Develop Reference

Why is Entity Framework Core attempting to insert records into one of the tables from many to many relationships and NOT the join table?

Given the following set up where there are many Teams and there are many LeagueSessions. Each Team belongs to zero or more LeagueSessions but only ever one LeagueSession is active. LeagueSessions have many teams, and the teams will be repeated. Many-to-many relationship is established between Teams and LeagueSessions with a join table called TeamsSessions.
Team model looks like this:
public class Team
{
public string Id { get; set; }
public string Name { get; set; }
public League League { get; set; }
public string LeagueID { get; set; }
public bool Selected { get; set; }
public ICollection<Match> Matches { get; set; }
public virtual ICollection<TeamSession> TeamsSessions { get; set; }
}
Team model fluent api configuration:
`
public class TeamConfiguration
{
public TeamConfiguration(EntityTypeBuilder<Team> model)
{
// The data for this model will be generated inside ThePLeagueDataCore.DataBaseInitializer.DatabaseBaseInitializer.cs class
// When generating data for models in here, you have to provide it with an ID, and it became mildly problematic to consistently get
// a unique ID for all the teams. In ThePLeagueDataCore.DataBaseInitializer.DatabaseBaseInitializer.cs we can use dbContext to generate
// unique ids for us for each team.
model.HasOne(team => team.League)
.WithMany(league => league.Teams)
.HasForeignKey(team => team.LeagueID);
}
}
`
Each team belongs to a single League. League model looks like this:
`public class League
{
public string Id { get; set; }
public string Type { get; set; }
public string Name { get; set; }
public IEnumerable<Team> Teams { get; set; }
public bool Selected { get; set; }
public string SportTypeID { get; set; }
public SportType SportType { get; set; }
public IEnumerable<LeagueSessionSchedule> Sessions { get; set; }
}`
fluent API for the League:
`public LeagueConfiguration(EntityTypeBuilder<League> model)
{
model.HasOne(league => league.SportType)
.WithMany(sportType => sportType.Leagues)
.HasForeignKey(league => league.SportTypeID);
model.HasMany(league => league.Teams)
.WithOne(team => team.League)
.HasForeignKey(team => team.LeagueID);
model.HasData(leagues);
}`
SessionScheduleBase class looks like this:
public class SessionScheduleBase
{
public string LeagueID { get; set; }
public bool ByeWeeks { get; set; }
public long? NumberOfWeeks { get; set; }
public DateTime SessionStart { get; set; }
public DateTime SessionEnd { get; set; }
public ICollection<TeamSession> TeamsSessions { get; set; } = new Collection<TeamSession>();
public ICollection<GameDay> GamesDays { get; set; } = new Collection<GameDay>();
}
Note: LeagueSessionSchedule inherits from SessionScheduleBase
The TeamSession model looks like this:
`public class TeamSession
{
public string Id { get; set; }
public string TeamId { get; set; }
public Team Team { get; set; }
public string LeagueSessionScheduleId { get; set; }
public LeagueSessionSchedule LeagueSessionSchedule { get; set; }
}`
I then configure the relationship with the fluent API like this:
`public TeamSessionConfiguration(EntityTypeBuilder<TeamSession> model)
{
model.HasKey(ts => new { ts.TeamId, ts.LeagueSessionScheduleId });
model.HasOne(ts => ts.Team)
.WithMany(t => t.TeamsSessions)
.HasForeignKey(ts => ts.TeamId);
model.HasOne(ts => ts.LeagueSessionSchedule)
.WithMany(s => s.TeamsSessions)
.HasForeignKey(ts => ts.LeagueSessionScheduleId);
}`
The problem arises whenever I attempt to insert a new LeagueSessionSchedule. The way I am adding a new TeamSession object onto the new LeagueSessionSchedule is like this:
`foreach (TeamSessionViewModel teamSession in newSchedule.TeamsSessions)
{
Team team = await this._teamRepository.GetByIdAsync(teamSession.TeamId, ct);
if(team != null)
{
TeamSession newTeamSession = new TeamSession()
{
Team = team,
LeagueSessionSchedule = leagueSessionSchedule
};
leagueSessionSchedule.TeamsSessions.Add(newTeamSession);
}
}`
