Signum Documentation

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Schema.EntityEvents

EntityEvents<T> is a generic class that contains the events that will when Signum.Engine interacts with your entities (i.e. Save, Retrieve, etc..).

Schema class gives you two ways of accessing EntityEvents:

public class Schema
{
   public EntityEvents<Entity> EntityEventsGlobal { get; }
   
   public EntityEvents<T> EntityEvents<T>()
       where T : Entity
}
  • EntityEventsGlobal property lets you attach/detach event for every Entity.
  • EntityEvents<T> method lets you attach/detach event for one particular entity type T.

EntityEvent<T> class defines a bunch of events:

public class EntityEvents<T> : IEntityEvents
            where T : Entity
{
    public event PreSavingEventHandler<T> PreSaving;
    public event SavingEventHandler<T> Saving;
    public event SavedEventHandler<T> Saved;

    public event RetrievedEventHandler<T> Retrieved;

    public event FilterQueryEventHandler<T> FilterQuery;

    public event PreUnsafeDeleteHandler<T> PreUnsafeDelete;
    public event PreUnsafeDeleteMlistHandler<T> PreUnsafeMListDelete;
    public event PreUnsafeUpdateHandler<T> PreUnsafeUpdate;
    public event PreUnsafeInsertHandler<T> PreUnsafeInsert;
}

PreSaving

PreSaving is executed before saving. Allows changing the object graph but, if done, graphModified must be set to true.

public delegate void PreSavingEventHandler<T>(T ident, ref bool graphModified) where T : Entity;

Consider overriding ModifiableEntity.PreSaving instead if you have control of the entity and the changes do not require interacting with the Logic assembly.

//in BugLogic.Start..

sb.Schema.EntityEvents<BugEntity>().PreSaving += Bug_PreSaving;

static void Bug_PreSaving(BugEntity bug, ref bool graphModified)
{
   if(bug.LastUser.Is(UserEntity.Current))
      return;

   bug.LastUser = UserEntity.Current;
   graphModified = true;
}

Saving

Saving is executed after PreSaving is executed for all the entities in the graph. The graph is validated, and the modifications propagated. Let you test the final entity that will be saved in the database.

public delegate void SavingEventHandler<T>(T ident) where T : Entity;

Saving is used tipically to assert for permission and throw an exception if necessary before any change is made in the database.

Saved

Saved is executed after all the objects in the graph are saved.

public delegate void SavedEventHandler<T>(T ident, SavedEventArgs args) where T : Entity;

Use Saved to create related entities after some entity is saved, since you already have the Id. One good example are MList<T> fields with [Ignore] attribute that are represented as an independent EntityKind.Relational entity in the database.

If you want to assert for integrity, instead of Saved, you can use a combination of Saving and Transaction PreRealCommit / PostRealCommit.

Retrieved

Retrieved is executed for each retrieved entity after a LINQ query is completely processes.

public delegate void RetrievedEventHandler<T>(T ident) where T : Entity;

Consider using ModifiableEntity.PostRetrieving instead if you have control of the entity and the changes do not require interacting with the Logic assembly.

FilterQuery

FilterQuery is processed at the early stages of the LINQ provider pipeline to allow you add filters to Database.Query<T>() and Database.MListQuery<E, V>() expressions.

public delegate FilterQueryResult<T> FilterQueryEventHandler<T>() where T : Entity;

public class FilterQueryResult<T> : IFilterQueryResult where T : Entity
{
    public readonly Expression<Func<T, bool>> InDatabaseExpresson;
    public readonly Func<T, bool> InMemoryFunction; //Optional
}

Use FilterQuery to filter all the queries implicitly, the way Authorization and Isolation module do it.

FilterQuery takes effects in all queries of the LINQ provider, including simple Database.Retrieve, UnsafeDelete, UnsafeUpdate, UnsafeInsert, etc..

When executing Database.MListQuery<E, V>(), will be automatically filtered based in the FilterQuery event of the Parent property (generic argument E).

InMemoryFunction is a function that can be executed in-memory to test for whether a object is visible or not. This is usuefull for filtering out entities in in-memory caches.

PreUnsafeDelete

PreUnsafeDelete is invoked before whenever a UnsafeDelete is executed.

public delegate void PreUnsafeDeleteHandler<T>(IQueryable<T> entityQuery);

This event is really useful for cascade deleting and cache invalidation:

Schema.Current.EntityEvents<ProjectEntity>().PreUnsafeDelete += query => 
	query.SelectMany(proj => Database.Query<BugEntity>().Where(b=>b.Project.RefersTo(proj)))
    .UnsafeDelete();

PreUnsafeMListDelete

PreUnsafeMListDelete is invoked whenever UnsafeDeleteMList is invoked for a MListTable that belongs to the entity T.

public delegate void PreUnsafeMListDeleteHandler<T>(IQueryable mlistQuery, IQueryable<T> entityQuery);

PreUnsafeUpdate

PreUnsafeUpdate is invoked whenever UnsafeUpdate is invoked in the table T or one of his MListTables that belongs to the entity T.

public delegate void PreUnsafeUpdateHandler<T>(IUpdateable update, IQueryable<T> entityQuery);

PreUnsafeInsert

PreUnsafeInsert is invoked whenever UnsafeInsert is invoked in the table T or one of his MListTables that belongs to the entity T.

public delegate void PreUnsafeInsertHandler<T>(IQueryable query, LambdaExpression constructor, IQueryable<T> entityQuery);