c1 = ds.Tables["category"].Columns["ID"];

I suggest you cut it up into multiple lines, with a breakpoint on each line.
What does ds.Tables["category"] evaluate to? Does that new object have a column labeled "ID"?

SayamiSuchi wrote:
i dont know why the error in this line ?

One of those statements on that line evaluates to null.

I are Troll Suspicious | :suss:

Eddy Vluggen28-Jul-10 5:13

Eddy Vluggen

28-Jul-10 5:13

You're having trouble debugging?

Start here[^] in order to learn how to inspect those values.

I are Troll Suspicious | :suss:

Dhyanga28-Jul-10 5:38

28-Jul-10 5:38

thank you

suchita

Luc Pattyn28-Jul-10 5:00

28-Jul-10 5:00

objDA is probably null

Hmmm | :|

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

Dhyanga28-Jul-10 5:08

28-Jul-10 5:08

objDA is filling ds. ds is getting value.. isn't that means objDA has value ?? Or is there anyway to check the data inside objDA?

Thanks,
suchita

Luc Pattyn28-Jul-10 5:22

28-Jul-10 5:22

I can't tell what is wrong by seeing only some part of the relevant code.
if you think everything is correct, how come the exception?

now replace

objDA.Fill(ds);
...

try {
    if (objDA==null) MessageBox.Show("Oh dear, objDA seems to be null");
    objDA.Fill(ds);
    ...
} catch(Exception exc) {
    MessageBox.Show("exception: "+exc.ToString());
}

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

Richard Blythe28-Jul-10 5:26

28-Jul-10 5:26

Don't take it personal SayamiSuchi. Luc is not partial to any codeproject member. He gripes at all of us! Big Grin | :-D

The mind is like a parachute. It doesn’t work unless it’s open.

Luc Pattyn28-Jul-10 5:47

28-Jul-10 5:47

You know pretty well an open mind is the numero uno prerequisite when debugging some code...

Smile | :)

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

Dhyanga28-Jul-10 5:27

28-Jul-10 5:27

Thank you for the reply.

my code

DataColumn c1 = ds.Tables["category"].Columns["ID"];

is throwing that error. but since my dataset has values, i dont know how come that error ?

suchita

Richard Blythe28-Jul-10 5:41

28-Jul-10 5:41

When I use a DataAdapter to fill a DataTable, I have to manually set the DataTable's name.
If the same logic applies, You may need to manually set the names of your DataSet tables.

The mind is like a parachute. It doesn’t work unless it’s open.

Dhyanga28-Jul-10 5:44

28-Jul-10 5:44

ok. But since i'm using join of two tables, how i'm gonna give two tables name in there ? Or is it just whatever name I'm giving for the dataset ?

suchita

Richard Blythe28-Jul-10 5:54

28-Jul-10 5:54

What is your SELECT query for your data adapter?

The mind is like a parachute. It doesn’t work unless it’s open.

Dhyanga28-Jul-10 6:22

28-Jul-10 6:22

select i.ID,j.Item,j.catID from category i, item j where i.ID = j.catID

suchita

Luc Pattyn28-Jul-10 5:44

28-Jul-10 5:44

assuming ds is a DataSet, that line would throw a NullRefExc only if ds were null or there were no table called "category"

suggestion: split the line into many, and check what gives

if (ds==null) MessageBox.Show("ds is null");
DataTable dtCat=ds.Tables["category"];
if (dtCat==null) MessageBox.Show("dtCat is null");
DataColumn c1=dtCat.Columns["ID"];
MessageBox.Show("we got a DataColumn!");

Luc Pattyn [Forum Guidelines] [Why QA sucks] [My Articles] Nil Volentibus Arduum

Please use <PRE> tags for code snippets, they preserve indentation, and improve readability.

Richard Blythe28-Jul-10 5:03

28-Jul-10 5:03

System.NullReferenceException is an exception that never lies. You are obviously typing a string in wrong.

To eliminate all possible confusion, try this code:

if (!ds.Tables.Contains("category") || !ds.Tables["category"].Columns.Contains("ID"))
   throw new ArgumentException("The category table or column does not exists!")
//
if (!ds.Tables.Contains("item") || !ds.Tables["item"].Columns.Contains("catID"))
   throw new ArgumentException("The item table or column does not exists!")

DataColumn c1 = ds.Tables["category"].Columns["ID"];Line 
DataColumn c2 = ds.Tables["item"].Columns["catID"];
dRel = new DataRelation("categoryItem", c1, c2);

The mind is like a parachute. It doesn’t work unless it’s open.

Dhyanga28-Jul-10 5:23

28-Jul-10 5:23

Thanks for the reply. yes you were right. it threw the argument exception. the query i used for the dataset ds is:

select i.ID,j.Item,j.catID from category i, item j where i.ID = j.catID

and the dataset is having data . Then why it gave that error ?

suchita

Richard Blythe28-Jul-10 5:30

28-Jul-10 5:30

Which one threw the exception? I agree with Eddy that you need to learn how to perform effecient debugging.

Visual Studio wouldn't be worth two cents to me if it didn't have a good debugger.

The mind is like a parachute. It doesn’t work unless it’s open.

Dhyanga28-Jul-10 5:37