Saving the new LeagueSessionSchedule code:
public async Task<LeagueSessionSchedule> AddScheduleAsync(LeagueSessionSchedule newLeagueSessionSchedule, CancellationToken ct = default)
{
this._dbContext.LeagueSessions.Add(newLeagueSessionSchedule);
await this._dbContext.SaveChangesAsync(ct);
return newLeagueSessionSchedule;
}
Saving the new LeagueSessionSchedule object throws an error by Entity Framework Core that it cannot INSERT a duplicate primary key value into the dbo.Teams table. I have no idea why its attempting to add to dbo.Teams table and not into TeamsSessions table.
ERROR:
INSERT INTO [LeagueSessions] ([Id], [Active], [ByeWeeks], [LeagueID], [NumberOfWeeks], [SessionEnd], [SessionStart])
VALUES (#p0, #p1, #p2, #p3, #p4, #p5, #p6);
INSERT INTO [Teams] ([Id], [Discriminator], [LeagueID], [Name], [Selected])
VALUES (#p7, #p8, #p9, #p10, #p11),
(#p12, #p13, #p14, #p15, #p16),
(#p17, #p18, #p19, #p20, #p21),
(#p22, #p23, #p24, #p25, #p26),
(#p27, #p28, #p29, #p30, #p31),
(#p32, #p33, #p34, #p35, #p36),
(#p37, #p38, #p39, #p40, #p41),
(#p42, #p43, #p44, #p45, #p46);
System.Data.SqlClient.SqlException (0x80131904): Violation of PRIMARY KEY constraint 'PK_Teams'. Cannot insert duplicate key in object 'dbo.Teams'. The duplicate key value is (217e2e11-0603-4239-aab5-9e2f1d3ebc2c).
My goal is to create a new LeagueSessionSchedule object. Along with the creation of this object, I also have to create a new TeamSession entry to the join table (or not if join table is not necessary) to then be able to pick any given team and see what session it is currently a part of.
My entire PublishSchedule method is the following:
`
public async Task<bool> PublishSessionsSchedulesAsync(List<LeagueSessionScheduleViewModel> newLeagueSessionsSchedules, CancellationToken ct = default(CancellationToken))
{
List<LeagueSessionSchedule> leagueSessionOperations = new List<LeagueSessionSchedule>();
foreach (LeagueSessionScheduleViewModel newSchedule in newLeagueSessionsSchedules)
{
LeagueSessionSchedule leagueSessionSchedule = new LeagueSessionSchedule()
{
Active = newSchedule.Active,
LeagueID = newSchedule.LeagueID,
ByeWeeks = newSchedule.ByeWeeks,
NumberOfWeeks = newSchedule.NumberOfWeeks,
SessionStart = newSchedule.SessionStart,
SessionEnd = newSchedule.SessionEnd
};
// leagueSessionSchedule = await this._sessionScheduleRepository.AddScheduleAsync(leagueSessionSchedule, ct);
// create game day entry for all configured game days
foreach (GameDayViewModel gameDay in newSchedule.GamesDays)
{
GameDay newGameDay = new GameDay()
{
GamesDay = gameDay.GamesDay
};
// leagueSessionSchedule.GamesDays.Add(newGameDay);
// create game time entry for every game day
foreach (GameTimeViewModel gameTime in gameDay.GamesTimes)
{
GameTime newGameTime = new GameTime()
{
GamesTime = DateTimeOffset.FromUnixTimeSeconds(gameTime.GamesTime).DateTime.ToLocalTime(),
// GameDayId = newGameDay.Id
};
// newGameTime = await this._sessionScheduleRepository.AddGameTimeAsync(newGameTime, ct);
newGameDay.GamesTimes.Add(newGameTime);
}
leagueSessionSchedule.GamesDays.Add(newGameDay);
}
// update teams sessions
foreach (TeamSessionViewModel teamSession in newSchedule.TeamsSessions)
{
// retrieve the team with the corresponding id
Team team = await this._teamRepository.GetByIdAsync(teamSession.TeamId, ct);
if(team != null)
{
TeamSession newTeamSession = new TeamSession()
{
Team = team,
LeagueSessionSchedule = leagueSessionSchedule
};
leagueSessionSchedule.TeamsSessions.Add(newTeamSession);
}
}
// update matches for this session
foreach (MatchViewModel match in newSchedule.Matches)
{
Match newMatch = new Match()
{
DateTime = match.DateTime,
HomeTeamId = match.HomeTeam.Id,
AwayTeamId = match.AwayTeam.Id,
LeagueID = match.LeagueID
};
leagueSessionSchedule.Matches.Add(newMatch);
}
try
{
leagueSessionOperations.Add(await this._sessionScheduleRepository.AddScheduleAsync(leagueSessionSchedule, ct));
}
catch(Exception ex)
{
}
}
// ensure all leagueSessionOperations did not return any null values
return leagueSessionOperations.All(op => op != null);
}
`

