Grouping & Filtering #1 – Cascading combo boxes example

[isladogs]

This is intended as the first in a series of examples showing different ways of filtering and grouping data in Access

This example focuses on the use of cascading combo boxes. This method is particularly useful where you have a very large dataset that would be impossibly slow to search using a single combo box or listbox

For example, in my UK Postal Address Finder app, I have a table of 2.6 million postcodes. I have mentioned this example before in various threads.
For example: https://www.access-programmers.co.uk/forums/showpost.php?p=1580504&postcount=37

For info, UK postcodes have 7 or 8 characters including a space
- Area e.g. HA
- District e.g. HA3
- Sector e.g. HA3 0
- Zone e.g. HA3 0S
- Postcode e.g. HA3 0SN
For anyone interested, additional info is provided in the attached PDF file

NOTE: All the above are official UK postcode terminology except zone (added here to assist with searching sectors)

The normal postcode entry is a textbox. A postcode builder is available when you aren't sure what postcode to enter.

Searching a dataset of this size is obviously impossible using a single combo box. To make it manageable, the search is broken down using 5 cascading combos. The contents of each combo are dependant on the choices made in the previous combo

Each combo is based on a separate table filtered on the previous selection which makes it very fast.
In addition, all fields used in the combo searches are indexed. This increases the database size BUT makes a dramatic difference to the search time needed

The attached example is a cut down version of the postcode builder to make the file small enough to upload here.
It only has data for two of the 125 postcode areas in the UK - Bristol (BS) & Kirkwall (KW). Inactive postcodes have been removed from the list
This reduces the total number of postcodes to around 28500 instead of the full data set of 2.6 million

It also contains an example postcode map. Please keep this in the same folder as the database.

Click the OK button to start using the postcode builder
A dropdown box appears with a list of postcode areas. Select an area from the list

Further dropdown lists appear in turn until you have selected a full postcode

In the full app, a Google static map centred on the postcode geo-coordinates is automatically downloaded.
The attached just uses the same example map for each postcode

Another good example of the use of cascading combo boxes is provided on the FMS website: http://www.fmsinc.com/microsoftaccess/forms/combo-boxes/cascading.html

It would be helpful if others could provide links to good examples of cascading combos

 

[Dangerous]

This is intended as the first in a series of examples showing different ways of filtering and grouping data in Access

Thanks for your reply, Your postcode builder works perfectly but having looked at the AfterUpdate event code I've no idea how to convert it to my need as I don't understand some of it.

I've also looked at the FMS example (have looked at it before but not actually downloaded it till today) and, for me, selecting 'Animal' in the 'Kingdom' dropdown then opening the 'Phylum@ dropdown it is blank (as it is for other entries in 'Kindom' if selected despite there being 3 'Phylum' names shown with the 'KingdonID' of 'Animal'. The remainder of the dropdowns don't limit the list to data in the previous dropdown.

For now 2 levels of cascade will do me & if I get it working I could, if need be, develop it further but at the moment I'm stuck.

 

[isladogs]

Hi
You posted to a moderated area rather than your own thread.
The principle is the same whether you have 2 cascading combos or more than that.
Happy to explain if you have a specific question about my example.
If so, please DON'T REPLY HERE -send me a PM instead

I have to admit I've only looked at the example on the FMS site and not actually tried it.
I'm surprised they would publish something that doesn't work properly as it's a very good site.
Can suggest you inform FMS about those issues. They may wish to fix them