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Show / Hide Table of Contents
  • Programmer's Guide
  • Client Side API Programming
    • Setting Up Development Environment
    • Basic Cache Operations
      • Initialize Cache
      • Add Data to Cache
      • Update Data in Cache
      • Fetch Data From Cache
      • Remove Data From Cache
      • Dispose Cache
    • Bulk Operations
      • Adding Collection to Cache
      • Updating Collection in Cache
      • Retrieving Collection from Cache
      • Removing Collection from Cache
      • Deleting Collection from Cache
    • Asynchronous Operations
      • Using Asynchronous Operations
      • Using Asynchronous Operations with Callback Methods
    • Groups and Subgroups
      • Adding/Updating Data Group in Cache
      • Retrieving Data Group from Cache
      • Removing Data Group from Cache
    • Tagging Data in NCache
      • Creating Tags
      • Adding Items with Tags
      • Retrieving Previously Tagged Data
      • Removing Tagged Items from Cache
    • Named Tags
    • Data Expiration Strategies
      • Using Absolute Expiration
      • Using Sliding Expiration
    • Cache Dependencies
      • Key Dependency
      • File Dependency
      • Notification based Dependencies
        • Database Dependency using SQL Server
        • Database Dependency using Oracle
      • Polling Based Dependency
      • Custom Data Source Dependency
      • Multiple Cache Sync Dependency
      • Aggregate Dependency
      • Add Dependency to Existing Item
      • Using CLR Procedures to Call NCache
    • Locking Data in NCache
      • Locking Items in Cache (Pessimistic Locking)
      • Locking Items with Cache Item Versioning (Optimistic Locking)
    • SQL Reference for NCache
      • SQL Syntax
      • Querying Samples for Operators
      • Querying Data in NCache
      • NCache Language Integrated Query (LINQ)
        • Using LINQ in NCache
        • Configuring LINQPad for NCache
        • Querying NCache Data in LINQPad
    • Event Notifications
      • Cache Level Event Notifications
      • Item Level Event Notifications
      • Custom Event Notifications
    • Publish/Subscribe (Pub/Sub) in NCache
      • Pub/Sub Topics
      • Managing Topics
      • Pub/Sub Messages
        • Message Behavior and Properties
        • Creating a Message
      • Publish Messages to Topic
      • Subscribe for Topic Messages
      • Monitoring Pub/Sub Topics
    • Continuous Query
    • Using Streams in NCache
      • Opening with Stream Modes
      • Adding and Updating Data with Streams
      • Retrieving Data from Streams
      • Closing a Stream
    • Security and Encryption
      • NCache Security
      • NCache Data Encryption
    • Data Compression
    • NCache Management API
  • Server Side API Programming
    • Cache Startup Loader
      • Components of Cache Startup Loader
      • Sample Implementation of ICacheLoader on Single Node
      • Sample Implementation of ICacheLoader with Distribution Hints
    • Data Source Providers (Backing Source)
      • Read-Through Caching
        • Configure Read-Through Provider
        • Using Read-Through with Cache Operations
      • Write-Through Caching
        • Configuring Write-Through Provider
        • Using Write-Through with Basic Operations
        • Using Write-Behind with Basic Operations
        • Using Write-Behind with Bulk Operations
        • Using Write-Behind with Async Operations
        • Monitor Write-Through Counters
    • Custom Dependency
      • Sample Implementation of Custom Dependency
      • Sample Usage of Custom Dependency
    • WAN Replication through Bridge
      • Bridge Configurations
      • Implementing Bridge Conflict Resolver
    • Entry Processor
      • Sample Implementation of IEntryProcessor Interface
      • Sample Usage of EntryProcessor
    • MapReduce
      • Sample Implementation of MapReduce Interfaces
      • Sample Usage of MapReduce
    • Aggregator
      • Sample Implementation of IValueExtractor Interface
      • Sample Implementation of IAggregator Interface
      • Sample Usage of Aggregator
    • Dynamic Compact Serialization
  • Client Side ASP.NET Features
    • ASP.NET
      • ASP.NET Session State Provider for NCache
      • Multi-Region ASP.NET Session State Provider for NCache
    • ASP.NET Core
      • Session Storage in ASP.NET Core
        • Configure NCache ASP.NET Core Session Provider
        • Configure ASP.NET Core Sessions with NCache IDistributedCache Provider
      • Multi-Region ASP.NET Core Session Provider for NCache
      • Object Caching in ASP.NET Core
    • ASP.NET SignalR
      • Using NCache Extension for SignalR
    • View State Caching
      • Configuring and Using Content Optimization
      • Group View State with Sessions
      • Limit View State Caching
      • Perform Page Level Grouping for View State
    • ASP.NET Output Cache
      • Configure ASP.NET Output Caching
      • Using ASP.NET Output Cache with Custom Hooks
  • Client Side Third Party Integrations
    • Migrating AppFabric to NCache
      • AppFabric API vs. NCache API
    • NHibernate
      • NCache as NHibernate Second Level Cache
      • Using NHibernate Query Caching
      • Configuring Database Synchronization with NHibernate
    • Entity Framework Caching Integration
      • NCache as Entity Framework Second Level Cache
      • Entity Framework Caching Config File
    • Entity Framework Core Caching
      • Installing NCache Entity Framework Core Provider
      • Configuring NCache Entity Framework Core Provider
      • Using NCache Entity Framework Core Provider
        • Caching Options for EF Core Provider
        • LINQ APIs for EF Core Provider
        • Cache Only APIs for EF Core Provider
        • Query Deferred APIs for EF Core Provider
      • Logging in NCache Entity Framework Core Provider
    • Memcached
      • NCache Memcached Gateway Approach
      • Memcached Client Plugin for .NET
    • Debug NCache Providers in Visual Studio
    • NCache for Visual Studio Extension