This is not a many-to-many relationship.
It is two separate one-to-many relationships, which happen to refer to the same table on one end of the relationship.
While it is true that on the database level, both use cases are represented by three tables, i.e. Foo 1->* FooBar *<-1 Bar, these two cases are treated differently by Entity Framework's automated behavior - and this is very important.
EF only handles the cross table for you if it is a direct many-to-many, e.g.
public class Foo
{
public virtual ICollection<Bar> Bars { get; set; }
}
public class Bar
{
public virtual ICollection<Foo> Foos { get; set; }
}
EF handles the cross table behind the scenes, and you are never made aware of the existence of the cross table (from the code perspective).
Importantly, EF Core does not yet support implicit cross tables! There is currently no way to do this in EF Core, but even if there were, you're not using it anyway, so the answer to your problem remains the same regardless of whether you're using EF or EF Core.
However, you have defined your own cross table. While this is still representative of a many-to-many relationship in database terms, it has ceased to be a many-to-many relationship as far as EF is concerned, and any documentation you find on EF's many-to-many relationships no longer applies to your scenario.
Unattached but indirectly added objects are assumed to be new.
By "indirectly added", I mean you that it was added to the context as part of another entity (which you directly added to the context). In the following example, foo is directly added and bar is indirectly added:
var foo = new Foo();
var bar = new Bar();
foo.Bar = bar;
context.Foos.Add(foo); // directly adding foo
// ... but not bar
context.SaveChanges();
When you add (and commit) a new entity to the context, EF adds it for you. However, EF also looks at any related entities that the first entity contains. During the commit in the above example, EF will look at both the foo and bar entities and will handle them accordingly. EF is smart enough to realize that you want bar to be stored in the database since you put it inside the foo object and you explicitly asked EF to add foo to the database.
It is important to realize that you've told EF that foo should be created (since you called Add(), which implies a new item), but you never told EF what it should do with bar. It's unclear (to EF) what you expect EF to do with this, and thus EF is left guessing at what to do.
If you never explained to EF whether bar already exists or not, Entity Framework defaults to assuming it needs to create this entity in the database.
Saving the new LeagueSessionSchedule object throws an error by Entity Framework Core that it cannot INSERT a duplicate primary key value into the dbo.Teams table. I have no idea why its attempting to add to dbo.Teams table
Knowing what you now know, the error becomes clearer. EF is trying to add this team (which was the bar object in my example) because it has no information on this team object and what its state in the database is.
There are a few solutions here.
1. Use the FK property instead of the navigational property
This is my preferred solution because it leaves no room for error. If the team ID does not yet exist, you get an error. At no point will EF try to create a team, since it doesn't even know the team's data, it only knows the (alleged) ID you're trying to create a relationship with.
Note: I am omitting LeagueSessionSchedule as it is unrelated to the current error - but it's essentially the same behavior for both Team and LeagueSessionSchedule.
TeamSession newTeamSession = new TeamSession()
{
TeamId = team.Id
};
By using the FK property instead of the nav prop, you are informing EF that this is an existing team - and therefore EF no longer tries to (re)create this team.
2. Ensure that the team is tracked by the current context
Note: I am omitting LeagueSessionSchedule as it is unrelated to the current error - but it's essentially the same behavior for both Team and LeagueSessionSchedule.
context.Teams.Attach(team);
TeamSession newTeamSession = new TeamSession()
{
Team = team
};
By attaching the object to the context, you are informing it of its existence. The default state of a newly attached entity is Unchanged, meaning "this already exists in the database and has not been changed - so you don't need to update it when we commit the context".
If you have actually made changes to your team that you want to be updated during commit, you should instead use:
context.Entry(team).State = EntityState.Modified;
Entry() inherently also attaches the entity, and by setting its state to Modified you ensure that the new values will be committed to the database when you call SaveChanges().
Note that I prefer solution 1 over solution 2 because it's foolproof and much less likely to lead to unexpected behavior or runtime exceptions.
String primary keys are undesirable
I'm not going to say that it doesn't work, but strings cannot be autogenerated by Entity Framework, making them undesirable as the type of your entity's PK. You will need to manually set your entity PK values.
Like I said, it's not impossible, but your code shows that you're not explicitly setting PK values:
if(team != null)
{
TeamSession newTeamSession = new TeamSession()
{
Team = team,
LeagueSessionSchedule = leagueSessionSchedule
};
leagueSessionSchedule.TeamsSessions.Add(newTeamSession);
}
If you want your PK's to be automatically generated, use an appropriate type. int and Guid are by far the most commonly used types for this.
Otherwise, you're going to have to start setting your own PK values, because if you don't (and the Id value thus defaults to null), your code is going to fail when you add a second TeamSession object using the above code (even though you're doing everything else correctly), since PK null is already taken by the first entity you added to the table.

