EF - Unable to determine the relationship

Question

I'm making a fantasy game application. Right now a team can have multiple players, but also multiple users (like league). When i try to add the a collection to the team table, i get the following error (see below). I tried to find the solution online and it seems that this problem is causes by a many to many relationship. However, i don't see how that is possible. A team can have many users, but a user can only have one team. The solution was to create a join table, but why would i create a column on each table to point to a join table that contains the data, when i could just have the column on each table join to the other table? Does anyone know what is causing this error and how to fix it?

System.InvalidOperationException: Unable to determine the relationship represented by navigation property 'Team.Manager' of type 'User'. Either manually configure the relationship, or ignore this property from the model.    at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.PropertyMappingValidationConvention.Apply(InternalModelBuilder modelBuilder)
    at Microsoft.EntityFrameworkCore.Metadata.Conventions.Internal.ConventionDispatcher.OnModelBuilt(InternalModelBuilder modelBuilder)
   at Microsoft.EntityFrameworkCore.Infrastructure.ModelSource.CreateModel(DbContext context, IConventionSetBuilder conventionSetBuilder, IModelValidator validator)
    at System.Collections.Concurrent.ConcurrentDictionary`2.GetOrAdd(TKey key, Func`2 valueFactory)
    at Microsoft.EntityFrameworkCore.Internal.DbContextServices.CreateModel()
    at Microsoft.EntityFrameworkCore.Internal.LazyRef`1.get_Value() 
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitScoped(ScopedCallSite scopedCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetService[T](IServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitConstructor(ConstructorCallSite constructorCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceLookup.CallSiteRuntimeResolver.VisitTransient(TransientCallSite transientCallSite, ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProvider.<>c__DisplayClass16_0.<RealizeService>b__0(ServiceProvider provider)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService(IServiceProvider provider, Type serviceType)
   at Microsoft.Extensions.DependencyInjection.ServiceProviderServiceExtensions.GetRequiredService[T](IServiceProvider provider)
   at Microsoft.EntityFrameworkCore.Design.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
    at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.Execute(CommonOptions commonOptions, String name, String outputDir, String context, String environment, Action`1 reporter)
    at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.<>c__DisplayClass0_0.<Configure>b__0()
    at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args) 
   at Microsoft.EntityFrameworkCore.Tools.Cli.Program.Main(String[] args)
 Unable to determine the relationship represented by navigation property 'Team.Manager' of type 'User'. Either manually configure the relationship, or ignore this property from the model. 

Team.cs

public class Team
{
    [Key]
    public int ID { get; set; }
    public int ManagerID { get; set; }
    public string Name { get; set; }

    [ForeignKey("ManagerID")]
    public virtual User Manager { get; set; }
    public virtual ICollection<Player> Players { get; set; }
    // Unable to determine the relationship represented by navigation property 'Team.Manager' of type 'User'
    public virtual ICollection<User> TeamMebers { get; set; }


    public Team()
    {
        TeamMebers = new List<User>();
        Players = new List<Player>();
    }
}

User.cs

public class User
{
    [Key]
    public int ID { get; set; }
    public int? TeamID { get; set; }
    public string UserName { get; set; }
    public string Name { get; set; }
    public bool ShowAsPm { get; set; }
    public string Deactiviated { get; set; }

    [ForeignKey("TeamID")]
    public virtual Team Team { get; set; }
    // How many hours they played 
    public virtual ICollection<Log> Hours { get; set; }

    public User()
    {
        Hours = new List<Log>();
    }
}

Log.cs

public class Log
{
    [Key]
    public int ID { get; set; }
    public int? GameID { get; set; }
    public int? ResultID { get; set; }
    public int? UserID { get; set; }

    public string SmNumber { get; set; }
    public decimal? Duration { get; set; }
    public DateTime LogDate { get; set; }

    [ForeignKey("GameID")]
    public virtual Game Game { get; set; }
    [ForeignKey("ResultID")]
    public virtual GameResult Result { get; set; }
    [ForeignKey("UserID")]
    public virtual User User { get; set; }

    public Log() { }
}

Context.cs

protected override void OnModelCreating(ModelBuilder builder)
{
     //builder.Entity<Team>().HasMany(t => t.TeamMebers).WithOne(u => u.Team).HasForeignKey(u => u.ID);
    //builder.Entity<User>().HasOne(u => u.Team).WithMany(t => t.TeamMebers).HasForeignKey(t => t.ID);
    builder.Entity<Team>().ToTable("Teams");
    builder.Entity<User>().ToTable("Users");
    builder.Entity<Log>().ToTable("Logs");
}

Update

protected override void OnModelCreating(ModelBuilder builder)
{
    builder.Entity<Team>().ToTable("Teams");
    builder.Entity<User>().ToTable("Users");
    builder.Entity<User>().HasOne(u => u.Team).WithMany(u => u.TeamMebers);
    builder.Entity<Log>().ToTable("Logs");
}

Exception

System.InvalidOperationException: The current CSharpHelper cannot scaffold literals of type 'System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]'. Configure your services to use one that can.    at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpHelper.UnknownLiteral(Object value)
    at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateAnnotation(IAnnotation annotation, IndentedStringBuilder stringBuilder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityTypeAnnotations(IEntityType entityType, IndentedStringBuilder stringBuilder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityType(String builderName, IEntityType entityType, IndentedStringBuilder stringBuilder)
    at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.GenerateEntityTypes(String builderName, IReadOnlyList`1 entityTypes, IndentedStringBuilder stringBuilder) 
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpSnapshotGenerator.Generate(String builderName, IModel model, IndentedStringBuilder stringBuilder)
   at Microsoft.EntityFrameworkCore.Migrations.Design.CSharpMigrationsGenerator.GenerateMetadata(String migrationNamespace, Type contextType, String migrationName, String migrationId, IModel targetModel)
   at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace)
    at Microsoft.EntityFrameworkCore.Design.MigrationsOperations.AddMigration(String name, String outputDir, String contextType)
    at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.Execute(CommonOptions commonOptions, String name, String outputDir, String context, String environment, Action`1 reporter) 
    at Microsoft.EntityFrameworkCore.Tools.Cli.MigrationsAddCommand.<>c__DisplayClass0_0.<Configure>b__0()
    at Microsoft.Extensions.CommandLineUtils.CommandLineApplication.Execute(String[] args) 
   at Microsoft.EntityFrameworkCore.Tools.Cli.Program.Main(String[] args)
 The current CSharpHelper cannot scaffold literals of type 'System.Collections.Immutable.ImmutableSortedDictionary`2[System.Reflection.PropertyInfo,System.Type]'. Configure your services to use one that can. 

Answer 1

The 'problem' with your situation is explained in the exception you are getting:

Unable to determine the relationship represented by navigation property 'Team.Manager' of type 'User'. Either manually configure the relationship, or ignore this property from the model.

The solution, as the message suggests is manually defining this relationship.

builder.Entity<User>().HasOne(u => u.Team).WithMany(u => u.TeamMembers);

However this does not solve your problem completely, because this does not resolve the issue with one of the members being a Manager.

A better solution would be to use the following intermediate class, which would handle the relationship, while also marking one of the members as the Manager. This still does not resolve the issue of a single Manager constraint per Team, but it gets a lot closer.

public class TeamMember {
    public int MemberId {get;set;}
    public int TeamId {get;set;}
    public bool IsManager {get;set;}

    public virtual User Member {get;set;}
    public virtual Team Team {get;set;}
}
//Either add an ID or use fluent API to define the key to be a combination of player/teamid