Friday, 8 June 2012

Using MS Access Data in a Mail Merge

Suppose you have an Access Database containing the names and addresses of your customers.  Every now and again you may want or need to send a standard letter to each customer who has opted in to such mailings.  However, you are aware that these letters are going to look so much better, and work so much more effectively, if they are personalised to each particular recipient.  A basic example of this is to print the name and address of the customer at the top of the letter, and to include the customers title and surname in the greeting line.   We can go much further than this, of course, and include information about the customers account and even their previous orders (if appropriate).

There are two ways of doing this. We could create an access report which is fine and good. After all, the data is stored in Access, so why not create a the letter by means of such a report?  It is certainly possible to do so.  However, there may well be an advantage in merging your customer data stored in an Access table or query into an MS Word word-processing document.  It is arguably much easier to sit down and compose a well presented standard letter using MS Word (than it is to create the same document in an Access report).  It might be said that Word is a better tool for this particular job.

Mail Merge
The process whereby data from a table is integrated into a word processing document is known as a mail merge.  The following exercise explains how to use information from the Access table in Figure 1 below.

Figure 1: The schema of the Access table we shall be using.
Connecting to Access Data
This first stage in the process involves connecting MS Word to the database where the customer data  is stored. We are going to be working on blank document here, but normally you would begin by composing your standard letter.  The object of this exercise is to show how a Word document gains access to data in an MS Access table or query (rather than how to compose a well presented Word document per se).
  1. Open MS Word.  
  2. Click the SELECT RECIPIENTS icon.  This is located in the START MAIL MERGE group of the MAILINGS ribbon. Clicking the icon reveals a drop down menu.  
  3. Select USE EXISTING LIST from the drop down menu.
  4. Browse to the location of your Access Database (in the window that has opened) and  double click the it's file name.  This opens the SELECT TABLE dialog form in which you see all the tables and queries from your database.
    Figure 2: The SELECT TABLE dialog form.
  5. Double click the name of the table or query containing the customer names and addresses.  We are interested in the tblCustomer. The dialog form then closes.  You are now ready to select which fields to use in your document.

Accessing Table or Query Fields
We have now connected to the Access Database and the table in which the customer data is stored.  The next stage in the process is to insert fields from that table into the actual Word Document itself.  We are going to use fields to enter the customer's address at the top of the letter, and to produce a greeting line.  If we wanted, we could also go further and insert data from the table with the main text of the letter.
  1. Click the location on the document where the field is to be inserted.
  2. Click the lower half of the INSERT MERGE FIELD split button icon.  This is located in the WRITE AND INSERT FIELDS group of the MAILINGS ribbon.  A drop down list of fields appears (see figure 3 below).
    Figure 3: Insert Mail Merge Fields.
  3. Select the customers title field from the list. A title field place holder now appears on the document.
  4. Repeat step 2, this time selecting the surname field.  Make sure you leave a space between the two place holders. 
  5. Go to a new line and then repeat step 2 again, this time selecting the first address field.  Repeat this step for each of the address fields, each field on a separate line.
  6. Go down two  lines below the address fields to enter the greeting line.  Type a greeting such as "Dear ", leave a space, and then insert a title field, followed by another space, and then the surname field
Your document should now look like this:
Figure 4: The Mail Merge Field Placeholders.
Merging Access Data
Once you have added the mail merge fields to your document, you are nearly ready to run the mail merge. Before we do, however, it is a good idea to preview what the documents are going to look like after the data is merged. Do this by clicking the PREVIEW RESULTS icon on the MAILING RIBBON. Each record from the database is then merged onto a separate document. You can scroll through each of these "document records" using the navigation buttons in the PREVIEW RESULTS group. This is how our document looks when previewed:
Figure 5 (above): Preview for the first record of merged data.
Figure 6: FINISH AND MERGE.
We can now run the mail merge. Do this by clicking the FINISH AND MERGE button (see figure 6 above). You are then given the option to PRINT DOCUMENTS or EDIT INDIVIDUAL DOCUMENTS. Doing the latter opens a new instance of Word containing the merged documents. You are then free to make any adjustments that you see fit, and print out when ready.

