How to merge multiple 'relatedTo' queries via query parameters

Question

I'm trying to augment a Commerce query with additional parameters like so, but I can't get 'colour' and 'range' working together. Clearly my and/relatedTo syntax is wrong but how exactly?

  {% set colour = craft.app.request.getQueryParam('colour') ?? null %}
  {% set range = craft.app.request.getQueryParam('range') ?? null %}

  {% set query = {
    type: 'fabric',
    limit: 999,
    orderBy: 'defaultSku asc'
  } %}

  {% set query = colour is defined ? query|merge({ relatedTo: ['and', { targetElement: craft.categories.slug(colour) }]}) : query %}

  {% set query = range is defined ? query|merge({ relatedTo: ['and', { targetElement: craft.categories.slug(range) }]}) : query %}

  {% set swatches = craft.products(query).all() %}
  {% for swatch in swatches %}

(Also need to add further queries params for texture etc which are also related to categories)

Answer 1

I figured it out with help from https://craftcms.stackexchange.com/a/5339/7356

This could probably be further refined but...

  {# Get query parameters from URL #}
  {% set colour = craft.app.request.getQueryParam('colour') ?? null %}
  {% set range = craft.app.request.getQueryParam('range') ?? null %}
  {% set texture = craft.app.request.getQueryParam('texture') ?? null %}

  {# Tee up the product query #}
  {% set queryParams = [colour, range, texture] %}
  {% set hasValidQueryParams = false %}
  {% set relationParam = ['and'] %}
  {% set query = {
    type: 'fabric',
    limit: 999,
    orderBy: 'defaultSku asc'
  } %}

  {# Store any valid query parameters #}
  {% for param in queryParams %}
    {% if param != null %}
      {% set hasValidQueryParams = true %}
      {% set relationParam = relationParam|merge([{targetElement: craft.categories.slug(param) }]) %}
    {% endif %}
  {% endfor %}

  {# Merge query parameters into the main product query  #}
  {% if hasValidQueryParams %}
    {% set query = query|merge({relatedTo: relationParam}) %}
  {% endif %}

  {# Display the result  #}
  {% set swatches = craft.products(query).all() %}
  {% for swatch in swatches %}
    {% include 'range/_fabric_swatch' with { 'visible': true } %}
  {% endfor %}