Concisely Insert/Update/Delete Enumerable Child Entities using Automapper

I am working on an ASP.Net MVC application and I have a "Report" object that has related enumerables such as schedules and comments. Using AutoMapper, it has been easy to convert from a report entity to a View Model and back, but I have issues when I try to save the Report object (mapped to an existing entity from a view model) back to the database.
More specifically, I can't seem to concisely update existing entities, insert new entities, and delete old entities using automapper. For instance whenever I map schedules from the view model to a report entity, it deletes the existing schedules and then creates new ones (with incremented indexes). This is my code:
public class ScheduleViewModel
{
public int ScheduleID { get; set; }
public int ReportID { get; set; }
public int Month { get; set; }
public int Day { get; set; }
public string Description { get; set; }
}
public class ReportViewModel
{
public int ReportID { get; set; }
public List<ScheduleViewModel> Schedules { get; set; }
public void Save()
{
dbContext db = new dbContext();
Report original = db.Reports.SingleOrDefault(o => o.ReportID == ReportID);
var config = new MapperConfiguration(cfg =>
{
cfg.CreateMap<ReportViewModel, Report>();
});
config.AssertConfigurationIsValid();
var mapper = config.CreateMapper();
mapper.Map(this, original);
db.SaveChanges();
}
}
My Report object has a relational key (and a "Schedules" navigational property), so everything is mapped successfully from my view model to the "original" Report. New schedules have a ScheduleID of 0, since they haven't been assigned, and they get added to the database using the auto-increment, which is what I want. The existing schedules maintain their ScheduleID when mapped to the "original" report object, but then recieve incremented IDs once SaveChanges is called.
As I understand it, I'm attaching new schedules to the context whether or not the view model ID properties match the primary key in the database (in this case it is a composite of ReportID and ScheduleID). Is there a clean way, using some sort of ForMember(report => report.Schedules), expression that makes Entity Framework understand to not destroy my existing entities if a View Model object can map to an existing Key?
I am looking for something that functions similar to the code below, but since I will have many enumerable properties attached to my report objects, I don't want to maintain these sections for each:
foreach (Schedule schedule in db.Schedules.Where(s => s.ReportID == this.ReportID))
{
ScheduleViewModel svm = this.Schedules.FirstOrDefault(s => s.ScheduleID == schedule.ScheduleID);
//Update Existing
if (svm != null)
db.Entry(schedule).CurrentValues.SetValues(svm);
//Delete Missing
else
db.Entry(schedule).State = System.Data.Entity.EntityState.Deleted;
}
//Insert New
foreach(ScheduleViewModel svm in this.Schedules.Where(s => s.ScheduleID == 0))
{
svm.ReportID = ReportID;
Schedule schedule = new Schedule() {};
db.Schedules.Add(schedule);
db.Entry(schedule).CurrentValues.SetValues(svm);
}

