Friday, December 27, 2019

The Heart Break of Code Wadding

Some issues with interface design for Relational Database Applications come up over and over again.

One of those is the problem of adding new records in a junction table. Here's what the tables look like. The junction table, called tblArtist_Songs in this example, joins artists and the songs they've recorded in a Many-to-Many Relationship.
Artists, Songs and Recordings of Songs in a Junction Table
  • Each artist can record one or more songs.
  • Each song can be recorded by one or more artists.
  • Each recording of a song by an artist occurs in a particular year.
Less experienced MS Access developers frequently try to create a query including all three of these tables to serve as the recordsource for a single data entry form. Something like this would be a typical result. It would be bound to a single form to manage artists, songs and records all in one.

, tblArtist.Artist
, tblArtist.ArtistGroup
, tblArtist_Songs.ArtistID
, tblArtist_Songs.SongID
, tblArtist_Songs.YearRecorded
, tblSong.SongID
, tblSong.Song
(tblArtist INNER JOIN tblArtist_Songs ON tblArtist.ArtistID = tblArtist_Songs.ArtistID)
ON tblSong.SongID = tblArtist_Songs.SongID;

It almost never works as the recordsource for a form.

Once they realize it's not going to work, the next step is -- all too often -- to resort to VBA. When that happens, the neophyte decides to use a function to select values from controls on a form and insert them into the various tables using a Recordset, or perhaps a couple of dynamic SQL Statements.  Abandoning the benefits of the bound form in Access in favor of code sort of seems like an acceptable compromise.

Code Wadding

I call this approach to solving design problems "Code Wadding." You start with a small bit of code, and keep sticking new bits to it as you encounter new complications. Instead of resolving the basic table or interface design problems, you simply build a bigger wad of code around those problems.

When you have to write a wad of code to solve a basic design problem, you're probably going to regret it sooner or later. Code requires maintenance. Code requires error handling. Code requires additional interactions between the interface, the data, and the user. Code is really important, don't get me wrong. But applying an additional layer of code to all of the essential code in your MS Access Relational Database Application tends to make the code wad bigger, stickier and harder and harder to manage.

Basic Design Principles

In my opinion, the alternative to Code Wadding is adherence to basic design principles. Access became the most popular development tool for Relational Database Applications for many reasons. One of those is that it emphasizes and supports good design principles. It's easy to make mistakes, that's also true. However, the people who created Access were smart enough to make sure it's easy to build highly functional relational tables and interfaces based on good design principles.

Main Form - Sub Form Data Entry

Returning to the subject at hand, the proper interface design principle for Many-to-Many relationships is a main form/sub form design. The main form is bound to either of the two "one-side" tables. The sub form is bound to the junction table. One of the controls in the subform is a combo or list box which is bound to the foreign key for other "one-side" table.

The screenshot below illustrates the relevant characteristics of the main form/sub form design.
Main Form - Sub Form Design for Many-to-Many Relationships
  • The subform is bound to tblArtist_Songs. 
  • The main form is bound to tblArtist.
Although the Primary Key for tblArtist is visible in design view, it would normally be hidden when the form is displayed in normal view. It's an Access AutoNumber. Being a surrogate Primary Key, it's better NOT to show it to users.

In the subform, bound to tblArtist_Songs, the foreign key to SongID is bound to a combo box, as shown. The other foreign key for tblArtist is hidden in the subform. However, the subform control has been set up to use the ArtistID from the main form, called "Link Master Fields" in the property sheet, to populate the corresponding (hidden) control for the ArtistID in the subform. It's identified as "Link Child Fields" in the property sheet.

That's really all that is needed to make this work. Although you can add code to handle certain data entry errors or other tasks, it's not necessary to add "wads of code" to allow users to add, update, or delete records in the junction table bound to the subform.

In the sample database I created to illustrate this technique, I actually created two sets of forms. That allows users to start with artists and add recordings for existing songs, or to start with songs and add recordings for existing artists.

Rather than wasting time and energy trying to build a bigger wad of code, see if you can't implement a simple, basic interface design to do the job with a minimum of code.

Tuesday, December 24, 2019

Low Code Cascading Combo Boxes With TempVars

Cascading Combo Boxes are a staple of interfaces for Relational Database Applications. Cascading Combo Boxes are a series of 2 or more Combo Boxes in which each Combo Box is filtered according to a selection made in the previous Combo Box. 

