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Populate Created and LastModified automagically in EF Core

Looking forward to build a framework, (No repository pattern to working with DbSets directly) to autopopulate Created and last modified automatically, rather than spitting out these codes through out code base.
Could you point me out in right direction how to achieve it.
In past I tried populating these in constructors, however that seems
like a nasty code and every time we pull up somting from database EF
change tracking will mark the entity as modified.
.ctor()
{
Created = DateTime.Now;
LastModified = DateTime.Now;
}
public interface IHasCreationLastModified
{
DateTime Created { get; set; }
DateTime? LastModified { get; set; }
}
public class Account : IEntity, IHasCreationLastModified
{
public long Id { get; set; }
public DateTime Created { get; set; }
public DateTime? LastModified { get; set; }
public virtual IdentityUser IdentityUser { get; set; }
}

Starting with v2.1, EF Core provides State change events:
New Tracked And StateChanged events on ChangeTracker can be used to write logic that reacts to entities entering the DbContext or changing their state.
You can subscribe to these events from inside your DbContext constructor
ChangeTracker.Tracked += OnEntityTracked;
ChangeTracker.StateChanged += OnEntityStateChanged;
and do something like this:
void OnEntityTracked(object sender, EntityTrackedEventArgs e)
{
if (!e.FromQuery && e.Entry.State == EntityState.Added && e.Entry.Entity is IHasCreationLastModified entity)
entity.Created = DateTime.Now;
}
void OnEntityStateChanged(object sender, EntityStateChangedEventArgs e)
{
if (e.NewState == EntityState.Modified && e.Entry.Entity is IHasCreationLastModified entity)
entity.LastModified = DateTime.Now;
}

One possible solution (the one we're currently using where I work) is to override the SaveChanges() method in the DbContext and add a little bit of code to loop through changed entities setting the values
public override int SaveChanges()
{
var changedEntriesCopy = ChangeTracker.Entries()
.Where(e => e.State == EntityState.Added ||
e.State == EntityState.Modified ||
e.State == EntityState.Deleted)
.ToList();
var saveTime = DateTime.Now;
foreach (var entityEntry in changedEntriesCopy)
{
if (entityEntry.Metadata.FindProperty("Created") != null && entityEntry.Property("Created").CurrentValue == null)
{
entityEntry.Property("Created").CurrentValue = saveTime;
}
if (entityEntry.Metadata.FindProperty("Updated") != null)
{
entityEntry.Property("Updated").CurrentValue = saveTime;
}
}
return base.SaveChanges();
}
Our situation is basically set up similar to that - Created in our situation is nullable so that when a new entity is created the value is null in code up to creation (makes it easy to check if Created has been populated ever).
There may be other solutions, but this was the easiest to get set up for us, and hasnt had any noticeable performance impact

How to set navigation property in Entity Framework 6 in case of generic entities

I have update a generic update method as follows
public virtual void Update<TEntity>(TEntity entity, string modifiedBy =
null) where TEntity : class,IEntity
{
using (var context = new BanyanDbContext())
{
entity.ModifiedDate = DateTime.UtcNow;
entity.ModifiedBy = modifiedBy;
var existingEntiy = context.Set<TEntity>().Find(entity.Id);
context.Entry(existingEntiy).CurrentValues.SetValues(entity);
context.Entry(existingEntiy).State = EntityState.Modified;
Save(context);
}
}
This method is working fine for updating non reference type values, but CurrentValues.SetValues() does not set or update navigation properties.
How can I set navigation property in this scenario.

public TEntity RemoveNavigationProperties(TEntity input)
{
foreach (var item in input.GetType().GetProperties().Where(x => x.PropertyType.Namespace == input.GetType().Namespace))
{
item.SetValue(input, null);
}
return input;
}
This worked for me. (I just needed to null them)

Adding Mutliple Row Effected properly but not Updating (C#, Entity Framework 6)