Apparently this is not currently possible with AutoMapper. Instead of mapping individual entities, AutoMapper destroys the existing entity collection and creates a new one with the same properties. I'm sure that works fine for some applications, but with Entity Framework's change tracking it is telling the database to delete the existing records and insert new ones, with new IDs. Unfortunately it seems collections have to be mapped individually/manually using the method I posted in my original question. Rather than repeating that for every collection, though, I wrote a generic handler that will map a model collection to an entity collection using a specified key -- without destroying the entities:
public void UpdateEntitySet<T>(IEnumerable<object> models, IEnumerable<T> entities, string key) where T : class
{
Dictionary<object, T> entityDictionary = new Dictionary<object, T>();
foreach(T entity in entities)
{
var entityKey = entity.GetType().GetProperty(key).GetValue(entity);
entityDictionary.Add(entityKey, entity);
}
if (models != null)
{
foreach (object model in models)
{
var modelKey = model.GetType().GetProperty(key).GetValue(model);
var existingEntity = entityDictionary.SingleOrDefault(d => Object.Equals(d.Key, modelKey)).Value;
if (existingEntity == null)
{
var newEntity = db.Set<T>().Create();
db.Set<T>().Add(newEntity);
db.Entry(newEntity).CurrentValues.SetValues(model);
}
else
{
db.Entry(existingEntity).CurrentValues.SetValues(model);
entityDictionary.Remove(entityDictionary.Single(d => Object.Equals(d.Key, modelKey)).Key);
}
}
}
for (int i = 0; i < entityDictionary.Count; i++)
db.Entry(entityDictionary.ElementAt(i).Value).State = System.Data.Entity.EntityState.Deleted;
}
If you have a composite key, you'll have to modify the code a little, otherwise you can ignore the mapping with AutoMapper and then use the method above like so:
IEnumerable<Schedule> ScheduleEntities = db.Set<Schedule>().Where(s => s.ReportID == ReportID);
UpdateEntitySet<Schedule>(ScheduleViewModels, ScheduleEntities, "ScheduleID");

EF update the child relation of a relation

EF tracking confuses me. Here is a scenario that I am trying to achieve:
public class CentralPoint
{
public Guid ID { get; set; }
public virtual BIDatabase BIDatabase { get; set; }
}
public class BIDatabase
{
public Guid ID { get; set; }
public Guid CentralPointID { get; set; }
public virtual CentralPoint CentralPoint { get; set; }
public Guid ConnectionID { get; set; }
public virtual Connection Connection { get; set; }
}
public class Connection
{
public Guid ID { get; set; }
public string Username { get; set; }
public string Password { get; set; }
}
These are my entity models. I am having a one-one relationship between CentralPoint and BIDatabase entities, also a one-one relationship between BIDatabase and Connection entities. Obviously there is a separate table for each of these entities.
Inside the controller I am updating the BIDatabase property of the CentralPoint with a new instance
centralPoint.BIDatabase = biDatabase;
Here is the controller part:
public async Task<IActionResult> AddBIDatabaseAsync(Guid cpId, BIDatabase biDatabase)
{
// context is available through Dependency Injection (.net core)
var centralPoint = _context.CentralPoint.Where(cp => cp.ID == cpId)
.Include(cp => cp.BIDatabase)
.ThenInclude(biDb => biDb.Connection)
.FirstOrDefault();
centralPoint.BIDatabase = biDatabase;
await _context.SaveChangesAsync();
// more code ...
}
After this:
CentralPoint Table -> Remains Unchanged: Normal
BIDatabase Table -> Updated with new IDs: Normal
Connection Table -> // A new row is added instead of updating the old one
What I wanted is the connection entity to be updated and not added every time for the same database.

