subquerysanitygroqarray-comparison

How to compare arrays in GROQ

I have a blog with sanity CMS and I want to request related posts depending on corresponding tags from the current post which means I have to compare two arrays of tags.

My tags are described in post schema this way:

{
  name: 'tags',
  title: 'Tags',
  type: 'array',
  of: [{type: 'string'}],
  options: {
    layout: 'tags'
  }
},

I went with the following GROQ query which is a good start I guess but obviously it doesn't work:

*[_type == "post" && slug.current == $slug][0] {
  title,
  tags,
  "sameTags": *[_type == "post" && slug.current != $slug && count(tags in ^.tags) > 0]
}

What I would translate my query to is: "I want to get related posts which have a different slug and that own at least one tag also owned by the current post"

Solution

  • The count trick should work, but since you are comparing multiple tags against multiple tags, you need to iterate over them:

    count(tags[@ in ^.^.tags]) > 0

    In other words, it filters the tags by whether each tag appears in the other list. The additional ^. should be needed here, as the filter introduces a new scope.