EntityFramework Hooks

EntityHooks provides an extension points for EF Code First DbContext in order to hook database operations. It is designed to be easy-to-use, unit-testable and IoC compatible.

How to use

Installation

Install NuGet package from Package Manager Console:

PM> Install-Package EntityHooks

Fluent interface

Reference System.Data.Entity.Hooks.Fluent.dll assembly and include namespace in order to use fluent hooking interface.

using System.Data.Entity.Hooks.Fluent;

Logging of loading Order entities from datatbase:

dbContext.CreateHook()
        .OnLoad<Order>()
        .When(order => order.Status != 0)
        .Do(order => _logger.Write("Loaded entity " + order.Id));

Setting date when Order entity has been modified:

dbContext.CreateHook()
         .OnSave<Order>()
         .When(EntityState.Added | EntityState.Modified)
         .And(order => order.Status == 1)
         .Do(order => order.ModifiedDate = DateTime.UtcNow);

Delete Order entity if either CustomerId or CategoryId is NULL:

dbContext.CreateHook()
         .OnSave<Order>()
         .When(order => order.CustomerId == null || order.CategoryId == null)
         .Do(order => dbContext.Set<Order>().Remove(order));

However, it is still possible to attach any IDbHook implementation through fluent interface:

dbContext.OnLoad()
         .Attach(new MyFancyHook())
         .Attach(new CustomHook());
dbContext.OnSave()
         .Attach(new MyFancyHook());

How hooks are called

• Load hooks are called in the order they were registered when ObjectContext.ObjectMaterialized event occur.
• Save hooks are called in the order they were registered for each entry in DbChangeTracker before actual saving.

Hook is any class, that implements IDbHook interface.

public interface IDbHook
{
        void HookEntry(IDbEntityEntry entry);
}

IDbEntityEntry contains information about entity and it's state (EntityState enumeration). As you may have noticed, IDbHook interface don't have neither information about type of entity, which hook should be applied to, nor predicate when to invoke hook. That means, that implementors of IDbHook interface should implement their own logic, if needed.

NOTE: Instead of implementing IDbHook you may use in-build generic DbHook<TEntity> class, which calls user-specified action for entities of TEntity type and specific state.

Entity state mutability

Entity state, provided by IDbEntityEntry argument passed to IDbHook.HookEntry method, reflects current state for Load or Pre-save hooks. If hook modifies state of entity, all further invoked hooks for that entity called with new state. However, for Post-save hooks it reflects the state of entity right before saving changes, despite the fact that actual state in that case might be Unchanged.