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Entity Framework Core 2.0 Many to Many Inserts before primary key is generated

I'm trying to create an entity object that has many to many relationships with other entities. The relationships are indicated as follows.
public class Change {
// Change Form Fields
[Key]
[DatabaseGenerated(DatabaseGeneratedOption.Identity)]
public int ChangeId { get; set; }
public string ChangeTitle { get; set; }
public string ChangeType { get; set; }
public DateTime DateSubmitted { get; set; }
public DateTime TargetDate { get; set; }
//Many to Many Collections
public virtual ICollection<Change_CriticalBankingApp> Change_CriticalBankingApps { get; set; } = new List<Change_CriticalBankingApp>();
public virtual ICollection<Change_ImpactedBusiness> Change_ImpactedBusinesses { get; set; } = new List<Change_ImpactedBusiness>();
public virtual ICollection<Change_ImpactedService> Change_ImpactedServices { get; set; } = new List<Change_ImpactedService>();
public virtual ICollection<Change_TestStage> Change_TestStages { get; set; } = new List<Change_TestStage>();
public virtual ICollection<Change_TypeOfChange> Change_TypeOfChanges { get; set; } = new List<Change_TypeOfChange>();
And the DbContext set up is as follows
public class ChangeContext : DbContext {
public ChangeContext(DbContextOptions<ChangeContext> options) : base(options) {
Database.Migrate();
}
public DbSet<Change> Change { get; set; }
public DbSet<TestStage> TestStage { get; set; }
public DbSet<TypeOfChange> TypeOfChange { get; set; }
public DbSet<CriticalBankingApp> CriticalBankingApp { get; set; }
public DbSet<ImpactedBusiness> ImpactedBusiness { get; set; }
public DbSet<ImpactedService> ImpactedService { get; set; }
protected override void OnModelCreating(ModelBuilder modelBuilder) {
modelBuilder.Entity<Change_CriticalBankingApp>().HasKey(t => new { t.ChangeId, t.CriticalBankingAppId });
modelBuilder.Entity<Change_ImpactedBusiness>().HasKey(t => new { t.ChangeId, t.ImpactedBusinessId });
modelBuilder.Entity<Change_ImpactedService>().HasKey(t => new { t.ChangeId, t.ImpactedServiceId });
modelBuilder.Entity<Change_TestStage>().HasKey(t => new { t.ChangeId, t.TestStageId });
modelBuilder.Entity<Change_TypeOfChange>().HasKey(t => new { t.ChangeId, t.TypeOfChangeId });
}
}
Where I start running into problems is I'm not generating an Id using Entity Framework, the primary key is an identity in SQL Server 2012 and I get that back once the insert is completed, as opposed to using a GUID (which I've read pretty much everywhere is super frowned upon in the DBA world).
So what ends up happening is I either try and do the insert and it tries to insert the many to many relationships with changeId in the junction table being null (because it isn't generated yet) or when I try what I have below to do an insert and an update in one post method. It errors out because the ChangeId key value is already being tracked. Here is what I'm attempting below.
Controller method
public IActionResult CreateChange([FromBody] ChangeModel change) {
if (change == null) {
return BadRequest();
}
//Remove many to many from Change to insert without them (as this can't be done until primary key is generated.
List<Change_CriticalBankingAppModel> criticalApps = new List<Change_CriticalBankingAppModel>();
criticalApps.AddRange(change.Change_CriticalBankingApps);
List<Change_ImpactedBusinessModel> impactedBusinesses = new List<Change_ImpactedBusinessModel>();
impactedBusinesses.AddRange(change.Change_ImpactedBusinesses);
List<Change_ImpactedServiceModel> impactedServices = new List<Change_ImpactedServiceModel>();
impactedServices.AddRange(change.Change_ImpactedServices);
List<Change_TestStageModel> testStages = new List<Change_TestStageModel>();
testStages.AddRange(change.Change_TestStages);
List<Change_TypeOfChangeModel> changeTypes = new List<Change_TypeOfChangeModel>();
changeTypes.AddRange(change.Change_TypeOfChanges);
change.Change_CriticalBankingApps.Clear();
change.Change_ImpactedBusinesses.Clear();
change.Change_ImpactedServices.Clear();
change.Change_TestStages.Clear();
change.Change_TypeOfChanges.Clear();
//Map Change model to change entity for inserting
var changeEntity = Mapper.Map<Change>(change);
_changeRepository.AddChange(changeEntity);
if (!_changeRepository.Save()) {
throw new Exception("Creating change failed on save.");
}
var changetoReturn = Mapper.Map<ChangeModel>(changeEntity);
//Iterate through Many to many Lists to add generated changeId
foreach (var criticalApp in criticalApps) {
criticalApp.ChangeId = changetoReturn.ChangeId;
}
foreach (var impactedBusiness in impactedBusinesses) {
impactedBusiness.ChangeId = changetoReturn.ChangeId;
}
foreach (var impactedService in impactedServices) {
impactedService.ChangeId = changetoReturn.ChangeId;
}
foreach (var testStage in testStages) {
testStage.ChangeId = changetoReturn.ChangeId;
}
foreach (var changeType in changeTypes) {
changeType.ChangeId = changetoReturn.ChangeId;
}
//Add many to many lists back to change to update
changetoReturn.Change_CriticalBankingApps = criticalApps;
changetoReturn.Change_ImpactedBusinesses = impactedBusinesses;
changetoReturn.Change_ImpactedServices = impactedServices;
changetoReturn.Change_TestStages = testStages;
changetoReturn.Change_TypeOfChanges = changeTypes;
changeEntity = Mapper.Map<Change>(changetoReturn);
_changeRepository.UpdateChange(changeEntity);
if (!_changeRepository.Save()) {
throw new Exception("Updating change with many to many relationships failed on save.");
}
changetoReturn = Mapper.Map<ChangeModel>(changeEntity);
return CreatedAtRoute("GetChange",
new { changeId = changetoReturn.ChangeId },
changetoReturn);
}
Relevant Repository methods
public Change GetChange(int changeId) {
return _context.Change.FirstOrDefault(c => c.ChangeId == changeId);
}
public void AddChange(Change change) {
_context.Change.Add(change);
}
public void UpdateChange(Change change) {
_context.Change.Update(change);
}
public bool ChangeExists(int changeId) {
return _context.Change.Any(c => c.ChangeId == changeId);
}
I encounter this error on the update attempt.
I understand that if I were to have entity framework generate the guid instead of having the database generate the identity int that I would have a much easier time with this but a requirement for this project is to not use Guid's.
Any help on how to successfully process this would be greatly appreciated.
EDIT: In case it helps, here is the http post I'm using with postman.
{
"changeTitle": "Test",
"changeType": "Test",
"dateSubmitted": "02/12/2018",
"targetDate": "02/12/2018",
"change_CriticalBankingApps": [
{
"criticalBankingAppId" : 1,
"description" : "Very critical"
},
{
"criticalBankingAppId" : 2,
"description" : "Moderately critical"
}
],
"change_impactedBusinesses": [
{
"ImpactedBusinessId" : 1
},
{
"ImpactedBusinessId" : 2
}
]
}

