Question 39994 in PHP Question posted in
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Only allow year/month/day or year/month or year only? – PHP

I need to only allow:

  • a year
  • a year and a month
  • a year and a month and a day

I should not allow:

  • anything without a year
  • a month by itself
  • a day by itself
  • a month and day
  • a year and a day

I have written

if ($year && (($month && $day) || ($month && ! $day) || (! $month && ! $day)))

But it seems rather lengthy – is there a more concise way?

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2

Answers


  1. 0

    Unit testing helps with clearing up any uncertainly.

    My interpretation of your input data is that your non-null values can never be zero. The condition statement below will be making truthy/falsey checks — this means that any encountered 0 values will be evaluated as falsey.

    Code: (Demo)

    if ($year && ($month || !$day)) {
    • The $year value is required.
    • If the $month also exists, then it’s still good.
    • If the $month does not exists, then $day must not as well.
      In other words, the !$day check is only executed if $month is not truthy.
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  2. 0

    You can use a KV diagram to find the expressions, which can be combined with || and simplify them. The KV diagram looks like this:

       |  Y | !Y |
---+----+----+---
   |  1 |  0 |  D
 M +----+----+---
   |  1 |  0 | 
---+----+----+ !D
   |  1 |  0 | 
!M +----+----+---
   |  0 |  0 |  D
---+----+----+---

    Which results in two sub expressions $year && $month and $year && !$day like this:

    ($year && $month) || ($year && !&day)

    And this can be simplified to:

    $year && ($month || !$day)
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