As you can see below, I'm trying to update the "active" and "version" fields, which are properties of the templateData object.
When I want to add a new record, it works fine and meets the needs. But when I try to update the state.modified line, the error is:
Attaching an entity of type '...' failed because another entity already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate.
Although I have tried many ways of crashing (as you noticed) I have not been successful.
What is the cause of this error? And how can I handle it?
Thank you for your help.
Service:
public ResultObject<TemplateData> SaveTemplateData(TemplateData oTemplateData)
{
var oResult = new ResultObject<TemplateData>();
using (var contextTransaction = _context.Database.BeginTransaction())
{
try
{
var listTempDatas = _context.TemplateDatas.Where(td => td.TemplateRID == oTemplateData.TemplateRID)
.ToList();
#region active/version
oTemplateData.Active = true;
if (listTempDatas.Count > 0)
{
#region resetActives
listTempDatas.ForEach(ltd => ltd.Active = false);
#endregion
#region getMaxVersion
var maxVersionValue = listTempDatas.Max(ltd => ltd.TemplateVersion);
//var maxVersionValue2 = listTempDatas.OrderByDescending(ltd => ltd.TemplateVersion).Select(ltd => ltd.TemplateVersion).First();
oTemplateData.TemplateVersion = maxVersionValue + 1;
#endregion
}
else if (listTempDatas.Count == 0)
{
oTemplateData.TemplateVersion = 1;
}
#endregion
if (oTemplateData.ID > 0)
{
var oldTempData = _context.TemplateDatas.AsNoTracking()
.FirstOrDefault(td => td.ID == oTemplateData.ID);
if (oldTempData != null)
_context.Entry(oTemplateData).State = EntityState.Modified;// and there it is
}
else if (oTemplateData.ID == 0)
{
_context.Entry(oTemplateData).State = EntityState.Added;
}
_context.SaveChanges();
oResult.ResulObject = oTemplateData;
contextTransaction.Commit();
}
catch (Exception e)
{
contextTransaction.Rollback();
oResult.AddError("TemplateService.SaveTemplateData", e.ToString());
}
}
return oResult;
}
Entity:
public class TemplateData
{
...
public int ID { get; set; }
public int? TemplateRID { get; set; }
...
public int? TemplateVersion { get; set; }
public bool? Active { get; set; }
...
public virtual Template Template { get; set; }
}
DataContextExtension:
public static ApplicationDbContext BulkInsert<T>(this ApplicationDbContext context, T entity, int count,
int batchSize) where T : class
{
context.Set<T>().Add(entity);
if (count % batchSize == 0)
{
context.SaveChanges();
context.Dispose();
context = new ApplicationDbContext();
// This is optional
context.Configuration.AutoDetectChangesEnabled = false;
}
return context;
}

The problem is that the line
var listTempDatas = _context.TemplateDatas.Where(td => td.TemplateRID == oTemplateData.TemplateRID)
.ToList();
already loads (tracks) in the context the existing entity you are trying to update.
So first you can try to find it in that list (instead of with a separate database query):
var oldTempData = listTempDatas.FirstOrDefault(td => td.ID == oTemplateData.ID);
and then simply update the properties of the existing entity rather than trying to mark the detached entity as modified:
if (oldTempData != null)
_context.Entry(oldTempData).CurrentValues.SetValues(oTemplateData); // and there you go

Entity Framework - Many to Many relationship not saving to database

I have stumbled upon a problem with Entity Framework this morning.
I have following code mapping a modified entity and saving it into database.
public Group Save(Group x)
{
using (var db = new HostContext())
{
db.Projects.Attach(x.Project);
if (x.ID != 0)
{
db.AttachableObjects.Attach(x);
var manager = ((IObjectContextAdapter)db).ObjectContext.ObjectStateManager;
manager.ChangeObjectState(x, EntityState.Modified);
}
else
{
db.AttachableObjects.Add(x);
}
db.SaveChanges();
return x;
}
}
I call Save method with existing group as a parameter. Group contains one user I want to add as a member.
The method finishes successfully, however the relationship is not persisted in database.
Any help is very appreciated.
EDIT: These are my classes
class User : AttachableObject
{
...
private List<Group> memberof;
[DataMember]
[InverseProperty("Members")]
public List<Group> MemberOf
{
get { return memberof; }
set { memberof = value; }
}
...
}
class Group : AttachableObject
{
...
private List<User> members;
[DataMember]
[InverseProperty("MemberOf")]
public List<User> Members
{
get { return members; }
set { members = value; }
}
...
}
EDIT2: This is where the Save method is called
public Group AcceptInvite(int id)
{
var mapper = new InviteMapper();
var userMapper = new UserMapper();
var groupMapper = new GroupMapper();
var invite = mapper.Find(id);
if (invite != null)
{
var group = groupMapper.Find(invite.GroupID);
var user = userMapper.Find(invite.InviteeID);
group.Members.Add(user);
mapper.Delete(invite.ID);
return groupMapper.Save(group);
}
return null;
}
EDIT3: My mappers
public class GroupMapper
{
public Group Find(int id)
{
using (var db = new HostContext())
{
return db.AttachableObjects
.Include("Project")
.OfType<Group>().FirstOrDefault(x => x.ID == id);
}
}
}
The rest of the mappers is the same, only using their own tables.

