The update API allows to update a document based on a script provided. The operation gets the document (collocated with the shard) from the index, runs the script (with optional script language and parameters), and index back the result (also allows to delete, or ignore the operation). It uses versioning to make sure no updates have happened during the "get" and "reindex".

By Scriptedit

client.Update<ElasticsearchProject>(u => u
    .Id(1)
    .Script("ctx._source.country = country")
    .Params(p => p
        .Add("country", "United States")
    )
    .RetryOnConflict(3)
    .Refresh()
);

By Partial Documentedit

The update API also has a .Update<T, K> variant, where T is the document type to update, and K is the partial document to merge.

public class PartialElasticsearchProject
{
    public string Country { get; set }
}

client.Update<ElasticsearchProject, PartialElasticsearchProject>(u => u
    .Id(1)
    .Doc(new PartialElasticsearchProject { Country = "United States"})
    .RetryOnConflict(3)
    .Refresh()
);

Anonymous objects as partial documentsedit

Notice in the example above we created a custom partial object PartialElasticsearchProject, which only contains a Country property, to apply the partial update. The reason for this is that if we used the same types for both our document T) and partial document K) (i.e., typeof(T) == typeof(K)) then K would have to be fully populated with all of its values, otherwise the existing document in the index will get overriden by C# defaults for each property that wasn’t populated.

Due to this, a common use case is to just use an anonymous object as your partial document:

client.Update<ElasticsearchProject, object>(u => u
    .Id(1)
    .Doc(new { Country = "United States"})
    .RetryOnConflict(3)
    .Refresh()
);

Upsertingedit

You can insert the partial object passed to Doc into your index if it doesn’t already exist by using the DocAsUpsert method:

client.Update<ElasticsearchProject, object>(u => u
    .Id(1)
    .Doc(new { Country = "United States"})
    .DocAsUpsert()
);

Or you can pass an entirely new document to be upserted by using Upsert:

client.Update<ElasticsearchProject, object>(u => u
    .Id(1)
    .Doc(new { Country = "United States"})
    .Upsert(new ElasticsearchProject { Id = 1, Country = "United States" })
);

Id inferenceedit

In all of the above examples, we explicitly specified the id of the document in which we wanted to update. Alternatively, you can specify IdFrom, which will allow NEST to infer the id from an object instance:

client.Update<ElasticsearchProject, object>(u => u
    .IdFrom(elasticsearchProject)
    .Doc(new { Country = "United States"})
    .DocAsUpsert()
);