I am trying to insert a room into my database from a textbox input (int), a combobox that shows all the buildings from the database and a combobox that shows all the floors from the database, I am encountering this error:
"An entity object cannot be referenced by multiple instances of IEntityChangeTracker."
and not quite sure how to solve this.
FormAddRoom.cs:
http://pastebin.com/Cst5bBbD
Data Models:
public class Building
{
public int BuildingID { get; set; }
public string Name { get; set; }
public Hotel Hotel { get; set; }
public virtual ICollection<Floor> Floors { get; set; }
}
public class Floor
{
public int FloorID { get; set; }
public string Name { get; set; }
public virtual Building Building { get; set; }
public virtual ICollection<Room> Rooms { get; set; }
}
public class RoomType
{
public int RoomTypeID { get; set; }
public string Name { get; set; }
}
Databasehandler methods:
public static List<Building> GetAllBuildingsByHotel(string hotel)
{
HotelDbContext context = new HotelDbContext();
var buildings = context.Buildings.Where(b => b.Hotel.Name == hotel).ToList();
return buildings;
}
public static List<Floor> GetAllFloorsFromBuilding(int buildingid)
{
HotelDbContext context = new HotelDbContext();
var floors = context.Floors.Where(f => f.Building.BuildingID == buildingid).ToList();
return floors;
}
public static int InsertRoom(Room room)
{
HotelDbContext context = new HotelDbContext();
context.Rooms.Add(room);
context.SaveChanges();
return room.RoomID;
}
If you're using tracked entities (the default EF settings), you can't get an object from one instance of a context and put it in another. You need to do all your work against a single context instance.
Related
HI I have two Tables( Movie as Movy Entity and Producers as Producer). Movie has one producer and producer has many movies.here is the er diag
Picture: ER Diagram
When i set the data soure of my DataGridView to ctx.Movies.ToList() some movie in the list doesnt have any producer. even though its not null in database.
Picture:Program with missing producer
//Movie Entity Class
public partial class Movy
{
public short VideoCode { get; set; }
public string MovieTitle { get; set; }
public string MovieType { get; set; }
public string Rating { get; set; }
public Nullable<float> RentalPrice { get; set; }
public string ProducerID { get; set; }
public string Director { get; set; }
public string Media { get; set; }
public Nullable<short> TotalStock { get; set; }
public Nullable<short> NumberRented { get; set; }
public virtual Producer Producer { get; set; }
}
}
//Producer Entity Class
public partial class Producer
{
public Producer()
{
this.Movies = new HashSet<Movy>();
}
public string ProducerID { get; set; }
public string ProducerName { get; set; }
public string CountryCode { get; set; }
public virtual ICollection<Movy> Movies { get; set; }
}
// MyDBEntities ctx
public partial class MYDBEntities : DbContext
{
public MYDBEntities()
: base("name=MYDBEntities")
{
}
public virtual DbSet<Movy> Movies { get; set; }
public virtual DbSet<Producer> Producers { get; set; }
}
//this is my function in windows form which is having some producer missing in movie datalist. i have added the picture of output
private void Form1_Load(object sender, EventArgs e)
{
MYDBEntities ct = new MYDBEntities();
dataGridView1.DataSource = ct.Movies.ToList();
}
P.S: [Picture:Database data]
/* i checked each product and its producer. some producer is null there.
even though its not null in database(I have uploaded db pic) [3]*/
List<Movy> ls = ct.Movies.ToList();
foreach(Movy mov in ls)
{
//some mov.Producer is null here.
}
You can try with Include method.
MYDBEntities ct = new MYDBEntities();
dataGridView1.DataSource = ct.Movies.Include("Producer").ToList();
Alright I found the problem. it is Entity Framework wasn't able to automap some string foreign key.
for me those movie was having producerID = 'Universal' foreign key, that movies Producer Object was null(Couldn't map). so once I update my database like using following query follwoing: it working now:
update Movies set Producer='Warner' where Producer='Universal';
I have created classes using EF Code First that have collections of each other.
Entities:
public class Field
{
public int Id { get; set; }
public string Name { get; set; }
public virtual List<AppUser> Teachers { get; set; }
public Field()
{
Teachers = new List<AppUser>();
}
}
public class AppUser
{
public int Id { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public string UserName => Email;
public virtual List<Field> Fields { get; set; }
public AppUser()
{
Fields = new List<FieldDTO>();
}
}
DTOs:
public class FieldDTO
{
public int Id { get; set; }
public string Name { get; set; }
public List<AppUserDTO> Teachers { get; set; }
public FieldDTO()
{
Teachers = new List<AppUserDTO>();
}
}
public class AppUserDTO
{
public int Id { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public string UserName => Email;
public List<FieldDTO> Fields { get; set; }
public AppUserDTO()
{
Fields = new List<FieldDTO>();
}
}
Mappings:
Mapper.CreateMap<Field, FieldDTO>();
Mapper.CreateMap<FieldDTO, Field>();
Mapper.CreateMap<AppUserDTO, AppUser>();
Mapper.CreateMap<AppUser, AppUserDTO>();
And I am getting StackOverflowException when calling this code (Context is my dbContext):
protected override IQueryable<FieldDTO> GetQueryable()
{
IQueryable<Field> query = Context.Fields;
return query.ProjectTo<FieldDTO>();//exception thrown here
}
I guess this happens because it loops in Lists calling each other endlessly. But I do not understand why this happens. Are my mappings wrong?