I think I see the issue.
When you replace centralPoint.BIDatabase = biDatabase; your new BIDatabase object probably doesnt have the Id linking it to Connection
Try mapping the fields you need onto the existing object instead of replacing it (or replace it, but map any Ids and existing fields that you want to be persisted through onto the new object first).

What code created this new biDatabase? Was it persisted to a dbContext prior to this method?
Your expectation around the BIDatabase and connection table is a bit suspicious. Given an existing CentralPoint /w BIDatabase /w Connection, if you "change" the CentralPoint's BIDatabase to a new one, the existing record is not updated, it is replaced. This means that the old record and it's associated connection would be removed, and a new BIDatabase /w a new Connection would be inserted. Assuming these entities are configured with DB generated keys:
Example:
CentralPoint(id:1) -> BIDatabase(id:1) -> Connection(id:1)
Create new BIDatabase (id:x) with new Connection (id:x) then:
CentralPoint.BIDatabase = newBIDatabase
BIDatabase(id:1) & Connection(id:1) are marked for deletion.
new BIDatabase & Connection will be persisted with new IDs when saved.
CentralPoint(id:1) -> BIDatabase(id:2) -> Connection(id:2)
If you want to replace the BIDatabase but keep the same connection ID/reference:
Create the new BIDatabase(id:x) /w Connection(id:x)
but before saving it to the context:
var centralPoint = _context.CentralPoint.Where(cp => cp.ID == cpId)
.Include(cp => cp.BIDatabase)
.ThenInclude(biDb => biDb.Connection)
.FirstOrDefault();
biDatabase.Connection = (centralPoint?.BIDatabase?.Connection) ?? biDatabase.Connection;
centralPoint.BIDatabase = biDatabase;
await _context.SaveChangesAsync();
What that extra statement does is look to preserve an existing connection already on the existing CentralPoint.BIDatabase by copying the reference over to the new BIDatabase. If the existing BIDatabase didn't have a connection (or the existing CP didn't have a BIDatabase) then the new connection created would be used. Provided you haven't saved the new BIDatabase to a dbContext prior to this code, the "new" Connection (id:x) will never get inserted where an existing one is substituted.

There were a couple of mistakes I was doing. I am detailing them so it might be helpful to others.
First mistake (pointed out by #Steveland83)
centralPoint.BIDatabase = biDatabase;
Since the CentralPoint entity is being tracked by the context (DbContext) we cannot simply replace a property by another. We need to modify the property by copying values.
So the following should be done instead
_context.Entry(centralPoint.BIDatabase).CurrentValues.SetVal‌​ues(biDatabase);
Second mistake
With the fix above, I was expecting the context to track all property changes in the centralPoint.BIDatabase and update those as well by itself (In my case the Connection property eg. centralPoint.BIDatabase.Connection)
However unfortunately this does not happen for non primitive types. You have to tell the context explicitly which of the non-primitive properties changed.
Here is the second fix
_context.Entry(centralPoint.BIDatabase).CurrentValues.SetVal‌​ues(biDatabase);
_context.Entry(centralPoint.BIDatabase.Connection).CurrentValues.SetVal‌​ues(biDatabase.Connection);
This Updates the BIDatabase and the Connection tables with the changes.

