EF Core 中断开连接的实体

Question

I have been looking to log changes on entities in a disconnected scenario.

Original Problem: I call DbContext.Update(Entity) on an updated complex entity and even though nothing has changed, everything is marked as Changed by the ChangeTracker and my concurrency RowVersion column counts up.

POST User with no changes

"userSubPermissions": [],
"fidAdresseNavigation": {
    "idAdresse": 1,
    "fidPlzOrt": 3,
    "strasse": "Gerold Str.",
    "hausnr": "45",
    "rowVersion": 10,
    "isDeleted": 0,
    "fidPlzOrtNavigation": {
        "idPlzOrt": 3,
        "plz": "52062",
        "ort": "Aachen",
        "rowVersion": 9,
        "isDeleted": 0
    }
},
"idUser": 35,
"fidAnrede": null,
"fidAdresse": 1,
"fidAspnetuser": "a7ab78be-859f-4735-acd1-f06cd832be7e",
"vorname": "Max",
"nachmname": "Leckermann",
"eMail": "kunde@leasing.de",
"rowVersion": 11,
"isDeleted": 0

POST Returned user

"userSubPermissions": [],
"fidAdresseNavigation": {
    "idAdresse": 1,
    "fidPlzOrt": 3,
    "strasse": "GeroldPenis Str.",
    "hausnr": "45",
    "rowVersion": 11,
    "isDeleted": 0,
    "fidPlzOrtNavigation": {
        "idPlzOrt": 3,
        "plz": "52062",
        "ort": "Aachen",
        "rowVersion": 10,
        "isDeleted": 0
    }
},
"idUser": 35,
"fidAnrede": null,
"fidAdresse": 1,
"fidAspnetuser": "a7ab78be-859f-4735-acd1-f06cd832be7e",
"vorname": "Max",
"nachmname": "Leckermann",
"eMail": "kunde@leasing.de",
"rowVersion": 12,
"isDeleted": 0

The RowVersion logic is in the DBContext and only changes the row version when the Entity State is Modified.

foreach (var entity in ChangeTracker.Entries().Where(e => e.State == EntityState.Modified))
        {
            var saveEntity = entity.Entity as ISavingChanges;
            saveEntity.OnSavingChanges();
        }

From my investigation over the past 2 days there seem to be two alternatives for EF Core.

1.- As mentioned on this and many similar posts you can use the TrackGraph https://www.mikesdotnetting.com/article/303/entity-framework-core-trackgraph-for-disconnected-data

Problem: This solution marks the entire entity as changed when the ID of the entity is present even though nothing has changed. I get the exact same result as described above, the RowVersion counts up meaning my Entities an all of its Properties have been marked as Modified.

2.- As mentioned in this post https://blog.tonysneed.com/2017/10/01/trackable-entities-for-ef-core/ you can download a NuGet package and implement the IMergeable and the ITrackable interfaces on my Entities.

Problem: The Client needs to track the changes in the Model and pass them to the API, which I want to avoid since Angular does not seem to offer a good solution for this.

3.- There is another solution in the book Programming Entity Framework on how EF 6 handles disconnected scenarios, by recording original values Chapter 4: Recording Original Values . When an Update comes in, the context reads the entity from the DB and then compares the incoming Entity with the DB Entity to see if any changes have been made on the properties and then marks them as Modified.

https://www.oreilly.com/library/view/programming-entity-framework/9781449331825/ch04.html

Problem: Some of the code described in the book is not implementable in EF Core one example is.

((IObjectContextAdapter)this).ObjectContext
.ObjectMaterialized += (sender, args) =>
{
  var entity = args.Entity as IObjectWithState;
  if (entity != null)
  {
    entity.State = State.Unchanged;

    entity.OriginalValues =
      BuildOriginalValues(this.Entry(entity).OriginalValues);
  }
};

There must be a way to implement this clever solution of handling changes on the API instead of the Client in Disconnected scenarios, otherwise, this might be a very useful Feature to have in EF Core since most Developers are using it for Disconnected scenarios.

