How to Use the ODBC Driver with “How To” Article

How to Use the ODBC Driver with
NDS, Part 4: Example Application
“How To” Article
NOVELL APPNOTES
Joshua Parkin
Software Engineer
NamSys Inc.
jparkin@home.com
This AppNote, the fourth in a series, demonstrates the creation of an application
that takes an SQL query through the ODBC driver for NDS and build an XML
file. The article includes an example application.
Contents:
72
•
Introduction
•
Expanding on Well-Formed XML and More Review
•
Starting a New Visual Basic Project
•
Notes on Usage
•
Conclusion
Topics
database connectivity, directory-enabled applications,
ODBC, third-party product integration
Products
Novell Developers Kit, NDS eDirectory (all versions)
Audience
developers, integrators
Level
intermediate
Prerequisite Skills
familiarity with database programming and ODBC
Operating System
NetWare 4.x or 5.x
Tools
none
Sample Code
yes
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Introduction
The previous article in this series dealt with the theory of XML, including
namespaces and well-formed XML (http://www.developer.novell.com/research/
appnotes/2001/April/05/a010405.htm). This article will demonstrate how to
create an application that takes an SQL query through the ODBC driver for NDS
and builds an XML file with the resulting set.
Remember that an XML file is built in a pseudo-tree structure. You should have a
root tag followed by a container tag, which should contain element tags. You will
see examples of XML files throughout this article. Later on, I will discuss
well-formed XML in greater detail.
One of the main advantages of XML is the ability to use XML files to send and
merge data. The only major disadvantage to using XML files this way is tag name
conflicts. To solve the problem use namespaces. Namespaces are used to
segregate your XML tags from those of someone else, even if they have the same
name. Namespaces can be anything you choose, such as your favorite food or
your Web site.
Expanding on Well-Formed XML and More Review
If you plan to convert anything to XML, you must carefully plan the XML file.
Make certain it is well-formed and conforms to the XML rules, so the data is
interchanged among the platforms without error.
Remember what has been learned about XML. You know you need to have the
<?XML version="1.0"?> included in the first line of the file. At this time, I will
not be concerned with international languages. I will assume that everything will
be kept in English and that there is no need to put in any language features. Now,
you need to plan a root node. An XML document needs this root. I’ll have the root
node named <NDSTree>. This is the file layout so far:
<?xml version="1.0"?>
<NDSTree>
-information from the NDS tree
</NDSTree>
Now, I will talk about node names. For now, it is easiest to use the actual node
names from the tree. That means you need to decide which nodes you will use.
For the purpose of this article, I will assume that you are going to make an XML
file that contains a corporation’s contact information on a Web page:
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NDS_FullName
•
Title
•
Postal Address_Street
•
Postal Address_POBox
•
Postal Address_State
•
Postal Address_Street
•
Postal Address_ZIP or Postal Code (This is up to you and where you are).
•
Telephone Number
The XML File
So far, you have designed an XML file with all the important parts. The following
is an example XML file.
<?xml version="1.0"?>
<NDSTree>
<NDS_FullName>info</NDS_FullName>
<Title>Info</Title>
<Postal Address_Street>Info</Postal Address_Street>
<Postal Address_POBox>Info</Postal Address_POBox>
<Postal Address_State>Info</Postal Address_State>
<Postal Address_Street>Info</Postal Address_Street>
<Postal Address_ZIP>Info</Postal Address_ZIP>
</NDSTree>
Writing a Visual Basic program to Populate the XML File
The file you have created is missing something. There is a root object and some
leaf objects, but, since there will be multiple entries, there must also be a leaf
object that contains all the individual’s data. Call it <NDSObject>. You have just
planned what may be your first XML file. It is well-formed and contains all the
important information, but the file is useless until it is filled with the appropriate
data. To avoid entering all the employee’s information in the fields yourself, you
need to build a conversion program that will grab the important information and
store it in the file.
Starting a New Visual Basic Project
In order to develop this conversion program, you need to run Visual Basic and
start a new project. First, go to the Project References and select DAO Library
3.51. I cannot stress this step enough. You may spend hours debugging if you
don’t select this option. Also, if this option is not selected, the help button on the
error screen will not tell the user to look at the DAO Library option. Save yourself
a headache and do this first. Figure 1 shows this option selected.
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Figure 1: Selecting the Microsoft DAO 3.51 Object LIbrary.
Designing the Form
Next, design the form layout. For this project, you need to add three command
buttons, two list boxes , one combo box, one text box, and some labels that will
give some indication of what each control will do. The layout could look
something like the one shown in Figure 2.