The error you are getting has nothing to do with the guid vs db identity.
You are getting it because you are:
Fetching an entity from the database
Creating new entity (not tracked) from within your controller (the mapper does this)
Try to update the entity that is not tracked by entity framework
The update will try to add the entity to the EF repository, but will fail because it already contains an entity with the given ID.
If you plan to make changes to an entity, you need to make sure entity framework tracks the entity prior to calling the update method.
If EF does not track your entity, it does not know which fields have been updated (if any).
Edit:
If you want to get rid of the error, you could detach your original entity. Make sure you do it prior to mapping the changetoReturn back into your changeEntity.
dbContext.Entry(entity).State = EntityState.Detached;
But since your new entity won't be tracked, I don't think anything will be updated (EF does not know what has been changed).
Edit 2:
Also take a look at this to get your changes back into your original entity.
Change this:
changeEntity = Mapper.Map<Change>(changetoReturn);
Into this:
Mapper.Map(changetoReturn, changeEntity);
Using Automapper to update an existing Entity POCO

add new entities via joint table...that way, entities are tracked both in the joint table and their individual respective tables

Ok, whether this is an elegant solution is up for debate, but I was able to detach the entity state from changeEntity after doing the initial insert as follows
_changeRepository.AddChange(changeEntity);
_changecontext.Entry(changeEntity).State = EntityState.Detached;
Then after reattaching all of the many to many lists back to changeToReturn, I created a new Change entity and added that entity state, and updated on that as follows.
var newChangeEntity = Mapper.Map<Change>(changeToReturn);
_changecontext.Entry(newChangeEntity).State = EntityState.Added;
_changeRepository.UpdateChange(newChangeEntity);
Then I returned this mapped back to a view model.
It seems hacky and perhaps through a deeper understanding of entity framework I'll discover a much better way of going about this but this works for now.

