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Strange Equation Behavior in a Knack Database App



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Hey folks, Dave Parrish here with Knack Builders. In today's post, I want to dive into an interesting challenge I encountered while working with equations in one of my Knack database apps. It’s a bit technical, but bear with me, and I promise you'll find it enlightening. Let’s jump right in!


Encountering the Problem

I recently stumbled upon a strange behavior in an equation. It wasn't recognizing the value that existed in the field itself. This issue was tied to finding the latest or earliest date in a series using the min or max functions. Here’s a quick overview of the problem:

  • Dates need to be converted into numbers to use the min or max functions effectively.

  • After running these functions, the resulting number needs to be converted back into a date.

  • This conversion process involves Unix time, where everything starts from January 1, 1970. The number represents the days since this epoch date.


However, despite setting everything up correctly, the equation was returning 1970, meaning it was either viewing the value as zero, null, or something else. It should have been recognizing the number of days since 1970 and giving me the right date.


Diving into the Use Case

Let me provide some context with a real-world use case from my Knack app. I'm building an app for a company that helps other companies place their employees on non-profit boards. Here's how it works:

  1. Collecting Information: The company gathers information about individuals who want to be on a board.

  2. Matching Process: Based on their interests, these individuals are presented with various boards they could join.

  3. Tracking Milestones: We collect several dates to report back to the client, including the first time an individual was introduced to a board.

One of the critical dates we need is the first introduction date. Using the min function should automate this process by selecting the earliest date.


The Core of the Issue

Here's where things get tricky. The min function should look at the dates, converted to numbers, and return the earliest date. However, when converting this number back into a date, the equation wasn't working correctly, returning 1970 instead.

To troubleshoot, I created a number field to turn the problematic value into an actual number. I then applied a condition to make this value the minimum date returned by the min function. By adding some "field acrobatics," I transformed the number into a date correctly.


Solving the Mystery

After some experimenting, I found a straightforward fix. I noticed that when performing a simple equation, like adding one to the number, the original number was recognized correctly. However, when trying to convert it into a date, it failed in Knack.

Here's what I did:

  1. Created a Number Field: I converted the value into a number field.

  2. Applied a Condition: I set the value as the minimum date returned by the min function.

  3. Transformed the Number: I converted this value into a date, which then gave me the proper number of days from January 1, 1970.

This approach worked seamlessly, and the equation returned the correct date. However, the mystery of why the initial equation didn’t work still puzzles me.


Seeking Insights

If anyone has insights into why this issue occurs with your Knack apps, I’d love to hear from you. Understanding the root cause could help prevent similar problems in the future.

Thank you for following along on this technical journey. Remember to like and subscribe to my YouTube channel for more content like this. Until next time!

That’s all I got. If you have any thoughts or experiences with similar issues, please share them in the comments. Your feedback is invaluable!


Click here for my Unix Time blog post.

Click here for my Finding a Date blog post.


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