Saturday, 2 June 2012

VBA Project Anatomy and Scope

Last week I explained how to create an Access VBA Custom Function in a global module.  This was something of a departure from what I covered in previous blog posts.  All of the programming I had covered previously has been associated with a given form or report - what we refer to as a  Class Object.  In this post we are going to take a step back and look at the general structure of a VBA Project as a whole,  and in so doing we will examine the concept and workings of Scope.

VBA Projects
I have mentioned in the past that Access and VBA are two separate, albeit closely related, pieces of development software.  When we create an access database, a VBA project linked to that particular database is created for us automatically.  It is within this project that we create and store all the code relating to our database.

Figure 1: The VBA Project Explorer
showing folders for Class Objects, Modules and
Class Modules.

The VBA project consists of three main elements: these are class objects, modules and class modules. These can be viewed in tree diagram format via the VBA Project Explorer (see Figure 1 right).

Class Objects
Class Objects contain code relating to elements in a  form or report.  We covered these in some detail in the Learning Access VBA series of posts. As you may remember, code from class modules is generally triggered when a form or report event is triggered (for example, the OnCurrent Event is triggered when the user moves into a record displayed on a form).

Modules
Modules, on the other hand are not associated with any particular form or report, but do contain variables, sub procedures and functions that can communicate with them in various ways.  They are a convenient place to keep code which can be read, written to, or called from the class objects.  Moreover, when declared Public, any given variable, sub procedure or function within a Module can be accessed from many different class objects (and sub procedures within class objects) elsewhere in the project.  As such, modules help us organise and manage our code, thereby making our VBA project more logical and efficient. 

Lets elaborate on this further.  Suppose we have a sub procedure called deleteRecord stored in a module.  It purpose is to delete a particular record from a particular table when called.  The advantage of locating this code in a module is so different forms in the database can also make use of this same code.  So rather than  re-write the same section of code in each form, we write it once in a module, and call it whenever one of the forms needs to use it.  As such, we not only write less code, and save time in so doing, but we can easily maintain and modify that code since it is located in one module. That is to say, if we want to change how the  deleteRecord command button behaves in all the sharing forms, we only need update our code in one central place.

Class Modules
So far we have said little about Class Modules, the third main element of a VBA Project.  These are actually worthy of a complete series of blog posts in their own right (something which I may well do in the future). For now, however, let's just say they offer the programmer a way of creating their own custom objects made up of properties, methods and events.  Like conventional modules, class modules also help the programmer organise and manage code, but in a way that is potentially more complex and powerful.

Scope
With the partitioning of class objects, modules and class modules, VBA Projects have the potential to become very large and complicated.  On the one hand these different project 'zones' need to be self contained so something happening in one class module does not interfere with something happening in another elsewhere; yet on the other, they also need to exchange information and communicate.  This is where the concept of Scope comes in.

The concept of scope relates to the way in which different zones of a VBA Project partition the processing of data that occurs within and between each of those sections. We are going to illustrate how this works in relation to variables and sub procedure/function calls. Lets start with how variables behave within a form's object class.

Figure 2:  A basic Class Object to illustrate Scope .

Variables and Scope
The screenshot in figure 2 shows a class object containing two sub procedures, Form_Load() and mySub().  A total of three variables are declared within the class object, two of which, - varB and varC  -are contained within sub procedures. VarA on the other hand is declared above both sub procedures in what is known as the General Declarations section.  The difference in positioning has a direct effect on the scope of each variable.  Let's examine this in more detail.

VarB is declared within the form's Form_Load() sub.  This means the scope of varB is local to this sub, and can only be accessed by code within it.  As such, we can can only read and write to this variable from within the same sub procedure in which it is declared. So, for example, if we assign a value to varB within the Form_Load() sub, we will not be able to read that value from code executed within mySub and vice versa.  This is what is meant by a local variable.

