DataStax C# Driver for Apache Cassandra

A C# client driver for Apache Cassandra. This driver works exclusively with the Cassandra Query Language version 3 (CQL3) and Cassandra's binary protocol.

Installation

Get it on Nuget

PM> Install-Package CassandraCSharpDriver

Features

Connection pooling
Node discovery
Automatic failover
Several load balancing and retry policies
Result paging
Query batching
Linq2Cql and Ado.Net support

Documentation

Getting Help

You can use the project Mailing list or create a ticket on the Jira issue tracker.

Upgrading from previous versions

If you are upgrading from the 2.1 branch of the driver, be sure to have a look at the upgrade guide.

If you are upgrading from the 1.x branch of the driver, follow the upgrade guide to 2.0, and then the above document.

Basic Usage

//Create a cluster instance using 3 cassandra nodes.
var cluster = Cluster.Builder()
  .AddContactPoints("host1", "host2", "host3")
  .Build();
//Create connections to the nodes using a keyspace
var session = cluster.Connect("sample_keyspace");
//Execute a query on a connection synchronously
var rs = session.Execute("SELECT * FROM sample_table");
//Iterate through the RowSet
foreach (var row in rs)
{
  var value = row.GetValue<int>("sample_int_column");
  //do something with the value
}

Prepared statements

Prepare your query once and bind different parameters to obtain best performance.

//Prepare a statement once
var ps = session.Prepare("UPDATE user_profiles SET birth=? WHERE key=?");

//...bind different parameters every time you need to execute
var statement = ps.Bind(new DateTime(1942, 11, 27), "hendrix");
//Execute the bound statement with the provided parameters
session.Execute(statement);

Batching statements

You can execute multiple statements (prepared or unprepared) in a batch to update/insert several rows atomically even in different column families.

//Prepare the statements involved in a profile update once
var profileStmt = session.Prepare("UPDATE user_profiles SET email=? WHERE key=?");
var userTrackStmt = session.Prepare("INSERT INTO user_track (key, text, date) VALUES (?, ?, ?)");
//...you should reuse the prepared statement
//Bind the parameters and add the statement to the batch batch
var batch = new BatchStatement()
  .Add(profileStmt.Bind(emailAddress, "hendrix"))
  .Add(userTrackStmt.Bind("hendrix", "You changed your email", DateTime.Now));
//Execute the batch
session.Execute(batch);

Asynchronous API

Session allows asynchronous execution of statements (for any type of statement: simple, bound or batch) by exposing the ExecuteAsync method.

//Execute a statement asynchronously using await
var rs = await session.ExecuteAsync(statement);

Avoid boilerplate mapping code

The driver features a built-in Mapper and Linq components that can use to avoid boilerplate mapping code between cql rows and your application entities.

User user = mapper.Single<User>("SELECT name, email FROM users WHERE id = ?", userId);

See the driver components documentation for more information.

Automatic pagination of results

You can iterate indefinitely over the RowSet, having the rows fetched block by block until the rows available on the client side are exhausted.

var statement = new SimpleStatement("SELECT * from large_table");
//Set the page size, in this case the RowSet will not contain more than 1000 at any time
statement.SetPageSize(1000);
var rs = session.Execute(statement);
foreach (var row in rs)
{
  //The enumerator will yield all the rows from Cassandra
  //Retrieving them in the back in blocks of 1000.
}

User defined types mapping

You can map your Cassandra User Defined Types to your application entities.

For a given udt

CREATE TYPE address (
  street text,
  city text,
  zip_code int,
  phones set<text>
);

For a given class

public class Address
{
  public string Street { get; set; }
  public string City { get; set; }
  public int ZipCode { get; set; }
  public IEnumerable<string> Phones { get; set;}
}

You can either map the properties by name

//Map the properties by name automatically
session.UserDefinedTypes.Define(
  UdtMap.For<Address>()
);

Or you can define the properties manually

session.UserDefinedTypes.Define(
  UdtMap.For<Address>()
    .Map(a => a.Street, "street")
    .Map(a => a.City, "city")
    .Map(a => a.ZipCode, "zip_code")
    .Map(a => a.Phones, "phones")
);

You should map your UDT to your entity once and you will be able to use that mapping during all your application lifetime.

var rs = session.Execute("SELECT id, name, address FROM users where id = x");
var row = rs.First();
//You can retrieve the field as a value of type Address
var userAddress = row.GetValue<Address>("address");
Console.WriteLine("user lives on {0} Street", userAddress.Street);

Setting cluster and statement execution options

You can set the options on how the driver connects to the nodes and the execution options.

//Example at cluster level
var cluster = Cluster
  .Builder()
  .AddContactPoints(hosts)
  .WithCompression(CompressionType.LZ4)
  .WithLoadBalancingPolicy(new DCAwareRoundRobinPolicy("west"));

//Example at statement (simple, bound, batch) level
var statement = new SimpleStatement(query)
  .SetConsistencyLevel(ConsistencyLevel.Quorum)
  .SetRetryPolicy(DowngradingConsistencyRetryPolicy.Instance)
  .SetPageSize(1000);

Building and running the tests

You can use Visual Studio or msbuild to build the solution.

Check the documentation for building the driver from source and running the tests.

License

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.

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