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Updating a backend

Posted on 2002-05-12
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Last Modified: 2006-11-17
Hi all,

My question is... How do you manipulate backend tables/fields from the linked frontend.

In particular I would like to be able to (from code in the front end when a certain form is opened) add new fields to tables, modify relationships, redefine fields, create and delete fields or tables all from the front end.

Can this be done.  Examples would be most welcome.

Thanking you all in advance...
Mavreich
 
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Question by:Mavreich
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Expert Comment

by:cas1
ID: 7005470
You have to create a separate workspace that refers to your backend. There you can do the same as if you would do in the frontend, even creating tables or adding fields



Set myDBEngine = New PrivDBEngine
Dim wrkJet As Workspace
Dim DBServ As Database
   
myDBEngine.SystemDB = "C:\Test\Test.mdb"

Set wrkJet = myDBEngine.CreateWorkspace("WS", UserName, Password)
Set DBServ = wrkJet.OpenDatabase(C:\Test\Test.mdb", True)
 

Andy
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LVL 3

Expert Comment

by:YP
ID: 7005695
you can do it without creating a workspace as well,
just by adding the database you want to manipulate

for example
database at c:\test
table : mytable
new column : mynewcolumn

ALTER TABLE [c:\test].[mytable] ADD COLUMN mynewcolumn Text(50)

best regards,
yp.
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LVL 58
ID: 7005936
Mavreich,

  As YP indicated, you can do a lot with SQL.  Of course there is always DAO methods as well.  Mostly it depends on the version your using.  It was only from A2000 and up that the SQL support for DML operations was added.

  The on-line help is full of examples.  Here is one:

Sub AlterTableX1()

     Dim dbs As Database

     ' Modify this line to include the path to Northwind
     ' on your computer.
     Set dbs = OpenDatabase("Northwind.mdb")

     ' Add the Salary field to the Employees table
     ' and make it a Currency data type.
     dbs.Execute "ALTER TABLE Employees " _
          & "ADD COLUMN Salary CURRENCY;"

     dbs.Close

End Sub

This example removes the Salary field from the Employees table.

Sub AlterTableX2()

     Dim dbs As Database

     ' Modify this line to include the path to Northwind
     ' on your computer.
     Set dbs = OpenDatabase("Northwind.mdb")

     ' Delete the Salary field from the Employees table.
     dbs.Execute "ALTER TABLE Employees " _
          & "DROP COLUMN Salary;"

     dbs.Close

End Sub


  The MSKB (Microsoft Knowledge base) is also a great source for examples.  Goto support.Microsoft.com.  For example, here's code from one article that shows how to add a Autonumber field via DAO:

      '***************************************************************
      ' FUNCTION: AddCounter()
      '
      ' PURPOSE:  Programmatically adds an AutoNumber field to an
      '           existing table.
      '
      ' ARGUMENTS:
      '
      '    TName: The name of the table.
      '    FName: The name of the new AutoNumber field.
      '
      ' RETURNS:  True (error was encountered) or
      '           False (no error) as an integer.
      '
      '***************************************************************

      Function AddCounter (TName As String, FName As String) As Integer
         Dim DB As Database, TDef As TableDef, Fld As Field

         ' Get the current database.
         Set DB = CurrentDb()
         ' Open the tabledef to which the counter field will be added.
         Set TDef = DB.TableDefs(TName)

         ' Create a new AutoNumber field of type LONG
         ' with the automatic increment attribute.
         Set Fld = TDef.CreateField(FName, dbLong)
         Fld.Attributes = dbAutoIncrField

         ' If you are using version 2.0, replace the
         ' two lines above with the following two lines.
         ' Set Fld = TDef.CreateField(FName, DB_LONG)
         ' Fld.Attributes = DB_AUTOINCRFIELD

         ' Trap for any errors.
         On Error Resume Next

         ' Append the new field to the tabledef.
         TDef.fields.Append Fld

         ' Check to see if an error occurred.
         If Err Then
            AddCounter = False
         Else
            AddCounter = True
         End If

         DB.Close

      End Function

  Anything else you need?

Jim.
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Author Comment

by:Mavreich
ID: 7192285
Hi JDettman and other experts,

Thankyou for you help.  I have had a look at all your suggestions but I am still unable to get it to work.

JDettman your examples are the closet i have got but i am getting hung up on 1 error.  I forgot to mention that the backend is protected by a password.  I have tried every way i can think off to pass the password through when trying to alter the table.  I keep getting an invalid password error.  I know what the password is but can not see where i put it into the above example to get it to work.


Looking forward to your advice.

Regards
Mavreich
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LVL 58

Accepted Solution

by:
Jim Dettman (Microsoft MVP/ EE MVE) earned 1600 total points
ID: 7193355
It's the 'connect' argument of the OpenDatabase method:

Set db = workspace.OpenDatabase(dbname, options, read-only, connect)

The connect string is:

"MS Access;pwd=<password>"  

so your going to do something like this:

Set dbs = OpenDatabase("C:\Program Files\Microsoft Office\Office\Samples\Northwind.mdb",False, False, "MS Access;PWD=northwind")

Jim.
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LVL 2

Author Comment

by:Mavreich
ID: 7194802
Hi JDettman,

This morning I am a very happy man.  Thankyou very much for that example.  Of all the places I tried putting the password that was not one of them.  lol

A Thankyou to you all for your assistance. It is truly appreciated.

Regards
Mavreich
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