I ran into a problem while developing my small Blazor WASM app.
A part of my app is where users can create teams, and invite other users to join their team. The relevant Entity Classes is:
Team.cs
public class Team
{
[Key]
public Guid TeamID { get; set; }
public string Name { get; set; }
public string Abbreviation { get; set; }
public Guid? BadgeID { get; set; }
public Guid TownID { get; set; }
public Guid StatisticsID { get; set; }
public Guid CaptainID { get; set; }
public List<AppUserDTO> Players { get; set; } = new();
}
When a User accepts an invitation he should be added to the List<AppUserDTO> Players List, I do this this way on the client side:
private async Task AcceptInvite()
{
Team.Players.Add(Player);
await TeamDataService.UpdateTeam(Team);
}
public async Task UpdateTeam(Team team)
{
var teamJson =
new StringContent(JsonSerializer.Serialize(team), Encoding.UTF8, "application/json");
await _httpClient.PutAsync("api/team", teamJson);
}
But I get the following exception on the server side when I'd like to save the changes to the server:
System.InvalidOperationException: The instance of entity type 'AppUserDTO' cannot be tracked because another instance with the same key value for {'ID'} is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.
With the server-side code being:
public Team UpdateTeam(Team team)
{
var updatedTeam = _appDbContext.Teams.Include(t => t.Players).FirstOrDefault(t => t.TeamID == team.TeamID);
if (updatedTeam == null) return null;
updatedTeam.TeamID = team.TeamID;
updatedTeam.Name = team.Name;
updatedTeam.Abbreviation = team.Abbreviation;
updatedTeam.TownID = team.TownID;
updatedTeam.StatisticsID = team.StatisticsID;
updatedTeam.Players = team.Players;
updatedTeam.CaptainID = team.CaptainID;
_appDbContext.SaveChanges();
return updatedTeam;
}
The exception pops up at the _appDbContext.SaveChanges() method.
What I noticed is the following: When I add an Entity to an empty list and save it, I get no exception, but if the list already has Entities I get this error.
What would be the solution for this, I believe is quite common what I try to do, but I didn't find a solution anywhere for this.
When you execute:
var updatedTeam = _appDbContext.Teams
..Include(t => t.Players).FirstOrDefault(t => t.TeamID == team.TeamID);
... you are retrieving existing Players from the Db and _appDbContext is tracking them (by "ID").
Now, when you set Players:
updatedTeam.Players = team.Players;
... I suspect that team.Players includes Players that are already being tracked by the _appDbContext. Hence your error.
You could try:
List<Player> playersToAdd = team.Players.Except(updatedTeam.Players);
updatedTeam.AddRange(playersToAdd);
In this way, you are not adding duplicate players to the context that are already being tracked from the initial database retrieval.
Related
In my EF Core solution I have the following model:
public class Deal
{
public string Id { get; set; }
public ResponsiblePerson ResponsiblePerson1 { get; set; }
public ResponsiblePerson ResponsiblePerson2 { get; set; }
public ResponsiblePerson ResponsiblePerson3 { get; set; }
}
public class ResponsiblePerson
{
public string Id { get; set; }
public string Name { get; set; }
}
When I am trying to update Deal navigations properties:
private void UpdateResponsiblePersons(string dealId, string person1Id, string person2Id, string person3Id)
{
var existingdeal = _dbContext.Deals
.Include(d => d.ResponsiblePerson1)
.Include(d => d.ResponsiblePerson2)
.Include(d => d.ResponsiblePerson3)
.Single(d => d.Id == dealId);
existingDeal.ResponsiblePerson1 = new ResponsiblePerson { Id = person1Id };
existingDeal.ResponsiblePerson2 = new ResponsiblePerson { Id = person2Id };
existingDeal.ResponsiblePerson3 = new ResponsiblePerson { Id = person3Id };
_dbContext.Entry(deal.ResponsiblePerson1).State = EntityState.Unchanged;
_dbContext.Entry(deal.ResponsiblePerson3).State = EntityState.Unchanged;
_dbContext.Entry(deal.ResponsiblePerson3).State = EntityState.Unchanged;
_dbContext.SaveChanges();
}
EF often fails with
System.InvalidOperationException: The instance of entity type 'ResponsiblePerson' cannot be tracked because another instance with the key value '{Id: 1}' is already being tracked. When attaching existing entities, ensure that only one entity instance with a given key value is attached.