You have self-referencing entities AND self-referencing DTOs. Generally speaking self-referencing DTOs are a bad idea. Especially when doing a projection - EF does not know how to join together and join together and join together a hierarchy of items.
You have two choices.
First, you can force a specific depth of hierarchy by explicitly modeling your DTOs with a hierarchy in mind:
public class FieldDTO
{
public int Id { get; set; }
public string Name { get; set; }
public List<TeacherDTO> Teachers { get; set; }
public FieldDTO()
{
Teachers = new List<TeacherDTO>();
}
}
public class TeacherDTO
{
public int Id { get; set; }
public string Email { get; set; }
public string Password { get; set; }
public string UserName => Email;
}
public class AppUserDTO : TeacherDTO
{
public List<FieldDTO> Fields { get; set; }
public AppUserDTO()
{
Fields = new List<FieldDTO>();
}
}
This is the preferred way, as it's the most obvious and explicit.
The less obvious, less explicit way is to configure AutoMapper to have a maximum depth it will go to traverse hierarchical relationships:
CreateMap<AppUser, AppUserDTO>().MaxDepth(3);
I prefer to go #1 because it's the most easily understood, but #2 works as well.
Other option is using PreserveReferences() method.
CreateMap<AppUser, AppUserDTO>().PreserveReferences();
I use this generic method:
public static TTarget Convert<TSource, TTarget>(TSource sourceItem)
{
if (null == sourceItem)
{
return default(TTarget);
}
var deserializeSettings = new JsonSerializerSettings { ObjectCreationHandling = ObjectCreationHandling.Replace, ReferenceLoopHandling = ReferenceLoopHandling.Ignore };
var serializedObject = JsonConvert.SerializeObject(sourceItem, deserializeSettings);
return JsonConvert.DeserializeObject<TTarget>(serializedObject);
}
...
MapperConfiguration(cfg =>
{
cfg.ForAllMaps((map, exp) => exp.MaxDepth(1));
...
When you giving 1 navigation_property to 2nd entity and visa-versa it go in an infinite loop state. So, the compiler automatically throws a Stackoverflow exception.
So, to avoid that, you just need to remove one navigation_property from any of the entities.
I have the following scenario. We need to be able to fill forms for some tables, examples Companies (Empresa in Spanish), however we want the administrator to be able to extend the entity itself with additional fields.
I designed the following classes, and I need to seed at least one row, however its unclear to me how to seed one row of type CampoAdicional
Entity class:
public abstract class Entidad
{
[Key]
public int Id { get; set; }
}
Company Class (Empresas)
public class Empresa : Entidad
{
public string Nombre { get; set; }
public string NIT { get; set; }
public string NombreRepresentanteLegal { get; set; }
public string TelefonoRepresentanteLegal { get; set; }
public string NombreContacto { get; set; }
public string TelefonoContacto { get; set; }
public virtual ICollection<CampoAdicional> CamposAdicionales { get; set; }
}
And the Additional Fields (Campo Adicional)
public class CampoAdicional
{
[Key]
public int Id { get; set; }
public string NombreCampo { get; set; }
public virtual Tiposcampo TipoCampo { get; set; }
public virtual Entidad Entidad { get; set; }
}
However I dont know how to seed this class or table, because entity should be of subtype Company
Obviously the typeof doesnt compile
context.CampoAdicionals.Add(new CampoAdicional() { Entidad = typeof(Empresa), Id = 1, NombreCampo = "TwitterHandle", TipoCampo = Tiposcampo.TextoUnaLinea });
Update 1: Please note that the additional fields are for the entire entity company not for each company.
Unfortunately, I don't think you'll be able to use EF to automatically create that kind of relationship. You might be able to do something similar with special getters and such:
public class Entidad
{
// stuff...
public IEnumerable<CampoAdicional> CamposAdicionales
{
get { return CampoAdicional.GetAll(this); }
}
}
public class CampoAdicional
{
[Key]
public int Id { get; set; }
public string NombreCampo { get; set; }
public virtual Tiposcampo TipoCampo { get; set; }
protected string EntidadType { get; set; }
// You will need some mapping between Type and the EntidadType string
// that will be stored in the database.
// Maybe Type.FullName and Type.GetType(string)?
protected Type MapEntidadTypeToType();
protected string MapTypeToEntidadType(Type t);
[NotMapped]
public Type
{
get { return MapEntidadTypeToType(); }
// maybe also check that Entidad.IsAssignableFrom(value) == true
set { EntidadType = MapTypeToEntidadType(value); }
}
public static IEnumerable<CampoAdicional> GetAll(Entidad ent)
{
return context.CampoAdicionals
.Where(a => a.EntidadType == MapTypeToEntidadType(ent.GetType()));
}
}
I have two API calls. GetExam and SaveExam. GetExam serializes to JSON which means by the time I go to save, the entity is detached. This isnt a problem, I can go retrieve the entity by its primary key and update its properties manually.