VarA on the other hand is written within the General Declarations section outside of any sub procedure.  The scope of any variable declared here is class object wide.  That is, it can be accessed from anywhere within it's own class object.  As such, we can assigned a value to varA in the Form_Load() sub, and then read that same value externally from mySub.  What we can't do, however, is access the variable from outside of this particular class object.  To do this we need to declare a Public Variable from a Module.

Public Variables
The scope of a public variable declared in a module is project wide - that is to say, it can be accessed from any class object, module or class module in the project.  Public variables are declared using the Public Statement (as opposed to the usual Dim Statement) in the module's General Declarations section (see Figure 3 below for an example).

Figure 3: The shows the Public Variable, varX, in the General Declarations section of Module1.
As you can see, the VBA Project in Figure 3 contains two class objects (Form_frmReadPublicVariable and Form_frmScopeTest) and a module (Module1).  Since the variable varX has been declared with the Public statement in the General Declarations section of Module1, it can be accessed from both class objects.  As such we can assign a value to varX in the Form_frmScopeTest class object, and then read that same value some time later from a sub procedure in Form_frmReadPublicVariable.  However, the disadvantage of using public variables is that they make code potentially more difficult to debug, especially in large projects where the variable might be accessed from sub procedures in many different class objects, modules and class modules.  To some extent we could say that public variables undermine the code management advantages from working in a partitioned VBA project.  That said, they can be a really useful programming tool if used carefully.

Scope and Persistence
Before we move on to look at sub procedure and function calls, it is important to say something about the nature of scope and persistence.  In the context of scope, persistence is how long a value assigned to a variable lasts or persists.  How long, that is, before the variable value is lost and forgotten.  So, for example, if we assigned a value to a local variable declared within a sub procedure using the Dim Statement, that value will persist only as long as the sub procedure is running(1).  Once the sub has finished the value assigned to the variable no longer persists.  Likewise if a variable is declared within the general declarations section of a form class object, any value assigned to the variable will only persist whilst that form is still open.  Once closed the value is lost. Of course it is public variables which have the greatest persistence.  Any value assigned to one of these will last until the database application is closed.

(1) There is an exception to this rule.  We can declare the variable using the Static Statement instead of Dim.  Doing so enables the value to persist, but only within the sub where it has been declared.  The next time that particular sub executes, the previous variable value is remembered and can be read by code (providing that code is still within the same sub).

Scope and Sub Procedure / Function Calls
If you read my post on Writing Custom Functions for Access VBA last week, you may already be familiar with the concept of calling a function.  You may recall how the myPercentage function located in an external module was called from a sub procedure within a form's class object.  You may also recall how we passed three parameters to that function.  The significance of being able to pass parameters in this way, is very important from the perspective of scope.  That is to say, if the calling sub procedure needs to share a local variable with the called function or sub, passing local data in the form of a parameter enables us to bypass the issue of scope.  As such, parameters are a way of letting various parts of the VBA project share information and communicate without compromising the real need to keep the project strictly partitioned in an organised manner.

Lets examine a simple example of how passing a parameter, this time in a sub procedure call, can bypass the issue of scope:

Private Sub Command9_Click()
    Dim varThis As Integer
    varThis = 10
    Call thatSub(varThis)
End Sub


Private Sub thatSub(argReceived As Integer)
    MsgBox ("The argument received is: " & argReceived)
End Sub


Here we have two private sub procedures within the a form's class object.  When the user clicks a command button, the Command9_Click sub procedure begins to run.  It defines a local variable called varThis and assigns it with the integer value 10.  The next line calls the thatSub sub procedure, passing the local variable varThis as the parameter.  This call results in the execution of thatSub.  Notice how the first line of thatSub contains the code argReceived As Integer within brackets.  This is where the passed parameter (varThis) is received by the called sub procedure.  The parameter which has been passed is now referred to as an argument, and it's value can be accessed from code within the receiving sub procedure.  As such, when the second line of code in thatSub runs, a message is displayed ending with the value contained in argReceived (see figure 4 below).  