That is because sometimes existingdeal already contains the link to ResponsiblePerson with one of provided IDs in either ResponsiblePerson1 of ResponsiblePerson2 or ResponsiblePerson3 Navigation properties.
I know that one of possible solutions will be first to get ResponsiblePersons used for update from dbContext like
existingDeal.ResponsiblePerson1 = _dbContext.ResponsiblePersons.Find(person1Id)
But that means extra DB roundtrips.
Another solution is to expose foreign keys instead of navigation properties but it would make Deal model quite ugly.
Please advice me what is the best way of updating such references?
What I would like to do is duplicate/copy my School object and all of its children/associations in EF Core
I have something like the following:
var item = await _db.School
.AsNoTracking()
.Include(x => x.Students)
.Include(x => x.Teachers)
.Include(x => x.StudentClasses)
.ThenInclude(x => x.Class)
.FirstOrDefaultAsync(x => x.Id == schoolId);
I have been reading up on deep cloning and it seems that I should be able to do just add the entity...so pretty much the next line.
await _db.AddAsync(item);
Then EF should be smart enough to add that entity as a NEW entity. However, right off the bat I get a conflict that says "the id {schoolId} already exists" and will not insert. Even if I reset the Id of the new item I am trying to add, I still get conflicts with the Ids of the associations/children of the school iteam.
Is anyone familiar with this and what I might be doing wrong?
I had the same problem too, but in my case EF core was throwing exception "the id already exists".
Following the answer of #Irikos so I have created method which clones my objects.
Here's example
public class Parent
{
public int Id { get; set; }
public string SomeProperty { get; set; }
public virtual List<Child> Templates { get; set; }
public Parent Clone()
{
var output = new Parent() { SomeProperty = SomeProperty };
CloneTemplates(output);
return output;
}
private void CloneTemplates(Parent parentTo, Child oldTemplate = null, Child newTemplate = null)
{
//find old related Child elements
var templates = Templates.Where(c => c.Template == oldTemplate);
foreach (var template in templates)
{
var newEntity = new Child()
{
SomeChildProperty = template.SomeChildProperty,
Template = newTemplate,
Parent = parentTo
};
//find recursivly all related Child elements
CloneTemplates(parentTo, template, newEntity);
parentTo.Templates.Add(newEntity);
}
}
}
public class Child
{
public int Id { get; set; }
public int ParentId { get; set; }
public virtual Parent Parent { get; set; }
public int? TemplateId { get; set; }
public virtual Child Template { get; set; }
public string SomeChildProperty { get; set; }
}
Then I just call DbContext.Parents.Add(newEntity) and DbContext.SaveChanges()
That worked for me. Maybe this will be useful for someone.
I had the same problem, but in my case, ef core was smart enough save them as new entities even with existing id. However, before realising that, I just made a copy constructor for all the items, created a local task variable containing only the desired properties and returned the copy.
Remove certain properties from object upon query EF Core 2.1
I have a fairly simple data model consisting of two entities:
public class User
{
public int Id { get; set; }
public string Name { get; set; }
public int CurrentLocationId { get; set; }
public List<Location> Locations { get; set; }
public Location CurrentLocation { get; set; }
}
and
public class Location
{
public int Id { get; set; }
[Required]
public int UserId { get; set; }
public string Address { get; set; }
public User User { get; set; }
}
then in order to get a successful migration to run I needed the following model builder code:
builder.Entity<Location>()
.HasOne(x => x.User)
.WithMany(x => x.Locations)
.HasForeignKey(x => x.UserId);
This has generated a database as I'd expect and how I need it to be. However, I'm unable to save entities due to the following circular dependency error:
InvalidOperationException: Unable to save changes because a circular dependency was detected in the data to be saved: 'ForeignKey: User {'CurrentLocationId'} -> Location {'Id'} ToPrincipal: CurrentLocation, ForeignKey: Location {'UserId'} -> User {'Id'} ToDependent: Locations ToPrincipal: User'.
Is there a way around this in EF Core 2.0?
I have a few options to circumnavigate it by changing my data model, but this is the preferred approach as I can use DB constraints to ensure that all Locations link back to a User, and that every user must have a CurrentLocation set. I know it would solve the issue but I can't really allow nulls on the CurrentLocation field!
