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Cassandra Day NY 2014: Getting Started with the DataStax C# Driver


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So you’ve grabbed the latest 2.0 beta of DataStax C# driver from NuGet. Now what? In this talk, Luke will walk you through some of the basics of the C# driver--how to bootstrap the driver and connect to a cluster, execute statements, and retrieve result sets. Wondering what the difference between a PreparedStatement and a SimpleStatement is? Not sure what the appropriate lifetime for a Cluster or a Session object is and whether you should reuse one (from multiple threads)? What about ADO.NET and LINQ support? We’ll cover this and more, so that you can get on with building applications on top of Cassandra and .NET.

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Cassandra Day NY 2014: Getting Started with the DataStax C# Driver

  1. 1. Getting Started with DataStax C# Driver Luke Tillman Language Evangelist @LukeTillman
  2. 2. Life as the .NET Language Evangelist
  3. 3. Where do I get the driver? • NuGet • GitHub •
  4. 4. Bootstrapping the Driver
  5. 5. Cluster • Singleton - one per application • Use the Builder Cluster cluster = Cluster.Builder() .AddContactPoint("") .Build();
  6. 6. Cluster • Fluent Interface with Lots of Options var authProvider = new PlainTextAuthProvider("username", "password"); var queryOptions = new QueryOptions() .SetConsistencyLevel(ConsistencyLevel.LocalQuorum) .SetPageSize(1000); Cluster cluster = Cluster.Builder().AddContactPoint("") .WithSSL() .WithQueryOptions(queryOptions) .WithAuthProvider(authProvider) .Build();
  7. 7. Session • Singleton per keyspace • Inspired by the (N)Hibernate session object • Get it from your Cluster object ISession session = cluster.Connect("killrvideo");
  8. 8. Sample IoC Container Registration // Use the Cluster builder to create a cluster Cluster cluster = Cluster.Builder().AddContactPoint("").Build(); // Use the cluster to connect a session to the appropriate keyspace ISession session = cluster.Connect("killrvideo"); // Register both Cluster and ISession instances with Windsor (as // Singletons since it will reuse the instance) container.Register( Component.For<Cluster>().Instance(cluster), Component.For<ISession>().Instance(session) );
  9. 9. Creating Statements
  10. 10. Types of Statements • SimpleStatement • PreparedStatement / BoundStatement • BatchStatement
  11. 11. SimpleStatement • It’s… simple? • Can use bind parameters • Useful for one-off statements or dynamic CQL where you can’t prepare it var statement = new SimpleStatement("SELECT * FROM users WHERE userid = ?"); statement = statement.Bind(145);
  12. 12. PreparedStatement / BoundStatement • Pay the cost of Prepare once (server roundtrip) • Save the PreparedStatement instance and reuse PreparedStatement prepared = session.Prepare( "SELECT * FROM user_credentials WHERE email = ?");
  13. 13. PreparedStatement / BoundStatement • Bind variable values to get BoundStatement for execution • Execution only has to send variable values • You will use these all the time BoundStatement bound = prepared.Bind("");
  14. 14. BatchStatement • Add Simple/Bound statements to a batch BoundStatement bound = prepared.Bind(video.VideoId, video.Name); var simple = new SimpleStatement( "UPDATE videos SET name = ? WHERE videoid = ?" ).Bind(video.Name, video.VideoId); // Use an atomic batch to send over all the mutations var batchStatement = new BatchStatement(); batchStatement.AddQuery(bound); batchStatement.AddQuery(simple);
  15. 15. BatchStatement • Batches are Logged, atomic (by default) and this is the most common use case • Set the batch type to use a different type of batch • Counters have their own batch type (can’t mix) var batch = new BatchStatement().SetBatchType(BatchType.Unlogged);
  16. 16. Statements – You’ve Got Options • Simple and Bound statements have options that can be set at the Statement level • Consistency Level • Retry Policy • Paging Size (for automatic paging, we’ll come back to this) • Tracing • If not set at the statement level, defaults set when configuring/building the Cluster are used
  17. 17. Statements – You’ve Got Options • Example of binding a PreparedStatement and setting available options: IStatement bound = prepared.Bind("") .SetPageSize(100) .SetConsistencyLevel(ConsistencyLevel.LocalOne) .SetRetryPolicy(new DefaultRetryPolicy()) .EnableTracing();
  18. 18. Executing Statements and Getting the Results
