WCF service using Cassandra

Explore WCF service using Cassandra

This is a brief tutorial on how to use Apache Cassandra’s user-defined types (UDT) with C# Windows Communication Foundation (WCF) rest service.

Summary of the Steps

1. Create user-defined type(Udt)
2. Create a mapper object for Udt in C#
3. Register C# Udt object
4. Connect to Cassandra cluster and create session
5. Define WCF DataContract and OperationContract
6. Host in IIS

1. Create User Defined Type

Create a user-defined type for address, fullname and users. There is more info in this datastax tutorial for UDT.

2. Create a mapper object for UDT in ‘C#’

Create a mapper object(CqlPoco). In our case that will also be a data contract. For more data types mapping, refer to CQL data types to C# types.
Class for address:
  public class Address
   {
       public string Street { get; set; }
       public string City { get; set; }
       public int ZipCode { get; set; }
       public IEnumerable<string> Phones { get; set; }
   }
 
Class for fullname:
public class FullName
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
}
 
Finally, a class which represent a row in cassandra users table:
  public class User
   {
       public Guid Id { get; set; }
       public IDictionary<string, Address> Addresses { get; set; }
       public IEnumerable<FullName> DirectReport { get; set; }
       public FullName Name { get; set; }
   }
 

3. Register C# UDT object

Configure the POCO object to the Apache Cassandra driver using mapper component.
Map user-defined type (FullName and Address):
session.UserDefinedTypes.Define(
         UdtMap.For<FullName>(),
         UdtMap.For<Address>()
            .Map(a => a.Street, “street”)
            .Map(a => a.City, “city”)
            .Map(a => a.ZipCode, “zip_code”)
            .Map(a => a.Phones, “phones”)
     );
 
In most of the cases, mapper will do the mapping for simple type like Fullname but a better controlled mapping is also possible, like Address, where it is mapped field by field.
Map User class representing a row in a table:
 Cassandra.Mapping.MappingConfiguration.Global.Define(new Map<User>().TableName(“users”)
               .Column(c => c.Id, cm => cm.WithName(“id”))
               .Column(c => c.Addresses, cm => cm.WithName(“addresses”).WithFrozenKey())
               .Column(c => c.DirectReport, cm => cm.WithName(“direct_reports”).WithFrozenValue()));
 

4. Connect to Cassandra cluster and create session

Cassandra and C# setup is complete, so now connect to cluster and use it.
        cluster = Cluster.Builder().AddContactPoint(“127.0.0.1”).Build();
         session = cluster.Connect(“mykeyspace”);

         var users = new Table<User>(session);
         var user = users.
             Where(u => u.Id == Guid.Parse(guid))
             .FirstOrDefault()
             .Execute();

 

5. Setting up a WCF

Decorate the POCO we just created with the DataMember attribute, declare OperationContract and provide a definition. Register mapping (see step 3) with a memoization library. In this case, service constructor was leveraged to initialise the mapping.
  public class UserService : IUserService
   {
       static UserServiceLibrary.Data.DataService dataService;
       static UserService()
       {
           dataService = new UserServiceLibrary.Data.DataService();
       }
   }    
 

6. Hosting WCF service

WCF rest service can be self-hosted using WebServiceHost:
WebServiceHost webhost =  new WebServiceHost(typeof(UserService));
           try
           {
               webhost.Open();
               Console.ReadLine();
               webhost.Close();

           }
           catch (Exception e)
           {
               Console.WriteLine(e);
               webhost.Abort();
           }
       }
 
WCF can also be  hosted in IIS to take the advantage of on-demand loading and application pool using:
<%@ ServiceHost Service=”WcfWebService.UserService”
Factory=”System.ServiceModel.Activation.WebServiceHostFactory”%>
 
The complete source code for this tutorial can be found at Github.