Updating many-to-many relationships with a generic repository

I have a database context with lazy loading disabled. I am using eager loading to load all of my entities. I cannot update many to many relationships.
Here's the repository.
public class GenericRepository<TEntity> : IGenericRepository<TEntity>
where TEntity : class
{
... other code here...
public virtual void Update(TEntity t)
{
Set.Attach(t);
Context.Entry(t).State = EntityState.Modified;
}
...other code here...
}
Here's the User model.
public partial class User
{
public User()
{
this.Locks = new HashSet<Lock>();
this.BusinessModels = new HashSet<BusinessModel>();
}
public int UserId { get; set; }
public string Username { get; set; }
public string Name { get; set; }
public string Phone { get; set; }
public string JobTitle { get; set; }
public string RecoveryEmail { get; set; }
public Nullable<double> Zoom { get; set; }
public virtual ICollection<Lock> Locks { get; set; }
public virtual ICollection<BusinessModel> BusinessModels { get; set; }
}
If I modify the business models collection, it does not save the business models collection although I have attached the entire entity.
Worker.UserRepository.Update(user);
I'm not sure what is going on. I don't want to break my generic repository/unit of work pattern just to update many-to-many relationships.
Edit 2: I've got this working...but it is extremely different from the pattern that I'm going for. Having hard implementations means I will need to create a method for each type that has a many to many relationship. I am investigating now to see if I can make this a generic method.
Edit 3: So the previous implementation I had did not work like I thought it would. But now, I have a slightly working implementation. If someone would please help me so I can move on from this, I will love you forever.
public virtual void Update(TEntity updated,
IEnumerable<object> set,
string navigationProperty,
Expression<Func<TEntity, bool>> filter,
Type propertyType)
{
// Find the existing item
var existing = Context.Set<TEntity>().Include(navigationProperty).FirstOrDefault(filter);
// Iterate through every item in the many-to-many relationship
foreach (var o in set)
{
// Attach it if its unattached
if (Context.Entry(o).State == EntityState.Detached)
// Exception "an object with the same key already exists"
// This is due to the include statement up above. That statement
// is necessary in order to edit the entity's navigation
// property.
Context.Set(propertyType).Attach(o);
}
// Set the new value on the navigation property.
Context.Entry(existing).Collection(navigationProperty).CurrentValue = set;
// Set new primitive property values.
Context.Entry(existing).CurrentValues.SetValues(updated);
Context.Entry(existing).State = EntityState.Modified;
}
I then call it like this:
Worker.UserRepository.Update(user, user.BusinessModels, "BusinessModels", i => i.UserId == user.UserId, typeof (BusinessModel));
Extremely messy, but it lets me update many-to-many relationships with generics. My big problem is the exception when I go to attach new values that already exist. They're already loaded because of the include statement.
This works:
This doesn't:

After many painful hours, I have finally found a way to update many-to-many relationships with a completely generic repository. This will allow me to create (and save) many different types of entities without creating boilerplate code for each one.
This method assumes that:
Your entity already exists
Your many to many relationship is stored in a table with a composite key
You are using eager loading to load your relationships into context
You are using a unit-of-work/generic repository pattern to save your entities.
Here's the Update generic method.
public virtual void Update(Expression<Func<TEntity, bool>> filter,
IEnumerable<object> updatedSet, // Updated many-to-many relationships
IEnumerable<object> availableSet, // Lookup collection
string propertyName) // The name of the navigation property
{
// Get the generic type of the set
var type = updatedSet.GetType().GetGenericArguments()[0];
// Get the previous entity from the database based on repository type
var previous = Context
.Set<TEntity>()
.Include(propertyName)
.FirstOrDefault(filter);
/* Create a container that will hold the values of
* the generic many-to-many relationships we are updating.
*/
var values = CreateList(type);
/* For each object in the updated set find the existing
* entity in the database. This is to avoid Entity Framework
* from creating new objects or throwing an
* error because the object is already attached.
*/
foreach (var entry in updatedSet
.Select(obj => (int)obj
.GetType()
.GetProperty("Id")
.GetValue(obj, null))
.Select(value => Context.Set(type).Find(value)))
{
values.Add(entry);
}
/* Get the collection where the previous many to many relationships
* are stored and assign the new ones.
*/
Context.Entry(previous).Collection(propertyName).CurrentValue = values;
}
Here's a helper method I found online which allows me to create generic lists based on whatever type I give it.
public IList CreateList(Type type)
{
var genericList = typeof(List<>).MakeGenericType(type);
return (IList)Activator.CreateInstance(genericList);
}
And from now on, this is what calls to update many-to-many relationships look like:
Worker.UserRepository.Update(u => u.UserId == user.UserId,
user.BusinessModels, // Many-to-many relationship to update
Worker.BusinessModelRepository.Get(), // Full set
"BusinessModels"); // Property name
Of course, in the end you will need to somewhere call:
Context.SaveChanges();
I hope this helps anyone who never truly found how to use many-to-many relationships with generic repositories and unit-of-work classes in Entity Framework.