Figure 2: Sample Form Layout.
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One other thing you need to add is a common dialog box. This is used for finding
out where the user wants to save the files. The textbox is for the user to enter a
field name. The combo box will be populated with the object in the tree. One of
the list boxes, list1, will be populated with the objects contained in the object the
user chooses in the combo box. The other list box, list2, will display the selected
objects to be used in the file. One command button, command1, will be used to
add the selected objects from list1 to list2. Command2 will be used to allow the
user to build the application. The command3 button will allow the users to clear
list2.
Writing the Form’s Code
Now, program the form. First, disable the buttons. This will stop the user from
being able to use them when the buttons have nothing to do. A data control was
not used because the PullTree function created in part 2 of this series will be used
instead. (You can find “How to Use the ODBC Driver with NDS, Part 2” in the
December 2000 issue of Novell AppNotes at http://developer.novell.com/
research/howto.htm.)
The function’s code is as follows:
Public Function PullTree(sqlQuery As String, tmpTree As String, tmpDSN As String)
'See if the database is already open and if so close it
If Not (NDSTree Is Nothing) Then
NDSTree.Close
End If
If tmpDSN = "" Then ' See if DSN -less connection
Connect = "ODBC;Driver={Novell ODBC Driver for NDS};DSN=;DBQ=" + tmpTree + ";"
Else ' DSN connection
Connect = "ODBC;DSN=" + tmpDSN + ";DBQ=" + tmpTree + ";"
End If
Set NDSTree = OpenDatabase("", False, True, Connect)
Set NDSrs = NDSTree.OpenRecordset(sqlQuery)
End Function
The PullTree function can be placed in a separate module or right into your frame.
The choice is yours, depending on how your application works. In this tutorial,
you can simply put it in your frame. Next, create the variables needed in order to
use the PullTree function. They are as follows:
Public NDSTree As Database
Public NDSrs As Recordset
Public recCount As Integer
These global variables are used by the function and need to be passed throughout
the application. They are to be defined in the Declarations portion of your code.
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In the form load section you must open the database and pull out the fields needed
to populate the combo box, combo1.
Private Sub Form_Load()
Connect = "ODBC;Driver={Novell ODBC Driver for NDS};DSN=;DBQ=gennexx;"
Set NDSTree = OpenDatabase("", False, True, Connect)
' Fill the Table combo Box
For I = 0 To NDSTree.TableDefs.Count - 1
Combo1.AddItem NDSTree.TableDefs(I).Name
Next I
End Sub
Open the database using a DSN-less connection and use the tabledef property of
the NDSTree object to pull out field (object) information. There is no need to run
an SQL query because you are simply doing a general scan of the database and
grabbing the appropriate properties. You do not need to create a recordset at this
time because you are not pulling field values out of the tree. You are simply
grabbing the fields contained in the tree.
If the program is run now, you will see the combo box populated with all the
objects contained in that tree. Now you are able to browse through and select the
appropriate object from which you want to grab info for the XML file . However,
in order to make it worthwhile, you will need to code the combo box to do
something when chosen. Use the click event.
Private Sub Combo1_Click()
Dim varQuery As String
Dim varTree As String
Dim varDSN As String
Dim ndsTableDef As TableDef
'dsnless connection
varDSN = ""
'sql query
varQuery = "SELECT [NDS_Name] FROM " & Combo1.Text
'tree name
varTree = "gennexx"
'calls the function to open the database to play
Call PullTree(varQuery, varTree, varDSN)
'populates the list box
Set ndsTableDef = NDSTree.TableDefs(Combo1.Text)
For I = 0 To ndsTableDef.Fields.Count - 1
List1.AddItem ndsTableDef.Fields(I).Name
Next I
End Sub
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Note: Here you will use the PullTree function that was created in part 2 of this
series. You are going to use DSN-less connection. For the SQL statement
you will use the combo1.text property to make sure you grab the
appropriate information from the right object in the tree. Since the
function opens the database and builds an appropriate recordset, use the
tabledef property again in order to grab the field names inside that
object and put them into List1.
Now, functionality must be given to the command buttons.
Private Sub Command1_Click()
'add button
List2.AddItem List1.Text
End Sub
Private Sub Command2_Click()
'build button
'If text1 is blank then notify user and make them enter a name.
If text1.text = "" then
Msgbox "You need to enter a file name, no extension please."
