GraphQL Search facetOn Parameter

Question

I'm trying to use the Sitecore GraphQL search function that takes in the "facetOn" parameter. Unfortunately I'm not having much luck with the results, and I suspect it's because I'm doing something wrong and don't know where to look for the documentation. So I have a Field called "Category" and I want to facet on that when I search because I imagine it will essentially give me a count of different "Category" value occurrences. But the below is not working.

query {
  search(rootItem: "92B4F8E7-6324-4C01-B873-7FDC992EDDEE" facetOn:["_category"] ) {
    results {
      totalCount
      items {
        item {
          name
          _category: field(name: "Category") {
            value
          }
        }
      }
    }

    facets {

      name
      values {
        item {
          id

        }
        value
      }

    }
  }
}

Answer 1

Your query looks good, I test it on Sitecore 9.1, SOLR with a Text field, that work with this adjustment. It is now facetOn "_category" looks like because the field(name: "Category") your field is named "Category" so use

search(rootItem: "92B4F8E7-6324-4C01-B873-7FDC992EDDEE" facetOn:["Category"] )

It is not giving a count per facet. you can do that by adding the count to the facets

facets {
      name
      values {
        count
        item {
          id
        }
        value
      }
}

Note, this is working on SOLR, for Azure Search there are some limitations, facet on an list is an issue, ARGUMENT_OUT_OF_RANGE

Below is a working example on the out of the box Title field from the sample item. (note item in facet is null, because result is a string not a reference)

query {
  search(rootItem: "/sitecore/content/home" facetOn:["Title"]  ) {
    results {
      totalCount
      items {
        item {
          name
          _TitleField: field(name: "Title") {
            value
          }
        }
      }
    }

    facets {
      name
      values {
        count
        item {
          id
        }
        value
      }

    }
  }
}

One thing to mention, in my returning facet name it is lowercased so Category returns as category, also a GUID returned as uppercase without dash, if you want to search on that do first a to lowercase.