Entity Framework in disconnected scenario throws saving or accepting changes failed because more than one entity of type

I am working in a small project using Web API, and entity Framework. And I facing some issue in posting my entity.
My entities look like this:
public class DayExercises
{
public DayExercises()
{
Exercises = new List<Exercise>();
}
[Key]
public int Id { get; set; }
public string Day { get; set; }
public virtual ICollection<Exercise> Exercises { get; set; }
}
and my Exercise entity look like this.
public class Exercise
{
public Exercise()
{
DayExercises = new List<DayExercises>();
}
public int Id { get; set; }
public string Name { get; set; }
public virtual List<DayExercises> DayExercises { get; set; }
}
and my web api method for posting the dayExercises look like this
[ResponseType(typeof(WorkoutTemplate))]
public IHttpActionResult PostWorkoutTemplate(DayExercises dayExercises)
{
if (!ModelState.IsValid)
{
return BadRequest(ModelState);
}
foreach (var dayExercise in dayExercises)
{
fitnessDbContext.Entry(dayExercise).State = EntityState.Added;
foreach (var exercise in dayExercise.Exercises.ToList())
{
fitnessDbContext.Entry(exercise).State = EntityState.Unchanged;
}
}
db.SaveChanges();
return CreatedAtRoute("DefaultApi", new { id = dayExercises.Id }, dayExercises);
}
The relationship is Many-To-Many.
Problem:
I am sending a dayExercise with existing Exercise(already existing in database) to my method. but when I'm posting dayExercise with SAME two exercises. it throw that exception:
Additional information: Saving or accepting changes failed because more than one entity of type 'FitnessFirst.WebApi.Exercise' have the same primary key value.
Ensure that explicitly set primary key values are unique. Ensure that database-generated primary keys are configured correctly in the database and in the Entity Framework model.
Use the Entity Designer for Database First/Model First configuration. Use the 'HasDatabaseGeneratedOption" fluent API or 'DatabaseGeneratedAttribute' for Code First configuration.
I also tried to Deattach the entities, and Get the exercise from Database using their ID and Attach them again and add it to the dayExercise but it doesn't save to database.
NOTE: when I add two different exercises, it doesn't throw that Exception.
I also read the following answers, but it doesn't solve it: Ensure that explicitly set primary key values are unique
Any Suggestion or explanation.

I know this is an old post, but I ran into the same issue yesterday. This is the solution I came up with. Basically entity framework change tracker only allows unique values for an entity. So to get around the error you need to check if the entity already exists in the change tracker and use that instance.
var excercises = dayExercise.Exercises.ToList();
for (int i = 0; i < excercises.Count; i++)
{
var unchangedEntity = _dbContext.ChangeTracker.Entries<Exercise>()
.Where(xy => xy.State == EntityState.Unchanged &&
xy.Entity.Id == excercises [i].Id).FirstOrDefault();
if (unchangedEntity == null)
{
fitnessDbContext.Entry(excercises[i]).State = EntityState.Unchanged;
}
else
{
excercises[i] = unchangedEntity.Entity;
}
}

How to manually set entity primary key in Entity Framework code first database?

