SQL logical check in database - VB.net

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Hello Guys,

Am trying to access the MSI database, I can insert, delete etc. in the database.
My issue is how to check for existing entry in the database and Insert if not exists.

I get error in my code below.

installer = CreateObject("WindowsInstaller.Installer")
database = installer.OpenDatabase(Path, 1) 'database will be opened for editing.

SQLquery = "IF NOT EXISTS(SELECT * FROM database WHERE `Feature` = 'Complete') INSERT INTO Feature (`Feature`, `Feature_Parent`, `Title`, `Description`, `Display`, `Level`, `Directory_`, `Attributes`) VALUES ('Complete', '', 'Complete', '', '2', '1', 'INSTALLDIR', '0' )"

View = database.OpenView(SQLquery) ---------> Error: COMException was Unhandled, OpenView,Sql

Please assist me in solving the error in the code.

Posted 10-Sep-14 1:22am

Mohan Subramani

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Richard Deeming · Answer 1 · 2014-09-10T02:10:00

Solution 1

Looking at the documentation[^], Windows Installer does not support the IF NOT EXISTS(...) clause. You'll need to issue separate SELECT and INSERT commands.

Posted 10-Sep-14 2:10am

Richard Deeming

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Mohan Subramani 10-Sep-14 8:42am

Thanks for your reply,
I have gone through the documentation. I will use SELECT and INSERT commands seperatly.
I have a question here,
Can i get value of the executing SELECT statement in a binary 1 or Zero value.
For e.g
SQLquery = "SELECT * FROM database WHERE `Feature` = 'Complete'"
View = database.OpenView(SQLquery) ---> This statement to give values 1 if YES, 0 is No

So that i can execute my next INSERT command accordingly ?

Richard Deeming 10-Sep-14 8:47am

It doesn't look like it; the SELECT statement can only select existing columns, not computed columns.

I suspect you'll need to Execute the SELECT view, then Fetch the first record. If it returns a record, then the feature exists; if it returns Nothing, then the feature doesn't exist.

Mohan Subramani 11-Sep-14 1:37am

I got the tips from msdn link, to do SELECT in a MSI database.
(Am using below code to SELECT a Feature named Complete)

View = database.OpenView("SELECT `Feature`.`Feature` FROM `Feature` WHERE `Feature`.`Feature`= 'Complete'")
View.Execute()
database.commit()

fetchDB = View.fetch()
MessageBox.Show(fetchDB)

If (fetchDB = "") Then
MessageBox.Show("This Database doesnt contain Feature 'COMPLETE'")
End If

i get error in the line "MessageBox.Show(fetchDB)" -- Am not able to convert _COMobject ot String
How can i convert the fetch data from dtabase to string to Check whether it is Null or not

Error:

Invalid CaseException was handled.
Conversion from type '_ComObject' to type 'String' is not valid.

Please assist

Richard Deeming 11-Sep-14 7:44am

You don't need to convert an object to a string to check whether it contains a value.

Try:

fetchDB = View.fetch()
If fetchDB Is Nothing Then
    MessageBox.Show("This Database doesnt contain Feature 'COMPLETE'")
End If