Search document with empty array field, on OpenSearch

Question

I have a set of documents and I want to search for the document which elements/objects has empty array field.

I have tried with the below query , need check for documents where `expenseTypes` field exists but is empty

{
  "bool" : {
    "must" : [
      {
        "bool" : {
          "should" : [
            {
              "bool" : {
                "must" : [
                  {
                    "exists" : {
                      "field" : "expenseTypes",
                      "boost" : 1.0
                    }
                  },
                  {
                    "bool" : {
                      "must" : [
                        {
                          "term" : {
                            "expenseTypes" : {
                              "value" : "",
                              "boost" : 1.0
                            }
                          }
                        }
                      ],
                      "adjust_pure_negative" : true,
                      "boost" : 1.0
                    }
                  }
                ],
                "adjust_pure_negative" : true,
                "boost" : 1.0
              }
            }
          ],
          "adjust_pure_negative" : true,
          "boost" : 1.0
        }
      }
    ],
    "adjust_pure_negative" : true,
    "boost" : 1.0
  }
}

which should return the documents which has expenseTypes empty like below

{
        "id": "123466",
        "expenseTypes": []
       
    }```

Answer 1

I tried with below query which is matches the empty array

{
  "bool" : {
    "must" : [
      {
        "bool" : {
          "should" : [
            {
              "bool" : {
                "must_not" : [
                  {
                    "exists" : {
                      "field" : "expenseTypes",
                      "boost" : 1.0
                    }
                  }
                ],
                "adjust_pure_negative" : true,
                "boost" : 1.0
              }
            }
          ],
          "adjust_pure_negative" : true,
          "boost" : 1.0
        }
      }
    ],
    "adjust_pure_negative" : true,
    "boost" : 1.0
  }
}

Answer 2

You need to use a combination of exists and term queries within a bool query

• exists query ensures that expenseTypes exists
• term query checks if expenseTypes is an empty array

{
  "query": {
    "bool": {
      "must": [
        {
          "exists": {
            "field": "expenseTypes"
          }
        },
        {
          "term": {
            "expenseTypes": {
              "value": []
            }
          }
        }
      ]
    }
  }
}