Else
Call buildFile()
End If
End Sub
Private Sub Command3_Click()
'clear button
List2.Clear
End Sub
Now, for the piéce de résistance: the buildFile function. This function needs to do
several things, but first get the location and filename to write to. Otherwise, you
will get an error when you try to open and write. Also, run the query from the
recordset (from pullTree) and then build the file as laid out above.
Start thinking about how you are going to build this function. First, name it.
Public Function buildFile()
End Function
Okay, that was the easy part. Now you need to call upon the common dialog box
that was put on the form. If you have not done so, you should do that now. I
named mine NDScmdlg. Therefore, I have to add the following lines of code:
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On Error Goto CancErr
With NDScmdlg
.CancelError=True
.Filter = "XML files|*.xml|"
.ShowSave
End With
On Error Resume Next
CancErr:
If err.number=32755 then Exit Function
Note: I put in an error checker in case the user canceled the operation. If the
user does cancels the operation, it will send back an error (#32755).
Next, you will access the file system object and open the file for writing.
Dim fso, f, ts
Const ForReading = 1, ForWriting = 2, ForAppending = 8
Const TristateUseDefault = -2, TristateTrue = -1, TristateFalse = 0
Set fso = CreateObject("Scripting.FileSystemObject")
Set f = fso.GetFile(NDScmdlg.FileName)
Set ts = f.OpenAsTextStream(ForWriting, TristateFalse)
Write the first lines to the file. These is the <?XML?> tag and the root node tag.
Ts.WriteLine "<?XML version=""1.0""?>"
Ts.WriteLine "<NDSTree>"
Note the use of double quotations in the <?XML?> tag. The reason for it is that
VB will now know to insert into the string a single quotation mark where each of
the double quotations exists. Otherwise, VB is looking for a variable named 1
with property name 0, which you know cannot exist. This generates a really nasty
error.
The file is now open, and you have started to write to it. So, now what? You can
call upon the PullTree function to retrieve the recordset. First thing you need to do
is DIM the appropriate variables needed for the pulltree function.
Dim varTree As String
Dim varSQL As String
Dim varDSN As String
Since you are going to need to know the number of records pulled from the query,
there must be another variable.
Dim numofRecs As Integer
Next, you will build the query.
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varSQL = "Select "
If List2.ListCount > 1 Then
For i = 0 To List2.ListCount - 2
varSQL = varSQL + "[" + List2.List(i) + "], "
Next
varSQL = varSQL + "[" + List2.List(List2.ListCount - 1) + "] "
varSQL = varSQL + "From " + Combo1.Text
Else
varSQL = varSQL + "[" + List2.List(List2.ListCount - 1) + "] "
varSQL = varSQL + "From " + Combo1.Text
End If
Check to see how many items are selected. If there is only one selected, then build
the statement with one entry. Otherwise, there needs to be a comma between the
fields in the SQL query. That is why there is the routine that puts the last field in
the list without a comma at the end. If this were not there, you would get an SQL
syntax error.
Next, define the rest of the variables used for the pullTree function and call the
function.
varTree = "[treename]"
varDSN = ""
'call the PullTree function to run the SQL query
Call PullTree(varSQL, varTree, varDSN)
Here, you are going to use a DSN-less connection again. The choice is yours. All
you have to do is put in a tree name. Next, count the number of records returned
from the query and loop to write that many records into the file. For each object
returned, start a new object in the XML file. Before the information regarding that
object is written to the file, write the <NDSObject> tag. Write the field names as
the tags for the returned objects. When it is all done, close with a </NDSObject>
tag.
NDSrs.MoveLast
numofRecs = NDSrs.RecordCount
NDSrs.MoveFirst
'loop for the number of records
For x = 1 To numofRecs
ts.WriteLine "
<NDSObject>"
'loop for the number of fields pulled
For i = 0 To List2.ListCount - 1
If NDSrs(List2.List(i)) = Null Then
ts.WriteLine "
<" + List2.List(i) + "></" + List2.List(i) + ">"
Else
ts.WriteLine "
<" + List2.List(i) + ">" + NDSrs(List2.List(i)) + "</" +
List2.List(i) + ">"
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End If
Next
ts.WriteLine "</NDSObject>"
NDSrs.MoveNext
Next
NDSrs.Close
ts.Close
There you go. You have written an XML converter for the NDS tree. It’s pretty
simple, isn’t it?
So, what is next? Well, in case you didn’t notice, there are some problems with
the program. For instance, the tags have spaces in their names. This must be fixed,
and the easiest way is to replace the spaces with underscores. However, to make
the program much more functional, you can allow users to name their own XML
tags instead.
