Entity Framework Change Tracker Discover How to Use all Entity State
By default, Entity Framework tracks changes of the loaded entities during the life-time of the context.
- The Change Tracking tracks changes when you add new records, update or delete the existing records.
- These track changes are lost if they are not saved before the DbContext object is destroyed.
- The entity must have a primary key property to be tracked by the context.
The DbChangeTracker class gives you all the information about current entities being tracked by the context, and all the changes are kept by the DbContext level.
private static void DisplayTrackedEntities(DbChangeTracker changeTracker) { var entries = changeTracker.Entries(); foreach (var entry in entries) { Console.WriteLine("Entity Name: {0}", entry.Entity.GetType().FullName); Console.WriteLine("Status: {0}", entry.State); } }
The Change Tracker tracks an entity using any of the following states:
- Added
- Modified
- Deleted
- Unchanged
- Detached
Added State
The entity is being tracked by the context but does not yet exist in the database. If a new entity or entities are added into the context using Add() method, then it will be marked as Added.
The following example shows the tracking of newly added author entity.
using (var context = new BookStore()) { Console.WriteLine("Adding Author"); Author author = new Author() { Name = "Mark" }; context.Authors.Add(author); Console.WriteLine("Context tracking changes of {0} entities.", context.ChangeTracker.Entries().Count()); DisplayTrackedEntities(context.ChangeTracker); }
Modified State
The following example shows the tracking of an updated author entity.
using (var context = new BookStore()) { Console.WriteLine("Update Author"); Author author = context.Authors .FirstOrDefault(); author.Name = "Russell"; Console.WriteLine("Context tracking changes of {0} entities.", context.ChangeTracker.Entries().Count()); DisplayTrackedEntities(context.ChangeTracker); }
Deleted State
The following example shows the tracking of deleted author entity.
using (var context = new BookStore()) { Console.WriteLine("Delete Author"); Author author = context.Authors .FirstOrDefault(); context.Authors.Remove(author); Console.WriteLine("Context tracking changes of {0} entities.", context.ChangeTracker.Entries().Count()); DisplayTrackedEntities(context.ChangeTracker); }
Unchanged State
The following example shows the tracking of Unchanged author entity.
using (var context = new BookStore()) { Author author = context.Authors .FirstOrDefault(); Console.WriteLine("Context tracking changes of {0} entities.", context.ChangeTracker.Entries().Count()); DisplayTrackedEntities(context.ChangeTracker); }
Detached State
The following example shows the tracking of deleted author entity.
Author author;
using(var context = new BookStore())
{
author = context.Authors
.FirstOrDefault();
}
using (var context = new BookStore())
{
Console.Write(context.Entry(author).State);
}
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