DataStax C# Driver for Apache Cassandra

A modern, feature-rich and highly tunable C# client library for Apache Cassandra (2.0+) using Cassandra’s binary protocol and Cassandra Query Language v3.

It also provides additional features for DataStax Enterprise:

• IAuthenticator implementations that use the authentication scheme negotiation in the server-side DseAuthenticator.
• DSE graph integration.
• Serializers for geospatial types which integrate seamlessly with the driver.

The driver supports .NET Framework 4.5.2+ and .NET Core 2.1+ (LTS).

Installation

Get it on Nuget

PM> Install-Package CassandraCSharpDriver

Features

• Sync and Async API
• Simple, Prepared, and Batch statements
• Asynchronous IO, parallel execution, request pipelining
• Connection pooling
• Auto node discovery
• Automatic reconnection
• Configurable load balancing and retry policies
• Works with any cluster size
• Linq2Cql and Ado.Net support

Documentation

• Documentation index
• API docs
• FAQ
• Version compatibility matrix
• Developing applications with DataStax drivers

Getting Help

You can use the project Mailing list or create a ticket on the Jira issue tracker. Additionally, you can ask questions on DataStax Community.

Upgrading from previous versions or from the DSE C# driver

If you are upgrading from previous versions of the driver, visit the Upgrade Guide.

If you are upgrading from the DSE C# driver (which has been unified with this driver), there’s also a section related to this on the Upgrade Guide.

Basic Usage

var cluster = Cluster.Builder()
                     .AddContactPoints("host1")
                     .Build();
// Connect 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);

Authentication

If you are using the PasswordAuthenticator which is included in the default distribution of Apache Cassandra, you can use the Builder.WithCredentials method or you can explicitly create a PlainTextAuthProvider instance.

For clients connecting to a DSE cluster secured with DseAuthenticator, two authentication providers are included (on the Cassandra.DataStax.Auth namespace):

• DsePlainTextAuthProvider: plain-text authentication;
• DseGssapiAuthProvider: GSSAPI authentication.

To configure a provider, pass it when initializing the cluster:

using Cassandra;
using Cassandra.DataStax.Auth;

ICluster cluster = Cluster.Builder()
    .AddContactPoint("127.0.0.1")
    .WithAuthProvider(new DseGssapiAuthProvider())
    .Build();

DataStax Graph

ISession has dedicated methods to execute graph queries:

using Cassandra.DataStax.Graph;

session.ExecuteGraph("system.createGraph('demo').ifNotExist().build()");

GraphStatement s1 = new SimpleGraphStatement("g.addV(label, 'test_vertex')").SetGraphName("demo");
session.ExecuteGraph(s1);

GraphStatement s2 = new SimpleGraphStatement("g.V()").SetGraphName("demo");
GraphResultSet rs = session.ExecuteGraph(s2);

IVertex vertex = rs.First().To<IVertex>();
Console.WriteLine(vertex.Label);

Graph options

You can set default graph options when initializing the cluster. They will be used for all graph statements. For example, to avoid repeating SetGraphName("demo") on each statement:

ICluster cluster = Cluster.Builder()
    .AddContactPoint("127.0.0.1")
    .WithGraphOptions(new GraphOptions().SetName("demo"))
    .Build();

If an option is set manually on a GraphStatement, it always takes precedence; otherwise the default option is used. This might be a problem if a default graph name is set, but you explicitly want to execute a statement targeting system, for which no graph name must be set. In that situation, use GraphStatement.SetSystemQuery():

GraphStatement s = new SimpleGraphStatement("system.createGraph('demo').ifNotExist().build()")
    .SetSystemQuery();
session.ExecuteGraph(s);

Query execution

As explained, graph statements can be executed with the session’s ExecuteGraph method. There is also an asynchronous equivalent called ExecuteGraphAsync that returns a Task that can be awaited upon.

Handling results

Graph queries return a GraphResultSet, which is a sequence of GraphNode elements:

GraphResultSet rs = session.ExecuteGraph(new SimpleGraphStatement("g.V()"));

// Iterating as IGraphNode
foreach (IGraphNode r in rs)
{
    Console.WriteLine(r);
}

IGraphNode represents a response item returned by the server. Each item can be converted to the expected type:

GraphResultSet rs = session.ExecuteGraph(new SimpleGraphStatement("g.V()"));
IVertex vertex = rs.First().To<IVertex>();
Console.WriteLine(vertex.Label);

Additionally, you can apply the conversion to all the sequence by using GraphResultSet.To<T>() method:

foreach (IVertex vertex in rs.To<IVertex>())
{
    Console.WriteLine(vertex.Label);
}

GraphNode provides implicit conversion operators to string, int, long and others in order to improve code readability, allowing the following C# syntax:

var rs = session.ExecuteGraph(new SimpleGraphStatement("g.V().has('name', 'marko').values('location')"));
foreach (string location in rs)
{
    Console.WriteLine(location);
}

GraphNode inherits from DynamicObject, allowing you to consume it using the dynamic keyword and/or as a dictionary.

dynamic r = session.ExecuteGraph(new SimpleGraphStatement("g.V()")).First();

Parameters

Graph query parameters are always named. Parameter bindings are passed as an anonymous type or as a IDictionary<string, object> alongside the query:

session.ExecuteGraph("g.addV(label, vertexLabel)", new { vertexLabel = "test_vertex_2" });

Note that, unlike in CQL, Gremlin placeholders are not prefixed with “:”.

Prepared statements with DSE Graph

Prepared graph statements are not supported by DSE Graph.

Geospatial types

DSE 5 comes with a set of additional types to represent geospatial data: PointType, LineStringType and PolygonType:

cqlsh> CREATE TABLE points_of_interest(name text PRIMARY KEY, coords 'PointType');
cqlsh> INSERT INTO points_of_interest (name, coords) VALUES ('Eiffel Tower', 'POINT(48.8582 2.2945)');

The DSE driver includes C# representations of these types, that can be used directly in queries:

using Cassandra.Geometry;

Row row = session.Execute("SELECT coords FROM points_of_interest WHERE name = 'Eiffel Tower'").First();
Point coords = row.GetValue<Point>("coords");

var statement = new SimpleStatement("INSERT INTO points_of_interest (name, coords) VALUES (?, ?)",
    "Washington Monument",
    new Point(38.8895, 77.0352));
session.Execute(statement);

Compatibility

• Apache Cassandra versions 2.0 and above.
• DataStax Enterprise versions 4.8 and above.
• .NET Framework versions 4.5.2 and above and .NET Core versions 2.1 and above.

Note: DataStax products do not support big-endian systems.

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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

© DataStax, Inc.

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.