  19. 19. Executing Statements • Use your Session object to execute statements • You can execute statements synchronously or asynchronously • Synchronous • Asynchronous • Execute methods return a RowSet RowSet rows = await _session.ExecuteAsync(boundStatement); RowSet rows = _session.Execute(boundStatement);
  20. 20. RowSet • RowSet implements IEnumerable<Row> • Use GetValue<T> method on a Row to get a column’s value • By column name • By ordinal (position)
  21. 21. RowSet • Because RowSet implements IEnumerable<Row>: • Iterate with foreach RowSet rows = await _session.ExecuteAsync(boundStatement); foreach (Row row in rows) { returnList.Add(new VideoPreview { VideoId = row.GetValue<Guid>("videoid"), AddedDate = row.GetValue<DateTimeOffset>("added_date"), Name = row.GetValue<string>("name") }); }
  22. 22. RowSet • Because RowSet implements IEnumerable<Row>: • Project Rows with LINQ to Objects Select() RowSet rows = await _session.ExecuteAsync(boundStatement); var returnList = rows.Select(row => new VideoPreview { VideoId = row.GetValue<Guid>(0), AddedDate = row.GetValue<DateTimeOffset>(1), Name = row.GetValue<string>(2) }).ToList();
  23. 23. RowSet • Because RowSet implements IEnumerable<Row>: • Get a single row with LINQ to Objects Single() or SingleOrDefault() RowSet rows = await _session.ExecuteAsync(boundStatement); Row row = rows.SingleOrDefault();
  24. 24. CQL 3 Data Types to .NET Types Full listing available in driver docs CQL 3 Data Type .NET Type bigint, counter long boolean bool decimal, float float double double int int uuid, timeuuid System.Guid text, varchar string (Encoding.UTF8) timestamp System.DateTimeOffset varint System.Numerics.BigIntege r
  25. 25. Driver 2.0 Features
  26. 26. Lightweight Transactions (LWT) • Use when you don’t want writes to step on each other • AKA Linearizable Consistency • Serial Isolation Level • Be sure to read the fine print: has a latency cost associated with using it, so use only where needed • The canonical example: unique user accounts
  27. 27. Lightweight Transactions (LWT) • Returns a column called [applied] indicating success/failure • Different from the relational world where you might expect an Exception (i.e. var statement = new SimpleStatement("INSERT INTO user_credentials (email, password) VALUES (?, ?) IF NOT EXISTS"); statement = statement.Bind("", "Password1!"); RowSet rows = await _session.ExecuteAsync(statement); var userInserted = rows.Single().GetValue<bool>("[applied]");
  28. 28. Automatic Paging • The Problem: Loading big result sets into memory is a recipe for disaster (OutOfMemoryExceptions, etc.) • Better to load and process a large result set in pages (chunks) • Doing this manually with Cassandra prior to 2.0 was a pain
  29. 29. Automatic Paging • Set a page size on a statement (or will use default from Cluster) • Iterate over the resulting RowSet • As you iterate, new pages are fetched transparently when the Rows in the current page are exhausted • Will allow you to iterate until all pages are exhausted boundStatement = boundStatement.SetPageSize(100); RowSet rows = await _session.ExecuteAsync(boundStatement); foreach (Row row in rows) { }
  30. 30. Typical Paging in a Web Application • Show page of records in UI and allow user to navigate • Automatic Paging – this is not the feature you are looking for
  31. 31. Where To Go From Here
  32. 32. LINQ to CQL • Comes in the NuGet package as Cassandra.Data.Linq • Has support for all CRUD operations • Start by decorating the objects you’ll be querying with Table, Column, and PartitionKey attributes
  33. 33. LINQ to CQL [Table("user_credentials")] public class UserCredentials { [Column("email")] [PartitionKey] public string EmailAddress { get; set; } [Column("password")] public string Password { get; set; } [Column("userid")] public Guid UserId { get; set; } }
  34. 34. LINQ to CQL • Then query with LINQ using the Session’s GetTable<T> method as your starting point public UserCredentials GetCredentials(string emailAddress) { IEnumerable<UserCredentials> results = _session.GetTable<UserCredentials>() .Where(uc => uc.EmailAddress == emailAddress) .Execute(); return results.SingleOrDefault(); }
  35. 35. ADO.NET Support • Available in the NuGet package as Cassandra.Data • Allows you to use your “favorite” ADO.NET objects like DbConnection, DbCommand, etc. to query Cassandra • My recommendation? Avoid it. • Cassandra concepts don’t always map well to
  36. 36. The KillrVideo Sample Application • Many of this presentation’s samples are taken from here •
  37. 37. What Next? • Data Modeling, Data Modeling, Data Modeling • Planet Cassandra ( • Links to videos, drivers, documentation, tutorials, etc. Follow me on Twitter for updates: @LukeTillman