Figure 4: The message displayed from the
 MsgBox method in thatSub.
We see, therefore, that the value contained in what is a local variable has been passed to a different sub procedure which would otherwise have been outside that variable's scope.

Conclusion
In this post we have seen how the VBA project is partition into various zones, and how those zones are largely self contained in terms of data processing.  This partitioning is maintained via a set of rules collectively known as scope, the advantage of which is the management of code within the project.  Since there is a legitimate requirement for these zones to exchange information, the working of scope can be bypassed in a managed manner through the passing of parameters and receipt of arguments.


Friday, 25 May 2012

Writing Custom Functions for Access VBA

VBA Custom Functions work in a similar way to any inbuilt MS Access Function.  Both types can be called within VBA sub-procedures1, and then return a value for the function's 'result'.  Take the inbuilt DLookUp function, for example.  This is written as follows:

varResult = DLookUp ( parameter1, parameter2, parameter3 )

Three things happen when we call this function:
  1. The function is called using VBA code (passing three parameters in the process), 
  2. The function looks up information stored in an access table (based on the parameters passed), 
  3. It then returns that information, storing the result in a variable called varResult.  
On account of DLookUp being a built in function, we do not get to see what happens in stage two.  Custom Functions are different in that we actually write a block of VBA code that executes at that stage.  Once we have set this up, we can call our custom function as often as we like.  Moreover, because custom functions tend to be located in a VBA global module, and declared as 'Public' in scope, they can be called from multiple points within our application. In this way, the creation of custom functions make our programming more organized and manageable.

Figure 1:  This screenshot of the VBA Project Explorer shows
 a module call modCustomFunction.  Providing the custom functions contained within are
declared 'public' they can be called from anywhere within the project  - such as
the form which I have called frmFunctionDemo.

How to Create a Custom Function
When we create a custom function we need to write the code that executes once it has been called from a sub procedure. As we shall see, this code is structured in a similar manner to an ordinary sub.  However, we also need to include a line of code which specifically returns a value back to the calling code. This is done by assigning a value to the name of the function (in a similar manner to assigning a value to a variable). For example:

Public Function myPercentage(argScore As Integer, argOutOf As Integer)
        myPercentage = (100 / argOutOf) * argScore 2
End Function

This creates a function called myPercentage.  The first line of code declares the function, and receives two arguments from the calling code ie argScore and argOutof.  The second line of code in this example returns the result of the myPercentage function.  There can any number of lines of code preceding the returning line.  However, I have provided a simple example which returns the result of the function in the same line of code as a percentage calculation.  This code is stored in a global module called modCustomFunctions (see Figure 1 above). 

Here is the code I have used to call this function:

Private Sub cmdCalculate_Click()
    Me!txtPercentageResult = myPercentage(Me!txtScore, Me!txtOutOf)
End Sub

This code executes when a form command button (cmdCalculate) is clicked by the user.  The function (myPercentage) is called in the second line of code.  As you can see, the calling code for myPercentage passes two parameters, the values of which reference two text box controls - txtScore and txtOutOf.  The function uses these parameters (which are received as the arguments argScore and argOutOf) to calculate the percentage and return the result.  The result is then displayed in a third text box called txtPercentageResult.

Figure 2: This is the form from which our function is called.  The CORRECT ANSWERS textbox is called txtScore, No OF QUESTIONS is called txtOutOf, and the PERCENTAGE textbox is called txtPercentageResult.  The CALCULATE button is called cmdCalculate

Figure 3: The top window shows the code calling the myPercentage function.  The lower window shows the code from the myPercentage function itself.   

Footnote

1/ It needs to be pointed out here that the inbuilt functions of MS Access can be can be called from within Access itself (eg within the Query Design Grid as a criteria, or to populate a calculated control on a form etc), and not just from within VBA.  Custom functions, on the other hand, can only be called within VBA. 