Key Dependency

There are situations when you want to keep a relationship among related cache data e.g. item B depends on item A. In such a situation, you would like to remove item B if item A no longer exists in cache. Here you can use key dependency to maintain this relationship.

Key dependency creates a dependency relationship between cached items. For example, you can specify a key dependency on customer's data while putting their order's data. In this way, if a customer is removed by the application or expiration then NCache will remove the order data too.

In NCache, dependent cache items and the ones on which others depend are aware of this relationship. So when an item on which other items depend is removed, all dependent items will be removed. However vice versa is not possible, i.e. on removal of an item, say Y, which has dependency on any other item, say item X, X will not be removed.

A cache item can have a dependency on any number of other items in the cache. For example, item A may depend on item X, Y and Z. Similarly, an item on which others depend can also depend on another cache item i.e. item X may depend on Y while items A and B depend on X. In short, cascaded dependencies are allowed to the nth level e.g. an item A depends on item B and B depends on item C then removal of C will result in removal of B and then A.

Note

Cyclic key dependency is not supported, i.e., Item A depends on Item B and B depends on A. Or A depends on B and B depends on C and in turn C depends on A.

An object can be specified as being dependent on another key at the time of addition. Note that the only keys present in cache can be specified as key dependency. Nonexistent key specified as key dependency will result OperationFailedException.

To utilize the API, include the following namespace in your application: Alachisoft.NCache.Runtime.Dependencies.

try
{
  cache.Add(key1, "Product:1001");
  //add key2 with dependency on key1

 cache.Add(key2, "Product:1002", new KeyDependency(key1), Cache.NoAbsoluteExpiration, Cache.NoSlidingExpiration, CacheItemPriority.Normal);

  //removing/inserting/deleting key1 will remove key2 because of its dependency
  cache.Insert(key1, "Product:1001_updated");

  object value = cache.Get(key2);
  if (value == null){
        //dependent item successfully removed
  }
  else{
        //dependent item not removed
  }
}
catch (Exception ex){
    // handle exception
}
Warning

In KeyDependency, an item can only depend on an existing item, thus all dependency keys must exist in cache before an item can depend on them.

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