Well, I have the following model structure: I have one class - DatabaseEntity which is basically
public class DatabaseEntity
{
public int Id { get; set; }
}
so each entity like product, category etc will inherit DatabaseEntity and have Id property. Also I have typical EntityFramework repository class with InsertOrUpdate method:
private readonly DbContext _database;
public void InsertOrUpdate<TObject>(TObject entity) where TObject : DatabaseEntity
{
if(entity.Id == default(int))
{
// New entity
DbSet<TObject>().Add(entity);
}
else
{
// Existing entity
_database.Entry(entity).State = EntityState.Modified;
}
_database.SaveChanges();
}
Then I download from eBay via eBay api list of categoies I have to add to database. Basically category is:
public class EbayCategory : DatabaseEntity
{
// It has Id since it inherits DatabaseEntity
public string Name { get; set; }
// ... some other properties
}
But, the problem is, when I download those categories I download and their Id properties, which, of course, already have values. And when I try to save them to database like:
public void UpdateCategories(IEnumerable<EbayCategory> newCategories)
{
foreach (var newCategory in newCategories)
{
_repository.InsertOrUpdate(newCategory);
}
}
I face some issues... First of all, entity.Id != default(int) because it has value, so repository tries to update this entity, instead of adding, but it is not in the database or context so it throws the following exception:
System.Data.Entity.Infrastructure.DbUpdateConcurencyException
"Store update, insert, or delete statement affected an unexpected number of rows (0). Entities may have been modified or deleted since entities were loaded. Refresh ObjectStateManager entries."
... because it thinks that someone else deleted entity which I am trying to update. How can I save this InsertOrUpdate logic, since a lot of projects are based on it, and be able to add items (EbayCategories) with primary key (Id) to database and then update/delete them like other entities without discarding EbayCategory.Id value?

To allow you to manually generate Ids you need a class that has a manually generated ID - so it cannot inherit from DatabaseEntity
public class EbayCategory
{
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public int Id { get; set; }
public string Name { get; set; }
// ... some other properties
}
Now you will need a different InsertOrUpdate to handle entities that have manually generated keys:
public void InsertOrUpdate(EbayCategory entity)
{
if(Find(entity.ID == null)
{
// New entity
DbSet<EbayCategory>().Add(entity);
}
else
{
// Existing entity
_database.Entry(entity).State = EntityState.Modified;
}
_database.SaveChanges();
}

Colin's answer above quite correctly shows how to achieve this setting using data annotations.
But in the presented problem the entity is a subclass so you can't add the annotation without changing the entity class.
There is an alternative configuration method: Fluent Configuration. Here's my example using an EntityTypeConfiguration class:
public class LookupSchoolsConfiguration : EntityTypeConfiguration<LookupSchools>
{
public LookupSchoolsConfiguration()
{
Property(l => l.Id).HasDatabaseGeneratedOption(DatabaseGeneratedOption.None);
}
}
You can also add configuration directly to the modelBuilder as per this post: https://stackoverflow.com/a/4999894/486028

Cannot update many-to-many relationships in Entity Framework

I am using Entity Framework 4.3 Code First, and I have problem with updating many-to-many relationships.
I defined the following classes:
public abstract class Entity
{
[Column(Order = 0)]
[Key]
public int Id { get; set; }
[Timestamp]
[Column(Order = 1)]
public byte[] Version { get; set; }
}
public class Video : Entity
{
public string Title { get; set; }
public string Description { get; set; }
public TimeSpan Length { get; set; }
public virtual ICollection<Coworker> Coworkers { get; set; }
}
public class Coworker : Entity
{
public string FirstName { get; set; }
public string LastName { get; set; }
public virtual ICollection<Video> Videos { get; set; }
}
When the database is created, the schema look right:
There is a Videos, Coworkers and VideoCoworkers table too, without
I use repository pattern in an N-Tier application to access database, my Insert and Update method looks like this:
public T Insert(T entity)
{
//Creates database context. When it disposes, it calls context.SaveChanges()
using (var session = new DatabaseSession())
{
session.Context.Set<T>().Add(entity);
}
}
public T Update(T entity)
{
//Creates database context. When it disposes, it calls context.SaveChanges()
using (var session = new DatabaseSession())
{
entity = session.Context.Set<T>().Attach(entity);
session.Context.Entry(entity).State = EntityState.Modified;
}
return entity;
}
When I update an entity, I create the entity object from a DTO, that's why use DbSet.Attach instead of selecting it and updating the properties one-by-one.
When I initialize the database, I add some test data:
Create 3 Coworkers, where I set first and last name. (A, B, C)
Create 3 Videos, where I set title, description and length, and also set some coworkers. First video has A,B, second has B,C and third has A,C.
When I list the Videos from code, I can see that Video.Coworkers collection is filled with good values, and when I query the link table (VideoCoworkers) in SQL Server Management Studio, it also looks good.
My problem is
when I update for example the title of the Video, it works. But when I try to delete from Video2 the existing coworkers (B and C), and try to add coworker A, then the relationship is not updated. It also does not work when I only try to add new coworker, or only try to delete one. I create the entity which is used as the parameter of the Update() method by creating a new Video entity with a new collection of Coworkers (which are selected from the database with Find() method by Id).
What is the correct way to update many-to-many relationships?