The code I'm using to try and store users is as follows (simplified for demo purposes):
var location = new Location
{
Address = "Some address"
};
_context.Locations.Add(location);
var user = new User
{
Name = "Stu"
};
_context.Users.Add(user);
user.Locations = new List<Location>
{
location
};
user.CurrentLocation = location;
await _context.SaveChangesAsync();
and I've also tried
var location = new Location
{
Address = "Some address"
};
var user = new User
{
Name = "Stu",
Locations = new List<Location>
{
location
},
CurrentLocation = location
};
_context.Users.Add(user);
await _context.SaveChangesAsync();
But the error remains the same. Can this be fixed by some kind of fancy ModelBuilder overrides? Or am I restricted to changing my data model / allowing nulls where I shouldn't really be allowing nulls?
Thanks in advance!
To answer my own question - just checked and SQL server doesn't support deferrable constraints, so nothing EF can do anyway! Change to the data model it is.
I'm trying to fetch (in disconnected way) an entity with its all related entities and then trying to update the entity. But I'm getting the following error:
Attaching an entity of type 'Feature' failed because another entity of the same type already has the same primary key value.
public class Person
{
public int PersonId { get; set; }
public string Personname { get; set }
public ICollection Addresses { get; set; }
}
public class Address
{
public int AddressId { get; set; }
public int PersonId { get; set; }
public string Line1 { get; set; }
public string City { get; set; }
public string State { get; set; }
public Person Person { get; set; }
public ICollection<Feature> Features { get; set; }
}
// Many to Many: Represented in database as AddressFeature (e.g Air Conditioning, Central Heating; User could select multiple features of a single address)
public class Feature
{
public int FeatureId { get; set; }
public string Featurename { get; set; }
public ICollection<Address> Addresses { get; set; } // Many-To-Many with Addresses
}
public Person GetCandidate(int id)
{
using (MyDbContext dbContext = new MyDbContext())
{
var person = dbContext.People.AsNoTracking().Where(x => x.PersonId == id);
person = person.Include(prop => prop.Addresses.Select(x => x.Country)).Include(prop => prop.Addresses.Select(x => x.Features));
return person.FirstOrDefault();
}
}
public void UpdateCandidate(Person newPerson)
{
Person existingPerson = GetPerson(person.Id); // Loading the existing candidate from database with ASNOTRACKING
dbContext.People.Attach(existingPerson); // This line is giving error
.....
.....
.....
}
Error:
Additional information: Attaching an entity of type 'Feature' failed because another entity of the same type already has the same primary key value.
It seems like (I may be wrong) GetCandidate is assigning every Feature within Person.Addresses a new instance. So, how could I modify the GetCandidate to make sure that the same instance (for same values) is bing assisgned to Person.Addresses --> Features.
Kindly suggest.
It seems like (I may be wrong) GetCandidate is assigning every Feature within Person.Addresses a new instance. So, how could I modify the GetCandidate to make sure that the same instance (for same values) is bing assisgned to Person.Addresses --> Features.
Since you are using a short lived DbContext for retrieving the data, all you need is to remove AsNoTracking(), thus allowing EF to use the context cache and consolidate the Feature entities. EF tracking serves different purposes. One is to allow consolidating the entity instances with the same PK which you are interested in this case, and the second is to detect the modifications in case you modify the entities and call SaveChanges(), which apparently you are not interested when using the context simply to retrieve the data. When you disable the tracking for a query, EF cannot use the cache, thus generates separate object instances.
