Configuring NCache Entity Framework Core Provider

This section focuses on configuration required to use NCache as second level cache in an Entity Framework application.

This requires serializing entities and specifying NCache specific configurations in DbContext of your EF applications.

NCache 4.9 SP1 onwards, NCache also provides the flexibility to resync cache if items are invalidated due to expiration or eviction. This keeps the data afresh in the cache, and reduces network trips to the database to fetch the expired items.

Serializing Entities

All entities of the database model need to be serialized in order to be stored in NCache, therefore they have to be marked as serializable.

[Serializable]
public partial class Customers
{
     // Getters setters
}

Specifying Cache Configurations in DbContext

To configure NCache in Entity Framework applications, NCache provides configurable cache properties which are specified in the DbContext. The NCacheConfiguration class allows specifying the properties and configuring the logger for your application:

Important

It is advised to configure NCache in either the database context or the entry point of the application, else an exception is thrown, prompting that NCache initialization configuration has not been provided.

The following code sample configures NCache for the EF application in an extended DbContext class with SqlServer DependencyType and CacheInitParams specifying Cluster Port, Retry Interval and Connection Retries for the cache. The configurations CacheId and ConnString have been specified in App.config:

public partial class NorthwindContext : DbContext
{
...
    protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
    {
        // Parameters specified in App.config
        string cacheId = ConfigurationManager.AppSettings["CacheId"];
        string connString = ConfigurationManager.AppSettings["ConnString"];

        // configure cache with SQLServer DependencyType and CacheInitParams
        CacheInitParams initParams = new CacheInitParams();
        initParams.RetryInterval = 3;
        initParams.ConnectionRetries = 2;
        initParams.Port = 7801;

        NCacheConfiguration.Configure(cacheId, DependencyType.SQLServer, initParams);

        optionsBuilder.UseSqlServer(connString);
    }
}

Create and Deploy EF Core Resync Provider

NCache provides EFDefaultResyncProvider which further implements IReadThruProvider. This requires instantiating the DbContext which has been created in the previous step. Once the provider has been created, you need to deploy it as Read-Through Provider using NCache Manager.

public class EFDefaultProvider : EFDefaultResyncProvider
{
    protected override DbContext InitializedDbContext()
    {
        return new NorthwindContext();
    }
}

Deploy the provider using the steps explained in Administrators' Guide.

Default Schema Configuration for SQL Dependency

Database dependency queries differ slightly from regular SQL queries. Hence SQL Server does not accept the query specified as valid. To avoid this issue, dbo needs to be appended before the table name where default schema is set as dbo. This can be done by adding the following line of code in the OnModelCreating method in DbContext class:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
     modelBuilder.HasDefaultSchema("dbo"); //add this line for SQL dependency

     //rest of the entity model code goes here
}

The query now generated can be used to configure database dependency.

Configuration Options

The configuration options provided by NCacheConfiguration are:

Member	Type	Description
`CacheId`	`string`	Specifies the name of the cache to be used for serving in the Entity Framework application. If no cache name is specified, a configuration exception will be thrown.
`DatabaseType`	`DependencyType`	Enum to inform the cache about the database being used by Entity Framework. The values are: `Other` = 0 `SqlServer` = 1 `Oracle` = 2 This enum deals with data invalidation. If data is updated in the database, NCache removes the cached queries based on the affected entities so that new data can be served from the data source on the next query to prevent usage of stale data. NOTE: Entity Framework Core does not yet provide support for Oracle, so it should be avoided. NOTE: In case of `DependencyType` set as `Other`, database dependency is not created. NOTE: In case of `DependencyType` set as `SqlServer`, SQL service broker must be enabled on SQL server as data invalidation requires SQL dependency. SQL dependency also requires special configuration change to `DbContext`. See below for detail.
`InitParams`	`CacheInitParams`	Class that contains customized parameters to initialize cache with user specified configurations.
`IsConfigured`	`bool`	Specifies whether `DbContext` has been configured with any overriding options or not.

Method	Description
`Configure`	Configures the cache to be used for serving in the Entity Framework application. This sets the configuration of the cache according to the user specified properties. It takes in the cache ID, database dependency type and any optional initialization parameters for the cache.
`ConfigureLogger`	Configures instance(s) of `Microsoft.Extensions.Logging.ILogger` via an `Microsoft.Extensions.Logging.ILoggerFactory` in order to log details of operations from the caching provider.
`IsLoggerEnabled`	Specifies whether the logger has been enabled at the specified log level or not.