Elasticsearch.Net is a low level Elasticsearch .NET client that has no dependencies on other libraries and is unopinionated about how you build your requests and responses.

Connectingedit

To connect to Elasticsearch running locally at http://localhost:9200 is as simple as instantiating a new instance of the client

var lowlevelClient = new ElasticLowLevelClient();

Often you may need to pass additional configuration options to the client such as the address of Elasticsearch if it’s running on a remote machine. This is where ConnectionConfiguration comes in; an instance can be instantiated to provide the client with different configuration values.

var settings = new ConnectionConfiguration(new Uri("http://example.com:9200"))
    .RequestTimeout(TimeSpan.FromMinutes(2));

var lowlevelClient = new ElasticLowLevelClient(settings);

In this example, a default request timeout was also specified that will be applied to all requests, to determine after how long the client should cancel a request. There are many other configuration options on ConnectionConfiguration to control things such as

Connecton poolsedit

ConnectionConfiguration is not restricted to being passed a single address for Elasticsearch. There are several different types of Connection pool available, each with different characteristics that can be used to configure the client. The following example uses a SniffingConnectionPool seeded with the addresses of three Elasticsearch nodes in the cluster, and the client will use this type of pool to maintain a list of available nodes within the cluster to which it can send requests in a round-robin fashion.

var uris = new[]
{
    new Uri("http://localhost:9200"),
    new Uri("http://localhost:9201"),
    new Uri("http://localhost:9202"),
};

var connectionPool = new SniffingConnectionPool(uris);
var settings = new ConnectionConfiguration(connectionPool);

var lowlevelClient = new ElasticLowLevelClient(settings);

Indexingedit

Once a client had been configured to connect to Elasticsearch, we need to get some data into the cluster to work with. Imagine we have the following Plain Old CLR Object (POCO)

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

Indexing a single instance of this POCO, either synchronously or asynchronously, is as simple as

var person = new Person
{
    FirstName = "Martijn",
    LastName = "Laarman"
};

var indexResponse = lowlevelClient.Index<byte[]>("people", "person", "1", person); 
byte[] responseBytes = indexResponse.Body;

var asyncIndexResponse = await lowlevelClient.IndexAsync<string>("people", "person", "1", person); 
string responseString = asyncIndexResponse.Body;

Both index requests will index the document to the endpoint /people/person/1.

An anonymous type can also be used to represent the document to index

var person = new
{
    FirstName = "Martijn",
    LastName = "Laarman"
};

var indexResponse = await lowlevelClient.IndexAsync<Stream>("people", "person", "1", person);
Stream responseStream = indexResponse.Body; 

Whether you use an instance of a class, anonymous type, string, etc. they all are implicitly converted to an instance of PostData<T> that the method accepts. Check out the documentation on Post Data to see the other types that are supported.

The generic type parameter on the method specifies the type of the response body. In the last example, we return the response stream from Elasticsearch, forgoing any deserialization.

Bulk indexingedit

If you need to index many documents, Elasticsearch has a Bulk API that can be used to perform many operations in one request

var people = new object[]
{
    new { index = new { _index = "people", _type = "person", _id = "1"  }},
    new { FirstName = "Martijn", LastName = "Laarman" },
    new { index = new { _index = "people", _type = "person", _id = "2"  }},
    new { FirstName = "Greg", LastName = "Marzouka" },
    new { index = new { _index = "people", _type = "person", _id = "3"  }},
    new { FirstName = "Russ", LastName = "Cam" },
};

var indexResponse = lowlevelClient.Bulk<Stream>(people);
Stream responseStream = indexResponse.Body;

The client will serialize each item seperately and join items up using the \n character as required by the Bulk API. Refer to the Elasticsearch Bulk API documentation for further details and supported operations.

Searchingedit

Now that we have indexed some documents we can begin to search for them.

The Elasticsearch Query DSL can be expressed using an anonymous type within the request

var searchResponse = lowlevelClient.Search<string>("people", "person", new
{
    from = 0,
    size = 10,
    query = new
    {
        match = new
        {
            field = "firstName",
            query = "Martijn"
        }
    }
});

var successful = searchResponse.Success;
var responseJson = searchResponse.Body;

responseJson now holds a JSON string for the response. The search endpoint for this query is /people/person/_search and it’s possible to search over multiple indices and types by changing the arguments supplied in the request for index and type, respectively.

Strings can also be used to express the request

var searchResponse = lowlevelClient.Search<byte[]>("people", "person", @"
{
    ""from"": 0,
    ""size"": 10,
    ""query"": {
        ""match"": {
            ""field"": ""firstName"",
            ""query"": ""Martijn""
        }
    }
}");

var responseBytes = searchResponse.Body;

As you can see, using strings is a little more cumbersome than using anonymous types because of the need to escape double quotes, but it can be useful at times nonetheless. responseBytes will contain the bytes of the response from Elasticsearch.

Handling Errorsedit

By default, Elasticsearch.Net is configured not to throw exceptions if a HTTP response status code is returned that is not in the 200-300 range, nor an expected response status code allowed for a given request e.g. checking if an index exists can return a 404.

The response from low level client calls provides a number of properties that can be used to determine if a call is successful

var searchResponse = lowlevelClient.Search<byte[]>("people", "person", new { match_all = new {} });

var success = searchResponse.Success; 
var successOrKnownError = searchResponse.SuccessOrKnownError; 
var serverError = searchResponse.ServerError; 
var exception = searchResponse.OriginalException; 

Using these details, it is possible to make decisions around what should be done in your application.

The default behaviour of not throwing exceptions can be changed by setting .ThrowExceptions() on ConnectionConfiguration

var settings = new ConnectionConfiguration(new Uri("http://example.com:9200"))
    .ThrowExceptions();

var lowlevelClient = new ElasticLowLevelClient(settings);

And if more fine grained control is required, custom exceptions can be thrown using .OnRequestCompleted() on ConnectionConfiguration

var settings = new ConnectionConfiguration(new Uri("http://example.com:9200"))
    .OnRequestCompleted(apiCallDetails =>
    {
        if (apiCallDetails.HttpStatusCode == 418)
        {
            throw new TimeForACoffeeException();
        }
    });

var lowlevelClient = new ElasticLowLevelClient(settings);