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Problem with Defining Relationsships Between Datatables

Hi experts!
i get error Exception Details: System.ArgumentNullException: 'column' argument cannot be null. Parameter name: column

when i run this code. I have checked both datasets with a repeater and they work fine. What am I doing wrong?

Sub Page_Load(Source as Object, E as EventArgs)

dim ds as dataset
dim da as sqldataadapter
dim prow as datarow
dim crow as datarow
ds = new dataset
   Dim objConn As SqlConnection = New SqlConnection(ConfigurationSettings.AppSettings("ConnectionString"))
da = new Sqldataadapter ("select * from mfg", objConn)
objConn.open()
da.fill(ds, "mfg")
da.selectCommand = new SqlCommand("select distinct category  from products where cdescription like '%kitchen_Sink%' ", objConn)
da.fill(ds, "Products")
objConn.close

ds.relations.add("mfg category", _
ds.tables( "Mfg").columns("mfg"),ds.tables("Products").columns("mfg"))

for each prow in ds.tables("mfg").rows
lbl.text &="<h3>" & prow ("mfg") & "<h3>"
for each crow in prow.getchildrows("mfg category")
lbl.text &="<LI>" & crow("products")

next
next

End Sub
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dplsr
Asked:
dplsr
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1 Solution
 
ptakjaCommented:
In order to add a relation to a dataset, you have to define primary keys for each table within the dataset.

You can do that like this:

        Dim key(1) As DataColumn               'Create array of DataColumn objects
        key(0) = Me.MyDataSet.Tables(0).Columns(0)     ' Put the primary key columns into the array
        Me.MyDataSet.Tables(0).PrimaryKey = key          ' Pass the array into the PrimaryKey property of the table

Also, this may not matter, but in your code above you fill the dataset with a table called "mfg" but then reference it using "Mfg".
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grayeCommented:
Well the 2nd DataTable has only one column, called "Category"...  I can't tell the column names of the 1st DataTable.  Typically you would do a "join" operation on a table with just one column.... so something isn't quiet right there.

So, that DataSet.Relations.Add() method is expecting two *COLUMNS*, so I'd expect it to look like this:

ds.relations.add("mfg category", ds.tables("Mfg").columns("SOME_VALID_COLUMN"), ds.tables("Products").columns("Category"))
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grayeCommented:
...er.... that was suppose to read "Typically you would NOT do a join..."
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ptakjaCommented:
Good catch Graye...

Here's the problem:

da.selectCommand = new SqlCommand("select distinct category  from products where cdescription like '%kitchen_Sink%' ", objConn)
da.fill(ds, "Products")
objConn.close

As Graye said, the Products table only has one column in it called "category".

ds.relations.add("mfg category", ds.tables( "Mfg").columns("mfg"), ds.tables("Products").columns("mfg"))

Your relation has 2 columns in it, however the "mfg" column doesn't exist in the Products table becasue of the Select statement above. At a minimum, you would need to add that column to the SELECT query and you should be OK.




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dplsrAuthor Commented:
Hi all! sorry I was out for the norning! Thanks ptakja! You fixed it, thanks!

da.selectCommand = new SqlCommand("select distinct category,mfg  from CMRC_products where cdescription like '%kitchen_Sink%' ", objConn)
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