What you really not want is to let EF create proxies which hold reference to the context used to obtain them and will cause issues when trying to attach to another context. I don't see virtual navigation properties in your models, so most likely EF will not create proxies, but in order to be absolutely sure, I would turn ProxyCreationEnabled off:
public Person GetCandidate(int id)
{
using (MyDbContext dbContext = new MyDbContext())
{
dbContext.Configuration.ProxyCreationEnabled = false;
var person = dbContext.People.Where(x => x.PersonId == id);
person = person.Include(prop => prop.Addresses.Select(x => x.Country)).Include(prop => prop.Addresses.Select(x => x.Features));
return person.FirstOrDefault();
}
}
I have a trouble with EF (6.1.3)
I have created next classes (with many-to-many relationship):
public class Record
{
[Key]
public int RecordId { get; set; }
[Required]
public string Text { get; set; }
public virtual ICollection<Tag> Tags { get; set; }
}
public class Tag
{
[Key]
public int TagId { get; set; }
[Required]
public string Name { get; set; }
public virtual ICollection<Record> Records{ get; set; }
}
And method:
void AddTags()
{
Record[] records;
Tag[] tags;
using (var context = new AppDbContext())
{
records = context.Records.ToArray();
}//remove line to fix
tags = Enumerable.Range(0, 5).Select(x => new Tag()
{
Name = string.Format("Tag_{0}", x),
Records= records.Skip(x * 5).Take(5).ToArray()
}).ToArray();
using (var context = new AppDbContext()){ //remove line to fix
context.Tags.AddRange(tags);
context.SaveChanges();
}
}
If I use two contexts, the records (which were added to created tags) will be duplicated. If I remove marked rows - problem disappears.
Is there any way to fix this problem without using the same context?
If you can, better reload entities or not detach them at all. Using multiple context instances in application is overall making things much more complicated.
The problem for you comes from the Entity Framework entity change tracker. When you load entitites from your DbContext and dispose that context, entities get detached from entity change tracker, and Entity Framework has no knowledge of any changes made to it.
After you reference detached entity by an attached entity, it (detached entity) immediately gets into entity change tracker, and it has no idea that this entity was loaded before. To give Entity Framework an idea that this detached entity comes from the database, you have to reattach it:
foreach (var record in records) {
dbContext.Entry(record).State = EntityState.Unchanged;
}
This way you will be able to use records to reference in other objects, but if you have any changes made to these records, then all these changes will go away. To make changes apply to database you have to change state to Added:
dbContext.Entry(record).State = EntityState.Modified;
Entity Framework uses your mappings to determine row in database to apply changes to, specifically using your Primary Key settings.
A couple examples:
public class Bird
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
public string Color { get; set; }
}
public class Tree
{
[Key]
public int Id { get; set; }
public string Name { get; set; }
}
public class BirdOnATree
{
[Column(Order = 0), Key, ForeignKey("Bird")]
public int BirdId { get; set; }
public Bird Bird { get; set; }
[Column(Order = 1), Key, ForeignKey("Tree")]
public int TreeId { get; set; }
public Tree Tree { get; set; }
public DateTime SittingSessionStartedAt { get; set; }
}
Here's a small entity structure so that you could see how it works. You can see that Bird and Tree have simple Key - Id. BirdOnATree is a many-to-many table for Bird-Tree pair with additional column SittingSessionStartedAt.
Here's the code for multiple contexts:
Bird bird;
using (var context = new TestDbContext())
{
bird = context.Birds.First();
}
using (var context = new TestDbContext())
{
var tree = context.Trees.First();
var newBirdOnAtree = context.BirdsOnTrees.Create();
newBirdOnAtree.Bird = bird;
newBirdOnAtree.Tree = tree;
newBirdOnAtree.SittingSessionStartedAt = DateTime.UtcNow;
context.BirdsOnTrees.Add(newBirdOnAtree);
context.SaveChanges();
}
In this case, bird was detached from the DB and not attached again. Entity Framework will account this entity as a new entity, which never existed in DB, even though Id property is set to point to existing row to database. To change this you just add this line to second DbContext right in the beginning:
context.Entry(bird).State = EntityState.Unchanged;
If this code is executed, it will not create new Bird entity in DB, but use existing instead.
Second example: instead of getting bird from the database, we create it by ourselves:
bird = new Bird
{
Id = 1,
Name = "Nightingale",
Color = "Gray"
}; // these data are different in DB
When executed, this code will also not create another bird entity, will make a reference to bird with Id = 1 in BirdOnATree table, and will not update bird entity with Id = 1. In fact you can put any data here, just use correct Id.
If we change our code here to make this detached entity update existing row in DB:
context.Entry(bird).State = EntityState.Modified;
This way, correct data will be inserted to table BirdOnATree, but also row with Id = 1 will be updated in table Bird to fit the data you provided in the application.
You can check this article about object state tracking:
https://msdn.microsoft.com/en-US/library/dd456848(v=vs.100).aspx
Overall, if you can avoid this, don't use object state tracking and related code. It might come to unwanted changes that are hard to find source for - fields are updated for entity when you don't expect them to, or are not updated when you expect it.