adding a primary key to a dataset/datatable

[Bernie Yaeger]

I have a need to add a primary key to a dataset/datatable. How can this be
done using a standard oledb data provider?

Tx for any help.

 

[Arsalan]

OleDataAdapter should have primary key in its select command/statement,
for e.g Select Employee_ID from employees

Then use fill command to fill the dataset

OleDataAdapter.Fill(Dataset)
thats it, you'll have primary key in ur dataset

 

[Bernie Yaeger]

Hi Arsalan.

I am working with vfp free tables - there are no primary keys in the
original tables and they can't be added to the backend (because they are not
mine and adding a column would screw them up).

Bernie

 

[Arsalan]

If the table structure doesn't contain primary key then its impossible to
add it to the dataset.
How about making a column alias from two or more columns [like composite
primary key] that would make it possible to select records from the table,
it all depends on what kind of column u have in ur database table

 

[Brian Swanson]

I assume you are asking to add a primary key just for processing while
the dataset/datatable is in memory and aren't trying to write it back
out anywhere.

You can add a primary key by using the PrimaryKey property on a
DataTable

You can use the following code as an example:

Dim lds as DataSet = GetSomeDataSet()

For Each ldt As DataTable In lds.Tables
ldt.PrimaryKey = New DataColumn() {ldt.Columns("ColumnName")}
Next

-------

A couple things to note here. This iterates through each datatable
that's returned in the dataset, you can run the line inside the
for..each by itself if you only want to create a PrimaryKey for just one
table.

Also, if you want to make a multi-column primary key then the line
inside the for..each would look something like this:

ldt.PrimaryKey = New DataColumn() _
{ldt.Columns("ColumnName1"), ldt.Columns("ColumnName2")}

Hopefully this makes sense...

Brian Swanson

 

[Brian Swanson]

One other note...

When adding the primary key in this way the system doesn't automatically
set the column you assign to the primary key as unique. You have to do
this as well by using:

ldt.Columns("ColumnName").Unique = True

 

[Bernie Yaeger]

Hi Brian,

I looked at a couple of books I have on my shelf and figured this out, but
thank you.

Unfortunately, I do want to write it back to the backend, and, as luck would
have it, this does me absolutely no good! (as your caveat suggested). But
thanks for responding.

Bernie

 

[Cor Ligthert]

Bernie,

What is it you want to achieve setting a primary key in the tables of your
foxpro database.
Or use as Brian wrote use it internally by instance to set a relation.

For me it is as well not clear which of the two it is (because I have readed
your previous questions).

Cor

 

[Bernie Yaeger]

Hi Cor,

I tried it, and it doesn't achieve my goal. I was hoping that it would
somehow enable me to update the back end more effectively, but it did not.

Bernie

 

[Cor Ligthert]

Bernie,

Your goal is not clear in my opinion.

Do you want to set the keys in the database
Or
Do you want to set the primary keys in the dataset.

Where I assume setting the primary keys in the database using the SQL Alter
command and the

http://msdn.microsoft.com/library/d.../en-us/fox7help/html/lngalter_table___sql.asp

the SQLcommaned.executenonquery to process that.



Cor

 

[Bernie Yaeger]

Hi Cor,

The problem with that is, I am not allowed to alter the tables - they belong
to a third party. I am simply hooking into them.

I've come to the conclusion that I will only be able to do this by using the
foxpro environment itself, but I probably won't have to - it appears my
client will be happy with 'view access' only, so I can hook in, gather the
data I need, and display it.

Tx for your help.

Bernie