For example, a vendor might use a series of combo boxes to find customers in a specific city by first selecting a State from a combo box bound to a Lookup table of States. That selection filters the City list in a combo box bound to a table of Cities. And that, in turn filters the list of customers to those whose address is found in the city selected in the City combo box.

Some time ago, I decided to see if I could simplify the process by using TempVars as the criteria for those combo boxes and forms. It turns out that there are a couple of advantages to using TempVars instead of more traditional approaches.

Dynamic SQL

One common approach is to dynamically re-write SQL Statements for "downstream" combo boxes to apply the filter selected in the "upstream" combo box. Something like this:

    strSQL = "SELECT CityName FROM tblCustomerAddress 
        WHERE StateName = '" & Me.cboSelectState & "'"
    Me.cboSelect.RowSource = strSQL

Form and Control References in Queries

Another approach is to incorporate a form control reference directly in the query, like this:

       SELECT CityName FROM tblCustomerAddress
        WHERE StateName = Forms!frmCustomers.cboSelectState

In both cases, as long as the form is open, the downstream, city, combo box will properly return the list of cities when it is requeried after a selection in the upstream, state, combo box.


I decided that I could do better. Instead of dynamic SQL or hard-coded form and control references, I could write queries that filter on TempVars. That gave me two advantages.

First, there's no need to fuss with writing and rewriting SQL dynamically. The rowsource of the downstream combo box, as well as the recordsource of the form, could be written as saved queries that never need to be modified at run time.

Second, because the TempVar can be set or modified as needed, the queries can be opened directly from the Navigation Pane whether the form is open or not. TempVars don't lose their values until some event in the Relational Database Application changes them. And that can make trouble-shooting just a little bit less fussy.

All or One

In addition to the flexibility and ease of use of TempVars, I found an additional tool to make Cascading Combo boxes even more useful. By wrapping the TempVars in an Immediate If  expression, I could select ALL records or only ONE record without having to do any additional coding. You can download a sample Access Relational Database Application using this method here:  Download of Cascading Combo Box From GPC Data.

Design View of Form's RecordSource Query with Iif()
Here are some screenshots of relevant components, starting with the query that populates the form's recordsource. 
SQL View of Form's RecordSource Query with Iif() 

Here's how it works. There are two possibilities. 

The value of TempVar can be 0 or it can be a positive, non-zero long integer. This is set in the AfterUpdate() event of the combo box on the form.

If the TempVar is 0, the Iif() expressions in the criteria select records where 0 = 0. In other words, ALL records will be returned.

If the TempVar is not 0, the Iif() expressions select records where the WorkID is equal to that TempVar value, which will be one record.

All we need to do is set the value of the TempVar in the AfterUpdate() Event and requery the form. 

Private Sub cboSelectWork_AfterUpdate()
    With Me
        TempVars.Add Name:="lngWorkID", Value:=Nz(.cboSelectWork, 0)
    End With
End Sub

One more trick makes it possible to return ALL records, if the user wants to see them, but we don't bog down the form by automatically doing so.

Here's the SQL from the combo box' rowsource:
UNION Query to Return ALL Records  or ONE Record
 Here's how it works. 
Cascading Combo Box Filtered to Work for One Custumer

One Customer, Darleve Sucknere,  has been selected in the upstream combo box for customers. This sets the TempVar that filters the downstream combo box for Work. It shows three projects done for that client, PLUS the option to select All Work for All Customers.

Download and Play with the Demo


The Cascading Combo Box with TempVars Demo  shows all of the features called out above, plus a few more enhancements you might like.

Let me know what you think.

Tuesday, December 17, 2019

Modifying Linked Tables

After two and a half decades of working with Access and answering questions in online forums, I am still surprised from time to time by questions about things I have long taken for granted. Here's a recent case in point.

The Question as Posed

First, the question, as posed, was a bit of a red herring (a lot of them are, as a matter of fact). The Original Poster (OP) wanted to know why his query seemed to "lose" new fields when he tried to add them. After a few back and forth responses with several other members trying to help, it finally turned out that the Access Relational Database Application in question was actually a split design, with a Back End for tables and a Front End for the interface elements including the query that was "losing fields". And from there it became clear what might be the underlying problem. The user was trying to add the new fields in the query and in the linked table in the front end.

The Solution Proposed

Once it became clear that the OP was trying to do this from within the Front End, the solution was much more straightforward. The new fields have to be added in the Back End and only then do they become available in the Front End.

I wish the solutions were all that simple although the detective work it took to get to it was a bit convoluted.

