Search users with elasticsearch

The problem with your search is that it does not specify a field to perform the match query on; the value to perform a match with is specified but not the field.

In this scenario, NEST's conditionless query logic (note: this is old documentation, but conditionless queries apply to newer versions of NEST) kicks in and because field does not have a value, the match query is not emitted as part of the search request. The request ends up looking like

POST http://localhost:9200/users/userinfo/_search 
{
    "from":0,
    "size":10
}

with the document with UserNr 1 returned.

To fix this, you just need to specify the field name. Here's a complete example to demonstrate

void Main()
{
    var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
    var connectionSettings = new ConnectionSettings(pool)
        // Disabling direct streaming and logging out requests and responses
        // is useful during development, but may not want to do this
        // in production as it has performance implications.
        // Used here to write out requests and responses.
        .DisableDirectStreaming()
        .OnRequestCompleted(response =>
            {
                // log out the request
                if (response.RequestBodyInBytes != null)
                {
                    Console.WriteLine(
                        $"{response.HttpMethod} {response.Uri} \n" +
                        $"{Encoding.UTF8.GetString(response.RequestBodyInBytes)}");
                }
                else
                {
                    Console.WriteLine($"{response.HttpMethod} {response.Uri}");
                }

                // log out the response
                if (response.ResponseBodyInBytes != null)
                {
                    Console.WriteLine($"Status: {response.HttpStatusCode}\n" +
                             $"{Encoding.UTF8.GetString(response.ResponseBodyInBytes)}\n" +
                             $"{new string('-', 30)}\n");
                }
                else
                {
                    Console.WriteLine($"Status: {response.HttpStatusCode}\n" +
                             $"{new string('-', 30)}\n");
                }
            })
            .DefaultIndex("users");

    var client = new ElasticClient(connectionSettings);

    var ui = new UserInfo { UserName = "Andy", Name = "", UserNr = 1 };

    if (!client.IndexExists("users").Exists)
    {
        client.CreateIndex("users");
    }

    // can use index
    client.Index(ui, descriptor => descriptor.Refresh());

    var pageSize = 10;
    var currentPage = 1;
    var name = "gujjghjhgj";

    var searchResponse = client.Search<UserInfo>(s => s
        .Index("users")
        .Query(q => q
            .Match(m => m
                // specify the field 
                .Field(f => f.UserName)
                .Query(name)                
            )
        )
        .Size(pageSize)
        .From((currentPage - 1) * pageSize)
    );

    var total = searchResponse.Total; 
    var docs = searchResponse.Documents.ToList();
}

[Serializable, ElasticsearchType(IdProperty = "UserNr")]
public class UserInfo
{
    public string UserName { get; set; }
    public string Name { get; set; }
    public string Avatar { get; set; }
    public int UserNr { get; set; }
}