Elastic / Nest (C#) - Get max Id in index-CodePudding

I have an entity stored inside an Elastic Index, one of his fields is an Id (int).

I'm currently using this code to retrieve the data:

var searchRequest = new SearchRequest<MyEntity>(indexName)
{
    Size = 1,
    Query = new MatchAllQuery(),
    Sort = new List<ISort>()
    {
        new FieldSort(){ Field = "_id", Order = SortOrder.Descending }
    }
};

var result = await _elasticClient.SearchAsync<MyEntity>(searchRequest);
var highestId = result.Documents.First().Id;

This code does not return the max Id but it returns the id "999999". What I think its happening is that "_id" in search request it's not the Id inside my entity. What is the correct way to query that value instead?

Edit: I tried of course using "id" (or Id) in the code up above but I get an excpetion

Elasticsearch.Net.UnexpectedElasticsearchClientException : expected:'true | false', actual:'"true"', at offset:639

Also I tried this but I get an id that its even lower that the previous one:


var response = await _elasticClient.SearchAsync<MyEntity>(s => s
                    .Index(indexName)
                    .Size(1)
                    .Aggregations(a => 
                        a.Max("max_id", x => x.Field("id"))
                    )

CodePudding user response：

if you use id your entity try this:

GET my-index-000001/_search
{
  "size": 0,
  "aggs": {
    "max_id": {
      "max": {
        "field": "id"
      }
    }
  }
}

CodePudding user response：

In the end here's the solution:

After the response from @rabbitbr I was able to get this request:

var response = await _elasticClient.SearchAsync<MyEntity>(s => s
                    .Index(indexName)
                    .Take(1)
                    .Aggregations(aggr =>
                        aggr.Max("get_max_id", max =>
                            max.Field(field => field.Id)
                            )
                    )
                );

var highestId = result.Documents.First().Id;

Here my error was NOT the query but how I collected the result: the correct way to get the value of "highestId" is to get from the response the field "Aggregations", then using .Max(aggregationName)

var aggregationName = "get_max_id";
var response = await _elasticClient.SearchAsync<MyEntity>(s => s
                    .Index(indexName)
                    .Take(0)
                    .Aggregations(aggr =>
                        aggr.Max(aggregationName , max =>
                            max.Field(field => field.Id)
                            )
                    )
                );

var highestId = response.Aggregations.Max(aggregationName).Value;