You are not changing the relationship info of Project, you are only setting x to modified, relationship info must be changed explicitly.
So x.Project must have some property that points back to Group, you need to set it so the change is recorded.
I am guessing that x is resurrected via some deserialization process?

Save detached object graph using Entity Framework code first causes Primary Key violation

I'm trying to save an object graph of POCOs I have mapped to EF6 using Code First fluent notations.
Upon saving the object graph however, I stumble upon primary key violation exceptions.
The object graph is quite simple:
One Issue can contain multiple WorkItems with each one Author (as User).
The objects are populated externally (using a Web API)
When I attempt to save an issue with two workitems which refer to the same author, I would expect the issue to be inserted, the workitems to be inserted and one author to be inserted, and the other one to be referenced or be updated.
What happens however is that the issue is inserted, the workitems are inserted and both references to the same user are inserted, resulting in a primary key violation.
Simplified Issue object:
public class Issue
{
public Issue()
{
WorkItems = new List<WorkItem>();
}
public string Id { get; set; }
private List<WorkItem> _workItems;
public List<WorkItem> WorkItems
{
get { return _workItems ?? new List<WorkItem>(); }
set { _workItems = value; }
}
}
Simplified WorkItem:
public class WorkItem
{
public string Id { get; set; }
public string AuthorLogin
{
get; set;
}
private WorkItemAuthor _author;
public WorkItemAuthor Author
{
get { return _author; }
set { _author = value;
if (value != null)
{
AuthorLogin = value.Login;
}
else
{
AuthorLogin = string.Empty;
}
}
}
}
Simplified user object:
public class User
{
public string Login { get; set; }
public string FullName { get; set; }
}
Their Code-first configurations:
internal IssueConfiguration()
{
HasKey(x => x.Id);
HasMany(x => x.WorkItems);
}
internal WorkItemConfiguration()
{
HasKey(x => x.Id);
HasRequired(p => p.Author)
.WithMany(b => b.WorkItems)
.HasForeignKey(x=>x.AuthorLogin);
}
internal UsersConfiguration()
{
HasKey(x => x.Login);
}
All quite straightforward. Upon database create, de tables look fine and dandy too, with FKs on the columns where one would expect them
Now when saving the issue, it would have been nice if the object graph would be inserted, and the reference to existing objects would be recognized automagically and optionally inserted or referenced only.
I attempt to add issues accordingly:
using (var db = new Cache.Context())
{
if (db.Issues.Any(e => e.Id == issue.Id))
{
db.Issues.Attach(issue);
db.Entry(issue).State = EntityState.Modified;
}
else
{
db.Issues.Add(issue);
}
db.SaveChanges();
}
Is the solution to this issue that I walk through the object graph to manually add or attach the other objects in the graph too? I would expect by defining the proper Foreign Key values these references would be recognized.

I finally ended up doing something similar to this, quite laborious and I would still like to find a better way.
Finding out whether an entity is already attached or exists in the database turned out to be pollute the model too much (implementing IEquatable<T> is fine, but I think implementing IEntityWithKey on my POCOs pollutes the POCO too much. (and till that did not seem to suffice tracking entities in the context)
internal static void Save(this List<Issue> issues)
{
using (var db = new Context())
{
foreach (var issue in issues.ToList())
{
foreach (var workItem in issue.WorkItems.ToList())
{
if (workItem.Author != null)
{
var existing = db.Users.SingleOrDefault(e => e.Login == workItem.Author.Login);
if (existing == null)
{
db.Users.Add(workItem.Author);
}
else
{
//Update existing entities' properties
existing.Url = workItem.Author.Url;
//Replace reference
workItem.Author = existing;
}
db.SaveChanges();
}
var existingWorkItem = db.WorkItems.SingleOrDefault(e => e.Id == workItem.Id);
if (existingWorkItem == null)
{
db.WorkItems.Add(workItem);
}
else
{
//Update existing entities' properties
existingWorkItem.Duration = workItem.Duration;
//Replace reference
issue.WorkItems.Remove(workItem);
issue.WorkItems.Add(existingWorkItem);
}
db.SaveChanges();
}
var existingIssue = db.Issues.SingleOrDefault(x => x.Id == issue.Id);
if (existingIssue == null)
{
db.Issues.Add(issue);
}
else
{
//Update existing entities' properties
existingIssue.SpentTime = issue.SpentTime;
}
db.SaveChanges();
}
}
}

There is a small bug in the Issue object.
"return _workItems ?? new List();" could return a new WorkItem on every get if _workItems ever became null. Here is the fixed version.
public class Issue {
public Issue() {
WorkItems = new List<WorkItem>();
}
public String Id {
get; set;
}
public List<WorkItem> WorkItems { get; private set; }
}