Elasticsearch：有条件地对2个字段进行排序，1替换另一个字段（如果存在）

Question

Without scripting, I need to sort records based on rating. The system-rating exists for all records, but a user-rating may or may not exist. If a user-rating does exist I want to use that value in the sort instead of the system-rating, for that particular record and only for that record.

Tried looking into the missing setting but it only allows _first , _last or a custom value (that will be used for missing docs as the sort value):

{
    "sort" : [
        { "user_rating" : {"missing" : "_last"} },
    ],
    "query" : {
        "term" : { "meal" : "cabbage" }
    }
}

...but is there a way to specify the custom value should be system_rating when user_rating is missing?

I can do the following:

query_hash[:sort] = []
if user_rating.exist?
  query_hash[:sort] << {
    "user_rating" => {
      "order": sort_direction,
      "unmapped_type": "long",
      "missing": "_last",
    }
  }
end
query_hash[:sort] << {
  "system_rating" => {
    "order": sort_direction,
    "unmapped_type": "long",
  }
}

...but that will always sort user rated records on top regardless of the user_rating value.

I know that scripting will allow me to do it but we cannot use scripting. Is it possible?

Answer 1

唯一的方法是在索引时编写脚本或构建自定义字段，该字段将包含已经构建的排序值。