But when I try to delete from Video2 the existing coworkers (B and C),
and try to add coworker A, then the relationship is not updated.
Without using a generic repository the correct procedure would be:
using (var session = new DatabaseSession())
{
video2 = session.Context.Set<Video>().Include(v => v.Coworkers)
.Single(v => v.Id == video2Id);
coworkerA = new Coworker { Id = coworkerAId };
session.Context.Set<Coworker>().Attach(coworkerA);
video2.Coworkers.Clear();
video2.Coworkers.Add(coworkerA)
session.Context.SaveChanges();
}
The essential part is that you must load or attach the entity in its original state, change the entity, i.e. remove and add children, and then save the changes. EF's change detection will create the necessary INSERT and DELETE statements for the link table entries. The simple procedure to set the state to Modified you are trying in your generic Update method is suited only for updating scalar properties - like changing the video title - but won't work for updating relationships between entities.

For solve this problem:
attach the entity to context
load the collection(the collection is not loaded, because )
change the state of entity to modified
save changes
So your code for update should be like this:
public Video Update(Video entity)
{
//Creates database context. When it disposes, it calls context.SaveChanges()
using (var session = new DatabaseSession())
{
entity = session.Context.Set<Video>().Attach(entity);
session.Context.Entry(entity).Collection(p => p.Coworkers).Load();
session.Context.Entry(entity).State = EntityState.Modified;
}
return entity;
}

Please refer here to see how to save master detail in asp.net mvc with database first. Hopefully it will give you the idea about the code first. You may also have a look at knokout.js example

Updating a reference to a child object in Entity framework 4.1 (CodeFirst)

I'm trying to update an object that I have previously saved with EntityFramework 4.1 (CodeFirst)
The class Job has the following properties ...
public class Job
{
[key]
public int Id { get; set; }
public string Title { get; set; }
public Project Project { get; set; }
public JobType JobType { get; set; }
public string Description { get; set; }
}
The initial create works fine, but the update only commits changes to the strings..
If I change the child objects eg the JobType Property from JobTypeA to JobTypeB - the change is not committed ...
I'm not looking to commit a change to JobType - only to Job.
using (var context = new JobContext())
{
context.Jobs.Attach(job);
context.Entry(job).State = EntityState.Modified;
context.SaveChanges();
}
Having a look at SQL Profiler - the Ids are not even being sent for the Update - however they are for the initial insert!

Setting the state to Modified only updates scalar and complex properties, not your navigation properties. This only goes through Entity Framework's change detection. It means that you need to load the original from the database:
using (var context = new JobContext())
{
var originalJob = context.Jobs.Include(j => j.JobType)
.Single(j => j.Id == job.Id);
// Update scalar/complex properties
context.Entry(originalJob).CurrentValues.SetValues(job);
// Update reference
originalJob.JobType = job.JobType;
context.SaveChanges();
}
You could probably also leverage some "tricks" in your case:
using (var context = new JobContext())
{
var jobType = job.JobType;
job.JobType = null;
context.JobTypes.Attach(jobType);
context.Jobs.Attach(job);
// change detection starts from here,
// EF "thinks" now, original is JobType==null
job.JobType = jobType;
// change detection will recognize this as a change
// and send an UPDATE to the DB
context.Entry(job).State = EntityState.Modified; // for scalar/complex props
context.SaveChanges();
}
It wouldn't work though if you want to set JobType to null.
This is a typical situation which is getting much simpler if you expose foreign keys as properties in your model: With a JobTypeId in your Job entity your code would work because the FK property is scalar and setting the state to Modified will also mark this property as modified.