Dynamic Elastic search query in c# NEST

Question

Started working on NEST api for elastic search recently, got stuck on following query, the data.e would be dynamically populated using the input from client in the HttpGet, ex: user sends eventA,eventB,eventC then we would add in the should part:

GET events/_search
{
  "_source": false, 
  "query": {
    "bool": {
      "must": [
        {"range": {
          "timestamp": {
            "gte": 1604684158527,
            "lte": 1604684958731
            }
        }},
        {"nested": {
          "path": "data",
          "query": {
            "bool": {
              "should": [
                {"match": {
                   "data.e": "eventA"
                }},
                {"match": {
                  "data.e": "eventB"
                }},
                {"match": {
                   "data.e": "eventC"
                }},
              ]
            }
            },
          "inner_hits": {} 
        }}
      ]
    }
  }
}

Following is what I came up with till now:

var graphDataSearch = _esClient.Search<Events>(s => s
                .Source(src => src
                    .Includes(i => i
                        .Field("timestamp")
                        )
                 )
                .Query(q => q
                    .Bool(b => b
                        .Must(m => m
                                .Range(r => r
                                    .Field("timestamp")
                                    .GreaterThanOrEquals(startTime)
                                    .LessThanOrEquals(stopTime)
                                    ),
                                m => m
                                .Nested(n => n
                                    .Path("data")
                                    .Query(q => q
                                        .Bool(bo => bo
                                            .Should(
                                            // what to add here?
                                    )
                                    )
                                )
                        )
                    )
                ));

Can someone please help how to build the should part dynamically based on what input the user sends?

Thanks.

Sai Gummaluri · Accepted Answer · 2020-11-21 04:32:00Z

3

You can replace the nested query in the above snippet as shown below

// You may modify the parameters of this method as per your needs to reflect user input
// Field can be hardcoded as shown here or can be fetched from Event type as below
// m.Field(f => f.Data.e)

public static QueryContainer Blah(params string[] param)
{
    return new QueryContainerDescriptor<Events>().Bool(
        b => b.Should(
            s => s.Match(m => m.Field("field1").Query(param[0])),
            s => s.Match(m => m.Field("field2").Query(param[1])),
            s => s.Match(m => m.Field("field3").Query(param[2]))));
}

What we are essentially doing here is we are returning a QueryContainer object that will be passed to the nested query

.Query(q => Blah(<your parameters>))

The same can be done by adding this inline without a separate method. You may choose which ever route you perfer. However, in general, having a method of its own increases the readability and keeps things cleaner.

You can read more about Match usage here

Edit:

Since you want to dynamically add the match queries inside this, below is a way you can do it.

private static QueryContainer[] InnerBlah(string field, string[] param)
{
    QueryContainer orQuery = null;
    List<QueryContainer> queryContainerList = new List<QueryContainer>();
    foreach (var item in param)
    {
        orQuery = new MatchQuery() {Field = field, Query = item};
        queryContainerList.Add(orQuery);
    }
    return queryContainerList.ToArray();
}

Now, call this method from inside of the above method as shown below

public static QueryContainer Blah(params string[] param)
{
    return new QueryContainerDescriptor<Events>().Bool(
        b => b.Should(
            InnerBlah("field", param)));
}

edited Nov 21, 2020 at 4:32

answered Nov 19, 2020 at 7:40

Sai Gummaluri

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6 Comments

Ghanendra Over a year ago

The part inside the should(), needs to be dynamically created, user could send 4 events or 5 events, so we have to match those too, the solution you posted is hardcoded for 3 type of params only which I showed as example.

Sai Gummaluri Over a year ago

You can loop over the items that are sent across and generate the inner match query inside of should. Will edit the answer to provide pointers on how to do it

Sai Gummaluri Over a year ago

@Ghanendra - Added the dynamic generation logic for multiple match queries

Ghanendra Over a year ago

Thanks for the help! I had to modify your code a bit to the following

private QueryContainer[] InnerBlah(string field, List<string> param)         {             QueryContainer orQuery = null;             List<QueryContainer> lq = new List<QueryContainer>();             foreach (string item in param)             {                 orQuery = new MatchQuery() { Field = field, Query = item };                 lq.Add(orQuery);             }             return lq.ToArray();         }

, Otherwise it was creating multiple should[bool( elements in the Request json

Sai Gummaluri Over a year ago

@Ghanendra - Ah! True that. I have amended the answer to reflect the change. Cheers!

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