Friday, 18 May 2012

Your Feedback?

I have been writing the MS Access Tips blog around three years, and it is now being read by hundreds of people each day. I am very interested to learn more about who is reading my blog, and and what people think about it.  I would be really grateful if you could take the time to answer 6 simple question in a survey that I have set up for this purpose.  This will help me to continue writing articles that are relevant and interesting to you, the readers.

Please click the link below to begin the survey.  Many thanks.

Survey for the MS Access Tips Blog

Friday, 11 May 2012

Using the Make Table Query to Collect Archive Data

Information stored in a database is likely to change over time.  When details change, data may be overwritten, and once this happens it is lost.  There are certain scenario's where it is important to have access to 'historic' data, by which I mean a snapshot of information which was stored in the database at a given point sometime in the past.  Let's take an Order Management System for example.  Suppose you need to find a customer contact name from two years previous?  If the customer in question happened to be an organisation or business, it is possible that there was a different person in post at that time.  In this case, it would be useful to have some facility to access data from that point in time.  Whilst we can't create this sort of archive from the present backwards,  we could have taken a snapshot of this data at periodic intervals previously.  One way of doing this was to have created a Make Table Query to extract relevant data from the database with a query and store the results in a new table.  These can then be saved in a separate archive database ready to be accessed if and when needed.

Taking the Order Management System scenario, there is data stored in four related tables, and only certain  fields from each table need to be archived.  We could simply make a copy of each of the four tables, but this would result in the storage of unnecessary information.  It would also be less convenient to access at a later point in time.

The related tables in question are tblCustomer, tblOrganisation, tblPerson and tblAddress.

Figure 1: The Make Table Query for an Order Management System.

Creating a Make Table Query
Before we create the Make Table Query, you might like to create a new blank database file.  This is so we have a separate database into which we can paste the new table from the query.  In this exercise I have called it HistoricData.accdb.

Here is the procedure to create a Make Table Query:
  1. Open the database which we are going to query (In my case this is the Order Management System).
  2. Click the QUERY DESIGN icon (located in the OTHER group of the CREATE ribbon).
  3. Select the tables to be used from the SHOW TABLE dialog form. I have selected  tblCustomertblOrganisationtblPerson and tblAddress.
  4. Next select all the fields from the existing tables to be used in the query.  These not only form the query results, but also the structure for the new table.  I have chosen fields from all four tables so that the new table will be self sufficient. 
  5. Amend the table relationships (or Joins) as required.
  6. Click the MAKE TABLE icon (located in the QUERY TYPE group of the DESIGN ribbon).  This opens the MAKE TABLE dialog form (see Figure 2 below).
    Figure 2: The Make Table Dialog Form.
  7. Enter the name of the new table that we are going to create.  I have called mine tblCustomerTeamsMay2012.
  8. Click the option button for ANOTHER DATABASE. This ensures the new table will be created in a different database.
  9. Browse to the location of the external database.  I have called mine HistoricData.accdb.  Double click the file to select and then click OK to close the dialog form.
  10. Test the Query by clicking the DATASHEET VIEW icon (located in the RESULTS GROUP of the DESIGN ribbon).
  11. If you are happy with the data displayed, you can run the Make Table Query by clicking the RUN icon (located in the RESULTS group of the DESIGN ribbon).  This will now create the new table in the external database.
You can now open the external database and view the newly created table:

Figure 4: The newly created tblCustomerTeamsMay2012 table (Design View).

Now all the database administrator has to do is run this query every month, changing the new table to the appropriate month.  Over time, we collect a 'warehouse' of data ready to be accessed if and when needed.  Since this data is stored in a separate database, it does not impact upon the performance of the actual system from which the information was collected.