An Illustrated Example

As a follow-up, I decided to sketch out a quick illustration of the steps a successful table modification should follow in a typical Front End-Back End design. I used one of the basic sample data sets I keep for such purposes. It's based on Employees of an organization and the departments to which they are assigned.

Employees-Departments-Department Assignments

The relationship is many-to-many because each employee can be assigned to one or more departments and each department can have one or more employees. In this case, the relationship is intended to be sequential, rather than concurrent, in that employees would be assigned only to one department at a time. For that reason, the "fromDate" is included in the Primary Key for the EmployeeDepartment Junction table.

As a traditional Front End - Back End Access Relational Database Application, the forms are in one accdb and the tables in the other. The tables are linked, as can be seen in this image.
Linked Tables In Access FE, Identified by Arrow Icon

Employees and their assignments are managed through a traditional main form and subform design.
Main Form- Subform in Design View

Here's the same form in single form data entry view.
Main Form - Subform in Single View for Data Entry
After working with this Access Relational Database Application for a little while, the developer realized that it would be helpful to know when an employee leaves the organization. We want to add an Inactive Date to the Employee table.

However, not being experienced, the developer first tried to add the new field in the Front End, with this error.
Error Modifying Linked Table from Front End
A more experienced developer would immediately realize the problem and know how to solve it. Nonetheless, it does come up regularly, so I'm going to show you the next steps.

Open the Back End accdb with the tables. Open the Employee table in Design View.
Source Table in Back End accdb Open in Design View to Add Inactive Date
Now the appropriate field can be added and saved in the table.
InactiveDate Field Added in Source Table in Back End

Close the Back End accdb with the modified table in it. Reopen the Front End accdb. The new field should now be visible in the Linked Table. If it's not (and that's highly unlikely, of course), use the table relinker to refresh the link.
Refresh Links with Linked Table Manager
Now the new field can be included in the form's recordsource.
New InactiveDate Field Available for the Form's Recordsource
And a control for it can be added to the form.

New Field Available and Added to the Form.

Monday, December 16, 2019

Users Really DO Care About Your Interface

Last week I got a first-hand look at a user's reaction to a poorly designed interface. It made me smile.

I was in for a minor, routine medical procedure. The pre-op nurse was asking questions and entering my answers into the clinic's on-line medical records program. She noticed me staring at the screen and, perhaps thinking I was getting impatient (pardon the pun), felt she needed to apologize for how long it was taking. I assured her that I was mostly curious about the input process for professional reasons, having been a Relational Database Applicaton developer for many years. That prompted her to elaborate.

The system she was using required her to put in a couple of data points, then click a button or link to move to a different screen to add a few more data points, then move to a different screen for something else, and so on. She then explained that at her other job, they had a different system that allowed her to just scroll down as she entered data, without clicking and and waiting for a new screen to load. Much more efficient, at least in her opinion.

That told me a couple of things. First, she has joined the so-called Gig Economy and has, for better or worse, a variety of work environments to compare. Probably, she's not the only one doing that these days.

But more importantly, it told me that interface design is a big deal. I doubt that this particular nurse would give up a particular job because of it, but I would bet that if it came down to a choice between the two positions she holds, she is very much aware of, and concerned about, the usability of the tools available at the two.

Tuesday, December 10, 2019

Multi-Purpose Forms in an Access Relational Database Application

Microsoft Access is very flexible development tool. Seasoned developers know this, and take advantage of that flexibility in different ways. For example, different interface objects can be used for two or more purposes. A recent question at UtterAccess gave me an opportunity to create a small demo to illustrate how re-use of objects works.

In this demo Access Relational Database Application, I used one of the arguments for the DoCmd.OpenForm action to change the Data Mode for a single form.
Here's the full line of code, taken from two different procedures: 

    DoCmd.OpenForm FormName:="frmHousehold", View:=acNormal, DataMode:=acFormAdd

which runs from the Click Event of one Command Button. 

    DoCmd.OpenForm FormName:="frmHousehold", View:=acNormal, DataMode:=acFormEdit

which runs from the Click Event of the other Command Button. 

Two Command Buttons Open One Form in Two Different Data Modes

This is a very simple illustration of the re-use of objects. Instead of creating two different objects--add and edit forms in this case--to do two very similar tasks, we re-use the same object but vary the way it is used. Because adding records to a table, and editing records in that same table are almost identical tasks; it's obvious that we can simplify the Access Relational Database Application this way.

This is a simple example of a much broader set of design principles and practices. If you want to learn more, here's an excellent YouTube video by Phillip Steifel.