Many programs assign their beneficiaries externally-facing IDs. Using a combination of custom user data and a counter you can assign unique IDs to your beneficiaries. Since CommCare works offline you must create a portion of the ID that is based on the user case, since each user can be working offline simultaneously.
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Note on Case IDs versus Unique IDs
CommCare assigns every case a globally unique case ID that is a 36-character long alphanumeric string. You should always use the case ID to link your data on the backend. These instructions detail how to create an easily readable user-facing ID for beneficiaries. This should not be used to link data on the backend or for any data analysis.
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Generating a Unique ID
Step 1: Create a property in custom user data
Create Custom User Data property for each mobile user called "prefix"
Assign each user a prefix value, for example, 10, 11, 12, 13, 14 and so on. In order to determine your prefixes, you need to think about how many beneficiaries you expect each mobile user to register. In this example, we do not expect the user to register more than 10,000 beneficiaries, ever, and our prefixes and suffixes match that.
You can assign this prefix when you add the mobile users individually, or in bulk.
Notably, this prefix can also be a letter or a code, it does not have to be numeric.
Step 2: Create a counter in your registration form
In your registration form, implement a counter as explained here: https://dimagi.atlassian.net/wiki/spaces/commcarepublic/pages/2143946181/Calculations+in+Hidden+Values#Incrementing-a-counter
Save this property to the user case. This will increment one time every time the user opens the form. In our example, we've saved this user case property as child_count.
Step 3: Create a hidden value to generate the unique ID
Finally, in your registration form, create a hidden value called beneficiary_id that joins together the custom user property created in step 1 with the counter created in step 2 using the https://dimagi.atlassian.net/wiki/spaces/commcarepublic/pages/2143946181/Calculations+in+Hidden+Values#Join-two-values-(%22concatenate%22)
Since the counter will generate a number starting at 1 and constantly increment, you'll also want to make sure that you prepend 0's to the counter’s output so that all IDs are the exact same length. See the example below for more information.
Save this hidden value as a case property to the case you're tracking (not to the user case)
Example
Let's look at an example of how this would work in an app.
In step 1, my user case property is called prefix.
In step 2, the counter that I made is saved as the property child_count.
So finally, in step 3, the calculation that I would put into my beneficiary_id calculate condition box would be:
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