How to use POCOs with Fields in Elasticsearch.Net (NEST)?

Question

How to I get a strongly-typed list of objects back when doing a search that uses Fields()? For example:

var searchResult = client.Search<Person>(s => s
    .Fields("title", "name")
    .Query(q => q.Match(...etc...)
    .Highlight(...etc...)
);

It seems like the generic type parameter is useless when .Fields() is used because the Hits that are returned have a null .Source property.

(I'm hoping there's a way to do it without having to manually map the search results back to my original Person POCO.)

Answer 1

When you use fields parameter in your query, elasticsearch returns specified fields in fields section of response.

{
"took" : 36,
"timed_out" : false,
"_shards" : {
    "total" : 2,
    "successful" : 2,
    "failed" : 0
},
"hits" : {
    "total" : 18,
    "max_score" : 1.0,
    "hits" : [{
            "_index" : "nest_test_data-2672",
            "_type" : "elasticsearchprojects",
            "_id" : "1",
            "_score" : 1.0,
            "fields" : {
                "pingIP" : ["127.0.0.1"],
                "country" : ["Faroese"],
                "intValues" : [1464623485],
                "locScriptField" : [0],
                "stupidIntIWantAsLong" : [0],
                "floatValues" : [84.96025, 95.19422],
                "floatValue" : [31.93136],
                "myAttachment" : [""],
                "doubleValue" : [31.931359384176954],
                "suggest" : [""],
                "version" : [""],
                "content" : ["Bacon ipsum dolor sit amet tail non prosciutto shankle turducken, officia bresaola aute filet mignon pork belly do ex tenderloin. Ut laboris quis spare ribs est prosciutto, non short ribs voluptate fugiat. Adipisicing ex ad jowl short ribs corned beef. Commodo cillum aute, sint dolore ribeye ham hock bresaola id jowl ut. Velit mollit tenderloin non, biltong officia et venison irure chuck filet mignon. Meatloaf veniam sausage prosciutto qui cow. Spare ribs non bresaola, in venison sint short loin deserunt magna laborum pork loin cillum."],
                "longValue" : [-7046341211867792384],
                "myBinaryField" : [""],
                "name" : ["pyelasticsearch"],
                "boolValue" : [false],
                "id" : [1],
                "startedOn" : ["1994-02-28T12:24:26.9977119+01:00"]
            }
        }
    ]
}
}

You can retrieve them from searchResult.FieldSelections or searchResult.Hits[...].Fields.

In your case Source filtering should be much more convenient.

        [Test]
    public void MatchAllShortcut()
    {
        var results = this.Client.Search<ElasticsearchProject>(s => s
            .From(0)
            .Size(10)
            .Source(source=>source.Include(f => f.Id, f => f.Country))
            .SortAscending(f => f.LOC)
            .SortDescending(f => f.Country)
            .MatchAll()
        );

        Assert.NotNull(results);
        Assert.True(results.IsValid);

        Assert.NotNull(results.Hits);
        Assert.GreaterOrEqual(results.Hits.Count(), 10);
        Assert.True(results.Hits.All(h => !string.IsNullOrEmpty(h.Source.Country)));

        Assert.NotNull(results.Documents);
        Assert.GreaterOrEqual(results.Documents.Count(), 10);
        Assert.True(results.Documents.All(d => !string.IsNullOrEmpty(d.Country)));
    }