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Changing serializers

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Changing serializers

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NEST uses JSON.Net to serialize requests to and deserialize responses from JSON.

Whilst JSON.Net does a good job of serialization, you may wish to use your own JSON serializer for a particular reason. Elasticsearch.Net and NEST make it easy to replace the default serializer with your own.

If you are looking to change how the default serializer works, check out Modifying the default serializer.

The main component needed is to provide an implementation of IElasticsearchSerializer

public class CustomSerializer : IElasticsearchSerializer
{
    public T Deserialize<T>(Stream stream)
    {
        // provide deserialization implementation
        throw new NotImplementedException();
    }

    public Task<T> DeserializeAsync<T>(Stream responseStream, CancellationToken cancellationToken = default(CancellationToken))
    {
        // provide an asynchronous deserialization implementation
        throw new NotImplementedException();
    }

    public void Serialize(object data, Stream writableStream, SerializationFormatting formatting = SerializationFormatting.Indented)
    {
        // provide a serialization implementation
        throw new NotImplementedException();
    }

    public IPropertyMapping CreatePropertyMapping(MemberInfo memberInfo)
    {
        // provide an implementation, if the serializer can decide how properties should be mapped.
        // Otherwise return null.
        return null;
    }
}

Changing serializers in Elasticsearch.Net

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For Elasticsearch.Net, an implementation of IElasticsearchSerializer is all that is needed and a delegate can be passed to ConnectionConfiguration that will be called to construct an instance of the serializer

var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var connection = new HttpConnection();
var connectionConfiguration =
    new ConnectionConfiguration(pool, connection, configuration => new CustomSerializer()); 

var lowlevelClient = new ElasticLowLevelClient(connectionConfiguration);

delegate gets passed ConnectionConfiguration and creates a serializer.

Changing serializers in NEST

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With NEST however, an implementation of ISerializerFactory in addition to an implementation of IElasticsearchSerializer is required.

public class CustomSerializerFactory : ISerializerFactory
{
    public IElasticsearchSerializer Create(IConnectionSettingsValues settings) => new CustomSerializer();

    public IElasticsearchSerializer CreateStateful(IConnectionSettingsValues settings, JsonConverter converter) =>
        new CustomSerializer();
}

With an implementation of ISerializerFactory that can create instances of our custom serializer, hooking this into ConnectionSettings is straightfoward

var pool = new SingleNodeConnectionPool(new Uri("http://localhost:9200"));
var connection = new HttpConnection();
var connectionSettings =
    new ConnectionSettings(pool, connection, new CustomSerializerFactory());

var client = new ElasticClient(connectionSettings);

The implementation for how custom serialization is configured within the client is subject to change in the next major release. NEST relies heavily on stateful deserializers that have access to details from the original request for specialized features such a covariant search results.

You may have noticed that this requirement leaks into the ISerializerFactory abstraction in the form of the CreateStateful method signature. There are intentions to replace or at least internalize the usage of JSON.Net within NEST in the future and in the process, simplifying how custom serialization can be integrated.

This has provided you details on how to implement your own custom serialization, but a much more common scenario amongst NEST client users is the desire to change the serialization settings of the default JSON.Net serializer. Take a look at modifying the default serializer to see how this can be done.

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