#dimgl Your solution worked for me. What I've done in addition was to replace the hard-coded type and name of the primaryKey with dynamically retrieved ones:
ObjectContext objectContext = ((IObjectContextAdapter)context).ObjectContext;
ObjectSet<TEntity> set = objectContext.CreateObjectSet<TEntity>();
IEnumerable<string> keyNames = set.EntitySet.ElementType.KeyMembers.Select(k => k.Name);
var keyName = keyNames.FirstOrDefault();
var keyType = typeof(TEntity).GetProperty(keyName).PropertyType
foreach (var entry in updatedSet
.Select(obj =>
Convert.ChangeType(obj.GetType()
.GetProperty(keyName)
.GetValue(obj, null), keyType))
.Select(value => context.Set<TEntity>().Find(value)))
{
values.Add(entry);
}
Like this your code won't depend on the Entity key's name and type.

My class is creating entries in the database and I want it to stop

I'm working on a project using entity framework and code first. Here are my shortened classes
public class BenefitsForm : IAnnualForm, IAuditable
{
public BenefitsUser UserInfo { get; set; }
public CoverageLevel Medical { get; set; }
}
public class MedicalPlan : IHealthPlan
{
public int Id { get; set; }
public virtual IList<CoverageLevel> CoverageLevels { get; set; }
}
public class CoverageLevel
{
public int Id { get; set; }
public virtual MedicalPlan MedicalPlan { get; set; }
}
There are 4 coverage levels in each MedicalPlan. I already have my coverage levels and medical plans made in the database. However, when I create my BenefitsForm, it creates duplicate entries for the classes (I already have them in the database). How can I prevent it from doing this? Here is a small code snippet to show how it happens.
BenefitsForm form = new BenefitsForm() { UserInfo = new BenefitsUser() };
using(var repo = new CoverageLevelRepository())
{
form.Medical = repo.Retrieve(new NumericKey(formId))); //this retrieves the coveragelevel with the id I want.
}
formRepository.Create(form); // this creates a duplicate med plan and 4 duplicate coverage levels.
formRepository.SaveChanges();

I think because you're retrieving the Medical field from a different context than the one you're saving in -- repo vs. formRepository; formRepository isn't tracking the object created by repo, so it assumes that it's a new object, and thus creates a duplicate entry. For performance reasons, I don't believe Entity Framework will go and insert existence checks for you -- tracking is handled internally by the object context itself; each object is bound to a single object context. Try using the same repository to retrieve the MedicalPlan and write back the new BenefitsForm, and you shouldn't have duplicates.
BenefitsForm form = new BenefitsForm() { UserInfo = new BenefitsUser() };
using(var repo = new Repository())
{
form.Medical = repo.Retrieve(new NumericKey(formId))); //this retrieves the coveragelevel with the id I want.
repo.Create(form); // this creates a duplicate med plan and 4 duplicate coverage levels.
repo.SaveChanges();
}

Instead of formRepository.SaveChanges() please try with to use the SaveChanges with the SaveOptions Enum
Example:
ObjectContext.SaveChanges(
System.Data.Objects.SaveOptions.DetectChangesBeforeSave
);
Please see link for more information http://msdn.microsoft.com/en-us/library/dd395500.aspx

It's possible that using IList<...> instead of ICollection<...> for your one-to-many association is causing it to malfunction. Try changing that. Other than that, it may be code within your CoverageLevelRepository that you did not post. For more info on associations, see this guide