Friday, 4 May 2012

Using the Access Database Splitter

Last year I wrote a post on Linking to an External Data Source.  This is where we split an Access database  into a Back End (which stores all the tables and data), and a Front End (which contains all the forms, queries and reports).  There are a number of advantages to observing this practice.  To begin with, splitting a database file in this way is all but essential if it is to be deployed on a network in a multi-user environment. Another big advantage is that we can easily replace a front end file with a new updated version with minimal disruption - the actual data stored in the back end tables is not touched in this process. 

If you read the my post last year, you may remember that I showed you how to link a front end Access file to an existing back end database.  This is fine if the back end database already exists, or if you decide to create the application in two separate files from the start.  However, many developers create or inherit a complete database application as one stand alone file, and then proceed to split the database.  Splitting the database can be done manually, but this is often time consuming and there is always the possibility of making errors in the process.  An easier and quicker way of doing this is by using the Access Database Splitter.  This is a wizard that splits the database into a front and back end, as described above.  

Splitting an Access Database
The database that I am working with here is an Order Management System containing a number of tables.  If you want to try this on one of your own database files, it does not matter how many tables it contains - it could have a hundred or it could just have one.  
Figure 1
  1. Click the ACCESS DATABASE icon (located in the MOVE DATA group of the DATABASE TOOLS ribbon).  See figure 1 on on the right.  This opens the DATABASE SPLITTER Wizard.
  2. Click the SPLIT DATABASE button at the bottom of the Wizard (see figure 2).   
  3. You are now asked to select one of your folders for the new back end Access file.  Browse to a location of your choice, enter a back end file name, and then click SPLIT.  After a moment or two, you should get a message box saying "Database Successfully Split".
  4. Click OK.
Figure 2: The Database Splitter Wizard from Stage 2.
You can now look at the navigation pane of the front end database and see the linked tables (see figure 3).  You can try adding data to one of your tables and then open the back end file to see it stored there.  You could also try copying the front end file in order to access the back end tables with different front ends.  In so doing you can see the basic principle behind how multi-user systems operate*.
Figure 3 (above): This is how linked tables appear in the Front End Database file.
Figure 4:  Your Database is now split into two files one for the front end and one for the back end.

*Tip:  If you want to run more that one Access front end at a time, you will need to open multiple instances of the Access Database.  So rather than clicking on the access front end file directly (ie from within Windows Explorer), you should open Microsoft Office Access from the windows START button or DESK TOP and then open each front end file from the GETTING STARTED WITH MICROSOFT OFFICE ACCESS screen.   

Friday, 27 April 2012

Hiding the Navigation Pane with VBA

Once you have created an Access Database Application to be used by other people, it may well be important for you to prevent users from gaining access to any of its design features.  By this I mean, you may not want users to modify your tables, forms and queries etc in design view (inadvertently or otherwise).  There are a number of measures you need to take in order to secure your database against this possibility.  One of these involves preventing users from accessing the NAVIGATION PANE, a major doorway to all of your database objects.  Hiding the NAVIGATION PANE can be done with a couple of lines of VBA Code.

To use this code, you will need one of your database forms' to open automatically as your application opens. There are instructions to do this in my post on How to Display a Form Automatically. Once this is in place you can insert the following code into that form's ON LOAD event.

    DoCmd.SelectObject acTable, "tblCustomer", True
    DoCmd.RunCommand acCmdWindowHide 


The purpose of the first line of code is to select any object in the navigation pane.  We have selected one of the database tables called tblCustomer, and then set the INNAVIGATIONPANE parameter to true.  Once  a database object from the navigation pane has been selected, we can then use the DoCmd.RunCommand with the acCmdWindowHide parameter in the following line of code.  This has the effect of hiding whichever window happens to contain the selected object. 

The user can quite easily get the Navigation Pane back by pressing the F11 Access Special Key (assuming  that he or she knows about it), but this facility can be disabled.  To do this you will need to deselect the USER ACCESS SPECIAL KEYS check box in the CURRENT DATABASE section of ACCESS OPTIONS, (via the OFFICE button).

Hiding the Navigation Pane alone is not sufficient to secure a database, but it is one important part of doing so.