Answer 1

My response is using TrackGraph

Synopsis

I want to Modify only few columns of the entity as well as Add\Modify nested child entities

• Here, I am updating Scenario entity and modifying only ScenarioDate .
• In its child entity, ie navigation property TempScenario , I am adding a new record
• In the nested child entity, Scenariostation , I am adding as well modifying the records

public partial class Scenario
{
    public Scenario()
    {
        InverseTempscenario = new HashSet<Scenario>();
        Scenariostation = new HashSet<Scenariostation>();
    }
    public int Scenarioid { get; set; }
    public string Scenarioname { get; set; }
    public DateTime? Scenariodate { get; set; }
    public int Streetlayerid { get; set; }
    public string Scenarionotes { get; set; }
    public int? Modifiedbyuserid { get; set; }
    public DateTime? Modifieddate { get; set; }
    public int? Tempscenarioid { get; set; }

    
    public virtual Scenario Tempscenario { get; set; }
    public virtual ICollection<Scenario> InverseTempscenario { get; set; }
    public virtual ICollection<Scenariostation> Scenariostation { get; set; }
}


public partial class Scenariostation
{
    public Scenariostation()
    {
        Scenariounit = new HashSet<Scenariounit>();
    }

    public int Scenariostationid { get; set; }
    public int Scenarioid { get; set; }
    public int Stationid { get; set; }
    public bool? Isapplicable { get; set; }
    public int? Createdbyuserid { get; set; }
    public int? Modifiedbyuserid { get; set; }
    public DateTime? Modifieddate { get; set; }
    
    public virtual Scenario Scenario { get; set; }
    public virtual Station Station { get; set; }
}

public partial class Station
{
    public Station()
    {
        Scenariostation = new HashSet<Scenariostation>();
    }

    public int Stationid { get; set; }
    public string Stationname { get; set; }
    public string Address { get; set; }
    public NpgsqlPoint? Stationlocation { get; set; }
    public int? Modifiedbyuserid { get; set; }
    public DateTime? Modifieddate { get; set; }

    public virtual ICollection<Scenariostation> Scenariostation { get; set; }
}

• With EF Core, data update in a disconnected scenario is tricky if you don't want to make 2 database round trips.

• Even though 2 database trips seems not significant, it can hamper performance if the data table has millions of records.

• Also, if there are only few columns to be updated, including columns of nested child entities, Usual Approach will not work

Usual approach

public virtual void Update(T entity)
{
    if (entity == null)
        throw new ArgumentNullException("entity");

    var returnEntity = _dbSet.Attach(entity);
    _context.Entry(entity).State = EntityState.Modified;
}

But the problem here for a disconnected EF Core update, if you use this DbContext.Entry(entity).EntityState = EntityState.IsModified , all the columns will updated. and so some columns will be updated to its default value ie null or default data type value.

Further more, some records of ScenarioStation won't be updated at all because the entity state will be UnChanged .

So inorder to update only the columns which are sent from the client, somehow EF Core needs to be told .

Using ChangeTracker.TrackGraph

Recently I found this DbConetxt.ChangeTracker.TrackGraph method which can be used to mark Added , UnChanged state for the entities.

difference is that with TrackGraph , you can add custom logic, as it iteratively navigates through Navigation properties of the entity.

My custom logic using TrackGraph

public virtual void UpdateThroughGraph(T entity, Dictionary<string, List<string>> columnsToBeUpdated)
{
    if (entity == null)
        throw new ArgumentNullException("entity");

    _context.ChangeTracker.TrackGraph(entity, e =>
    {
        string navigationPropertyName = e.Entry.Entity.GetType().Name;

        if (e.Entry.IsKeySet)
        {
            e.Entry.State = EntityState.Unchanged;
            e.Entry.Property("Modifieddate").CurrentValue = DateTime.Now;

            if (columnsToBeUpdated.ContainsKey(navigationPropertyName))
            {
                foreach (var property in e.Entry.Properties)
                {
                    if (columnsToBeUpdated[e.Entry.Entity.GetType().Name].Contains(property.Metadata.Name))
                    {
                        property.IsModified = true;
                    }
                }
            }
        }
        else
        {
            e.Entry.State = EntityState.Added;
        }

    });

}

With this approach, I am able to easily handle only required column updates as well as new additions/modifications for any of the nested child entities and its columns.