Language Integrated Query ( LINQ ) simplifies application development by providing a consistent query experience for objects. The C# DataStax Driver brings this convenience to Apache Cassandra™ through its LINQ component and this example shows how you can use it in C# Cassandra applications.
Contributor(s): Dave Bechberger - derived from here
Objectives
- To demonstrate how to use LINQ to insert data
- To demonstrate how to use LINQ to retrieve data
- To demonstrate how to use LINQ to update data
- To demonstrate how to use LINQ to delete data
Project Layout
- Program.cs - The main application file
- User.cs - The POCO object that maps to the Cassandra table
How this Works
This sample works by first making a connection to a Cassandra instance, this is defaulted to localhost. Once the Cluster object has been built the mapping between the User object and the users table is created using this code:
MappingConfiguration.Global.Define(
new Map<User>()
.TableName("users")
.PartitionKey(u => u.UserId)
.Column(u => u.UserId, cm => cm.WithName("id")));
One thing to notice with this code is that we are mapping the UserId property in the object to the id column in the table.
Once we have made this can connected our session this sample contains four functions:
- InsertOperations - This contains the insert operations you can perform in LINQ
- QueryOperations - This contains the query operations you can perform in LINQ
- UpdateOperations - This contains the update operations you can perform in LINQ
- DeleteOperations - This contains the delete operations you can perform in LINQ
This sample shows the most common patterns used with the LINQ Method syntax. The same functions are also available using the Query syntax. This is not an exhaustive example of the features and configuration options available within the driver. For a complete listing of the features and configuration options please check the documentation here.
Setup and Running
Prerequisites
- .NET Core 2.1 ( download )
- A Cassandra cluster is running and accessible through the contacts points
Note This application defaults to connecting to a cluster on localhost. This can be changed in Program.cs by modifying the following to your settings.
Cassandra.Cluster.Builder().AddContactPoint("127.0.0.1").Build();
Running
To run this application use the following command:
dotnet run
This will produce output similar to the following:
Retrieved 5 users Retrieved 1 users Retrieved UserId: 32e40afe-27e2-4509-9df9-a89468993d68, Name: User 0, Age: 0 Retrieved UserId: 32e40afe-27e2-4509-9df9-a89468993d68, Name: User 0, Age: 0
