Recipe 10.5 Programmatically Track Users and Groups

10.5.1 Problem

As the database administrator, you want to be able to track users and their groups within your workgroup. How can you gather the information you need?

10.5.2 Solution

Using Data Access Objects (DAO), you can retrieve all the information you need about users' names and groups. Once you have that information, you can use it in creating your applications.

The sample form frmUserGroups in 10-05.MDB fills tables with the information you need and presents it to you in a list box. To test it, open and run frmUserGroups. Figure 10-20 shows the form in use for a sample workgroup.

Figure 10-20. frmUserGroups shows users and groups for a sample workgroup

To gather this information in your own applications, follow these steps:

Table 10-13. Table layouts for gathering user/group information

Table name	Field name	Field type	Primary key?
tblGroups	Group	Text	No
	GroupID	Counter	Yes
tblUserGroups	UserID	Number (Long Integer)	Yes
	GroupID	Number (Long Integer)	Yes
tblUsers	UserName	Text	No
	UserID	Counter	Yes

Table 10-14. Index settings for tblGroups

Index name	Field name	Sort order
Group	Group	Ascending
PrimaryKey	GroupID	Ascending

10.5.3 Discussion

This solution relies on the DAO object model to gather its information. The DBEngine object is at the root (the highest level) of the DAO object hierarchy, and it has a single collection, the Workspaces collection. Each workspace represents a session of the Access database engine (and unless you're writing sophisticated applications, you'll most likely never see more than a single concurrent workspace). The default workspace contains information about the collection of open databases (only one is open in the user interface—all others must be opened via VBA code) along with the available user and group collections. These are the collections you'll need for filling tables with the usernames and their groups. The code in the acbListUsers subroutine does all the work.

The acbListUsers function starts out by setting up object variables to refer to several recordset objects, and refreshes the Users and Groups collections of the workspace. This is necessary to make sure we see any recent changes to these collections made via the Access user interface or by another Access session. The relevant code is:

' Set up object variables.
Set wrk = DBEngine.Workspaces(0)
Set db = wrk.Databases(0)
Set rstUsers = db.OpenRecordset("tblUsers")
Set rstGroups = db.OpenRecordset("tblGroups")
Set rstUserGroups = db.OpenRecordset("tblUserGroups")

' Refresh the Users and Groups collections
' so we see any recently added members
wrk.Users.Refresh
wrk.Groups.Refresh

The next step entails deleting all the existing rows in the three tables, using the Execute method of the database object:

' Clear out the old values
db.Execute "DELETE * FROM tblUserGroups"
db.Execute "DELETE * FROM tblUsers"
db.Execute "DELETE * FROM tblGroups"

Once these lines of code have executed, the three tables will be empty.

The next step is to build up a list of all the groups. This is accomplished by looping through all the elements of the workspace's Groups collection. Just like all other collections in Access, the Groups collection provides a Count property indicating how many elements it contains. These items are numbered from 0 through Count-1, and we loop through them all, adding a row to tblGroups for each group in the collection:

' Build up a list of all the groups in tblGroups
For intI = 0 To wrk.Groups.Count - 1
    rstGroups.AddNew
        rstGroups("Group") = wrk.Groups(intI).Name
    rstGroups.Update
Next intI

Once tblGroups is filled in, we do the same for users. Just as the workspace contains a collection of groups, it also contains a collection of users. We can walk through the Users collection, adding a row at a time to tblUsers, as shown here:

    ' Loop through all the users, adding
    ' rows to tblUsers and tblUserGroups.
    For intI = 0 To wrk.Users.Count - 1
        ' Add a user to tblUsers.
        Set usr = wrk.Users(intI)
        rstUsers.AddNew
        rstUsers("UserName") = usr.Name
        rstUsers.Update
        rstUsers.Move 0, rstUsers.LastModified
    
        ' See the next code example...

    Next intI

Once a user is added, rows are added to tblUserGroups for each group that contains the current user. This is accomplished by enumerating through the Groups collection for the current user. (Note that there was a choice here. Each member of the workspace's Users collection has its own Groups collection, listing the groups to which it belongs, and each member of the workspace's Groups collection has its own Users collection, listing the members of the group. The code can either walk through the users, looking at the Groups collection in each, or walk through the groups, looking at the Users collection in each. This example walks through the workspace's Users collection, one at a time, studying the Groups collection in each one.) The following code loops through every item in the user's Groups collection, finding the matching name in tblGroups, and then adding a row to tblUserGroups containing both the user's UserID field (from tblUsers) and the GroupID field (from tblGroups). This way, tblUserGroups contains a single row for every user/group pair. The code is:

' Now loop through all the groups
' that user belongs to, hooking up the rows
' in tblUserGroups.
For intJ = 0 To usr.Groups.Count - 1
    rstGroups.Index = "Group"
    rstGroups.Seek "=", usr.Groups(intJ).Name
    If Not rstUserGroups.NoMatch Then
        rstUserGroups.AddNew
            rstUserGroups("UserID") = rstUsers("UserID")
            rstUserGroups("GroupID") = rstGroups("GroupID")
        rstUserGroups.Update
    End If
Next intJ

Once the code has looped through all the users and all the groups to which each user belongs, it closes all the objects:

rstUsers.Close
rstGroups.Close
rstUserGroups.Close

Now tblUsers, tblGroups, and tblUserGroups contain information about each user and the groups to which he or she belongs.

Once you've filled the three tables, you can easily perform lookups in your VBA code or create reports displaying security settings. You could also just lift pieces of the code from acbListUsers for use in your own applications. The next solution shows a simpler function, acbAmMemberOfGroup, which uses a similar technique to query on the fly if the current user is a member of a specific group.

The acbListUsers procedure is not production-quality code. To keep it simple, we left out the error-handling code, and any procedure of this nature that manipulates tables must include sufficient error-handling capabilities. Though it's not likely, some other user may have locked the output tables or, worse, deleted them, or you may not have permissions for the system tables you need in order to gather this information. In a production environment, it's best to trap errors and handle them.

In the list of users found in tblUsers, notice that there are two users that you might not have seen before: Creator and Engine. These two users are created by the Jet engine itself and cannot be used or manipulated by VBA code. As you'll see in the Solution in Recipe 10.7, you can create a Workspace object for any normal user, allowing that user to log into a new session of the Jet engine, but you can't use Creator or Engine to create new workspace objects. It's a good thing, too! Since neither can have a password (their passwords are always blank), this would otherwise provide a security breach. Because you can neither log on manually nor log on using the CreateWorkspace method with either user, these two special users don't pose a security risk.

Once you know how to enumerate through collections, as shown in this solution, you should be able to apply the same techniques to other database collections and their objects. For more information, see Chapter 4.