To allow for this, add a new function named tagNames. Pass a variable to it with
the number of fields in the list. The function code will look like this:
Public Function tagNames(tmpNum As Integer)
End Function
Also, create a variable to store the new tag names to. Limit the total number of
tags to 1000. That means there is a limit to the total number of objects you can
pull for each entry in the tree. One-thousand should be sufficient for now. You can
increase or decrease the limit amount as you see fit. The variable, varListCount, is
there only to keep track of how many records were selected.
Private vartagNames(1000) As String
Public varListCount
Now, you can build the function. The function will use the input box function to
grab the input from the user.
Public Function tagNames()
For i = 0 To varListCount -1
tmpName = InputBox("Enter the tag name to represent" + List2.List(i))
if tmpName = "" then msgbox "You must enter a tag name!"
vartagNames(i) = tmpName
Next
End Function
Figure 3 shows an example input box.
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Figure 3: Example Input Box.
Now, call it from the BuildTree function. You will need to add the tmpNum as
well. Since this is used for the loop to build the appropriate number of tagnames,
use the number of records chosen for the field (list2.listcount) and add that to
varListCount.
VarListCount = list2.listcount
Call tagNames
Of course, this begs the question: How do you put the tagnames into the file when
the buildTree function just puts in the list2.text values? You will need to change
that module slightly. Look at the loop and make the appropriate changes.
For x = 1 To numofRecs
ts.WriteLine "
<NDSObject>"
'loop for the number of fields pulled
For i = 0 To List2.ListCount - 1
If NDSrs(List2.List(i)) = Null Then
ts.WriteLine "
<" + vartagNames(I) + "></" + vartagNames(I) + ">"
Else
ts.WriteLine "
<" + vartagNames(i) + ">" + NDSrs(List2.List(i)) +
"</" + vartagNames(i) + ">"
End If
Next
ts.WriteLine "</NDSObject>"
NDSrs.MoveNext
Next
Now you have implemented code that will allow the user to create whatever tags
he or she wishes as the file is being created.
Notes on Usage
Keep in mind the size of the returning recordset. If it is excessively large, you may
need to create a significantly large XML file. Remember, you can break down the
tree using SQL queries to fit whatever criteria you are looking for. (See the
AppNote series on “How to use the ODBC driver for NDS,” as previously
mentioned.)
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Currently, the program does not check to see if the file chosen already exits. If it
does, the existing file will be automatically overwritten. To change this feature,
implement a check using the File System Object’s check FileExists.
Another thing the program does not handle is NameSpaces. This means that if you
were to generate two files with the same node names and merged the two, you
would run into some problems. The XML parser (whichever you used, be it DOM
or XSL) wouldn’t know which one to use. This is easily remedied. You should
implement a check for the special characters that were mentioned before. This
check can be done by doing an INSTR function and replacing the text using the
MID function. This would be important if you did not know what the fields
contained. If you were doing a query that you were certain did not have such
character as <, >, &, or ”, then you wouldn’t have to worry about it. But you never
know, and that is why I have brought it to your attention.
Conclusion
XML is being implemented everywhere. More and more tools arrive on the scene
each day. To keep up with everything, I recommend http://www.xml.com/. This
site provides the most unbiased up-to-date information regarding XML. They
keep track of what’s going on with XML, including what the W3 consortium has
implemented, their working papers, and more. It also examines the new
technology that is coming out regarding XML and how it works. There are also
examples and definitions of the different features of XML. Quite often, you will
find tutorials on how to use EJB (Enterprise Java Beans) with IBM’s WebSphere
product and how to use Microsoft’s DOM to generate web pages. You will also
find a regular column discussing what’s new in parsers and how each stands up to
the standards set by the consortium. The web site is updated weekly, so you are
not left in the dark regarding any of the developments. This is always a good
resource and a terrific place to start.
WROX is coming out with a Professional XML book that is supposed to be huge!
I haven’t seen it, yet, but word on the street is that it is excellent and covers
everything regarding XML to date.
Keep up to date regarding this exciting development by using the aforementioned
resources, and let your creative juices flow. This is the ground floor and there is
lots of room to grow with this exciting new technology.
Copyright © 2001 by Novell, Inc. All rights reserved.
No part of this document may be reproduced or transmitted
in any form or by any means, electronic or mechanical,
including photocopying and recording, for any purpose
without the express written permission of Novell.
All product names mentioned are trademarks of
their respective companies or distributors.
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