However, when I do so the exam questions get its current collection duplicated. For example, if examToSave.ExamQuestions had a few questions deleted, and a new one added all selectedExam.exam_question are duplicated and the new one is added in. Eg. if 3 questions existed, I deleted 1 and added 4 there will now be 7.
Domain models:
public partial class exam
{
public exam()
{
this.exam_question = new HashSet<exam_question>();
}
public int ID { get; set; }
public string ExamName { get; set; }
public string ExamDesc { get; set; }
public Nullable<decimal> TimeToComplete { get; set; }
public bool AllowBackStep { get; set; }
public bool RandomizeAnswerOrder { get; set; }
public int Attempts { get; set; }
public virtual ICollection<exam_question> exam_question { get; set; }
}
public partial class exam_question
{
public exam_question()
{
this.exam_answer = new HashSet<exam_answer>();
}
public int ID { get; set; }
public int ExamID { get; set; }
public string QuestionText { get; set; }
public bool IsFreeForm { get; set; }
public virtual exam exam { get; set; }
public virtual ICollection<exam_answer> exam_answer { get; set; }
}
public partial class exam_answer
{
public int ID { get; set; }
public string AnswerText { get; set; }
public int QuestionID { get; set; }
public bool IsCorrect { get; set; }
public virtual exam_question exam_question { get; set; }
}
Save method:
[Route("SaveExam")]
[HttpPost]
public IHttpActionResult SaveExam(ExamViewModel examToSave)
{
using (var db = new IntranetEntities())
{
// try to locate the desired exam to update
var selectedExam = db.exams.Where(w => w.ID == examToSave.ID).SingleOrDefault();
if (selectedExam == null)
{
return NotFound();
}
// Redacted business logic
// Map the viewmodel to the domain model
Mapper.CreateMap<ExamAnswerViewModel, exam_answer>();
Mapper.CreateMap<ExamQuestionViewModel, exam_question>().ForMember(dest => dest.exam_answer, opt => opt.MapFrom(src => src.QuestionAnswers));
Mapper.CreateMap<ExamViewModel, exam>().ForMember(dest => dest.exam_question, opt => opt.MapFrom(src => src.ExamQuestions));
var viewmodel = Mapper.Map<exam>(examToSave);
// Update exam properties
selectedExam.ExamName = viewmodel.ExamName;
selectedExam.ExamDesc = viewmodel.ExamDesc;
selectedExam.AllowBackStep = viewmodel.AllowBackStep;
selectedExam.Attempts = viewmodel.Attempts;
selectedExam.RandomizeAnswerOrder = viewmodel.RandomizeAnswerOrder;
selectedExam.exam_question = viewmodel.exam_question; // DUPLICATES PROPS
// Save
db.SaveChanges();
return Ok(examToSave);
}
}
I have a Model like this
public class Challenge
{
public int ID { get; set; }
public string Name { get; set; }
public string Blurb { get; set; }
public int Points { get; set; }
public string Category { get; set; }
public string Flag { get; set; }
public List<string> SolvedBy { get; set; }
}
public class ChallengeDBContext : DbContext
{
public DbSet<Challenge> Challenges { get; set; }
}
and then Controller like this. But I cannot update the List "SolvedBy", the next time I step through with the debugger, the list is still empty.
[HttpPost]
public string Index(string flag = "", int id=0)
{
Challenge challenge = db.Challenges.Find(id);
if (flag == challenge.Flag)
{
var chall = db.Challenges.Find(id);
if (chall.SolvedBy == null)
{
chall.SolvedBy = new List<string>();
}
chall.SolvedBy.Add(User.Identity.Name);
db.Entry(chall).State = EntityState.Modified;
db.SaveChanges();
//congrats, you solved the puzzle
return "got it";
}
else
{
return "fail";
}
}
is there any way around it to make a list of strings kept in the database?
EF don't know how to store an array in database table so it just ignore it. You can create another table/entity or use XML/JSON to store the list. You can serialize the list before saving and deserialize it after loading from database
A List<T> in a model would normally map to a second table, but in your DbContext you only have a single table. Try adding a second table.
public class ChallengeDBContext : DbContext
{
public DbSet<Challenge> Challenges { get; set; }
public DbSet<Solution> Solutions {get; set;}
}
public class Challenge
{
public int ID { get; set; }
public string Name { get; set; }
public string Blurb { get; set; }
public int Points { get; set; }
public string Category { get; set; }
public string Flag { get; set; }
public List<Solution> SolvedBy { get; set; }
}
public class Solution
{
public int ID { get; set; }
public string Name { get; set; }
}
Then your controller can use code along the lines of...
var chall = db.Challenges.Find(id);
if (chall.SolvedBy == null)
{
chall.SolvedBy = new List<Solution>();
}
chall.SolvedBy.Add(new Solution {Name=User.Identity.Name});
None of the above has been tested and I may have made some mistakes there, but the general principle I want to illustrate is the fact that you need another table. The List<T> represents a JOIN in SQL.