Copy_to in Nest Attributes

[mjgasior (Michał Gąsior)]

Is it possible to use copy_to in Nest attributes? I know, there is an option to use the Fluent Mapping (but the CopyTo doesn't work with string) instead of Attribute Mapping. And if I do make a "copy_to", do I have to add another field to my Mapping class as a placeholder? These are my mappings:

[ElasticsearchType(Name = "project")]
public class Project
{
	public Guid Id { get; set; }
	public bool IsOpen { get; set; }
	public bool IsDeployed { get; set; }
            
    [Text(Analyzer = "substring_analyzer")]
	public string ExternalCode { get; set; }
	public Owner Owner { get; set; }
}

public class Owner
{
	public string FirstName { get; set; }
	public string LastName { get; set; }
}

And initialization:

client.CreateIndex(INDEX_NAME, descriptor => descriptor
	.Mappings(ms => ms
		.Map<Project>(m => m.AutoMap())
	)
	.Settings(s => s
		.Analysis(a => a
			.Analyzers(analyzer => analyzer
				.Custom("substring_analyzer", analyzerDescriptor => analyzerDescriptor
					.Tokenizer("keyword")
					.Filters("lowercase", "substring")
				)
			)
			.TokenFilters(tf => tf
				.NGram("substring", filterDescriptor => filterDescriptor
					.MinGram(1)
					.MaxGram(9)
				)
			)
		)
	)
);

I'd like to use the copy_to option on Owner.FirstName, Owner.LastName and the ExternalCode fields, and than add the NGram tokenizer to the whole stuff.

[forloop (Russ Cam)]

You can't specify copy_to fields with attribute mapping because multiple fields can be specified, which are represented with the Fields type, and attribute parameters are restricted to constant values, so it's not possible to assign an instance of Fields within an [Attribute] declaration.

You can define copy_to fields with fluent mapping though. Since the original _source field is not modified, you don't need to add another property to your C# POCO for a copy_to field. Here's an example

client.CreateIndex("my-index", descriptor => descriptor
	.Mappings(ms => ms
		.Map<Project>(m => m
			.AutoMap()
			.Properties(p => p
				.Text(t => t
					.Name(n => n.ExternalCode)
					.Fields(f => f
						.Keyword(k => k
							.Name("keyword")
							.IgnoreAbove(256)
						)
					)
					.CopyTo(c => c
						.Field("another_field")
					)
				)
				.Object<Owner>(o => o
					.Name(n => n.Owner)
					.AutoMap()
					.Properties(pp => pp
						.Text(t => t
							.Name(n => n.FirstName)
							.Fields(f => f
								.Keyword(k => k
									.Name("keyword")
									.IgnoreAbove(256)
								)
							)
							.CopyTo(c => c
								.Field("another_field")
							)
						)
						.Text(t => t
							.Name(n => n.LastName)
							.Fields(f => f
								.Keyword(k => k
									.Name("keyword")
									.IgnoreAbove(256)
								)
							)
							.CopyTo(c => c
								.Field("another_field")
							)
						)
					)
				)
			)
		)
	)
	.Settings(s => s
		.Analysis(a => a
			.Analyzers(analyzer => analyzer
				.Custom("substring_analyzer", analyzerDescriptor => analyzerDescriptor
					.Tokenizer("keyword")
					.Filters("lowercase", "substring")
				)
			)
			.TokenFilters(tf => tf
				.NGram("substring", filterDescriptor => filterDescriptor
					.MinGram(1)
					.MaxGram(9)
				)
			)
		)
	)
);

Copy ExternalCode, Owner.FirstName and Owner,LastName to the "another_field" field. Now, if we index the following

client.IndexMany(new[] 
{
	new Project
	{
		Id = Guid.NewGuid(),
		ExternalCode = "foo",
	},
	new Project
	{
		Id = Guid.NewGuid(),
		Owner = new Owner
		{
			FirstName = "bar",
			LastName = "baz"		
		}
	}
}, "my-index");

client.Refresh("my-index");

We can search on the "another_field" field

client.Search<Project>(s => s
	.Index("my-index")
	.Query(q => q
		.Match(m => m
			.Field("another_field")
			.Query("foo bar baz")
		)
	)
);

which yields

{
  "took" : 64,
  "timed_out" : false,
  "_shards" : {
    "total" : 5,
    "successful" : 5,
    "failed" : 0
  },
  "hits" : {
    "total" : 2,
    "max_score" : 0.51623213,
    "hits" : [
      {
        "_index" : "my-index",
        "_type" : "project",
        "_id" : "26b9cbf6-24b8-45d1-ae63-4b3061c2ecc3",
        "_score" : 0.51623213,
        "_source" : {
          "id" : "26b9cbf6-24b8-45d1-ae63-4b3061c2ecc3",
          "isOpen" : false,
          "isDeployed" : false,
          "owner" : {
            "firstName" : "bar",
            "lastName" : "baz"
          }
        }
      },
      {
        "_index" : "my-index",
        "_type" : "project",
        "_id" : "44aae698-10bf-4771-afc4-ac822c630e0d",
        "_score" : 0.2876821,
        "_source" : {
          "id" : "44aae698-10bf-4771-afc4-ac822c630e0d",
          "isOpen" : false,
          "isDeployed" : false,
          "externalCode" : "foo"
        }
      }
    ]
  }
}