How do I use a parameter in an #if value in mediawiki?

Question

I'm trying to create a mediawiki template:

|-
| {{{name}}}{{#if:{{{ref|}}}|<ref>{{{ref}}}</ref>|}}{{#if:{{{ndb|}}}|<ref>https://ndb.nal.usda.gov/ndb/foods/show/{{{ndb}}}</ref>|}} || {{{size|--}}} || {{{carbs|--}}} || {{{sugar|--}}} || {{{fiber|--}}} || {{{fat|--}}} || {{{protein|--}}}

Most of it works OK but if I pass a ref or a ndb parameter, the #if doesn't work properly I get

<ref>{{{ref}}}</ref>

or

<ref>https://ndb.nal.usda.gov/ndb/foods/show/{{{ndb}}}</ref>

I don't get what I would expect:

<ref>http://the.passed.value/</ref>

or

<ref>https://ndb.nal.usda.gov/ndb/foods/show/passed_value</ref>

Answer 1

#if doesn't seem to be the cause of the issue. The reason is that <ref> is not processed in the order you're expecting. You need #tag to generate a parser or extension tag at a later template processing stage:

Template:Google source code:

<includeonly><!--
-->{{#if: {{{ref|}}}
   | {{#tag: ref |{{{ref}}}}}
   }}<!--
-->{{#if: {{{q|}}}
   | {{#tag: ref |[https://google.com/search?q={{#urlencode:{{{q}}}}} Google: {{{q}}}]}}
   }}<!--
--></includeonly>

Page source code:

{{Google
| ref = http://google.com/search?q=foo+bar
| q = foo bar
}}

<references/>

Page output:

[1][2]

1. ↑ http://google.com/search?q=foo+bar
2. ↑ Google: foo bar