Entity Framework mapping 2 one to many with existing DB and Model - entity-framework

Question

I have been trying to update a project of my with Entity Framework. I have an existing database and model, which after some work matched. With some more work, I managed to get the application to successfully read the data from the database. But when saving new data, the nightmare started.
In my data structure, I have 2 one-to-many relations, one between player and team and one between match and team. I have been trying many configurations (with [Key], foreign key, inverse property attributes) but I either get an error
Trying to cast List to team
or
no column found Match_id no column found Player_id
This is my code:
public class Match
{
//[Key]
//[DatabaseGenerated(DatabaseGeneratedOption.None)]
public string Id { get; set; }
//[Column("Date")]
public DateTime Date { get; set; }
public DateTime EndTime { get; set; }
[NotMapped]
public bool Remove { get; set; }
//[InverseProperty("Match")]
[ForeignKey("MatchId")]
public virtual ICollection<Team> Teams { get; set; }
public int WinningTeamId { get; set; }
public MatchType MatchType { get; set; }
public string Source { get; internal set; }
public Match()
{
WinningTeamId = -1;
this.Teams = new List<Team>();
this.EndTime = (DateTime)SqlDateTime.MinValue;
}
}
public class Team
{
public int TeamId { get; set; }
[NotMapped]
public int RatingChange { get; set; }
[Key()]
[Column("PlayerId", Order = 2)]
[DatabaseGenerated(DatabaseGeneratedOption.None)]
public virtual Player Player { get; set; }
[Column(Order = 1)]
[Key()]
//[DatabaseGenerated(DatabaseGeneratedOption.None)]
public string MatchId { get; set; }
[ForeignKey("MatchId")]
public virtual Match Match { get; set; }
[NotMapped]
public int Rating { get; set; }
public Team()
{
}
}
public class Player
{
public string name { get; set; }
public int PastatsId { get; set; }
public string UberId { get; set; }
//[ForeignKey("PlayerId")]
//[InverseProperty("Player")]
public virtual ICollection<Team> Teams { get; set; }
//[Key()]
public int Id { get; set; }
}
To save the new matches, I first save the players to prevent conflicts there:
public void Save(IEnumerable<Match> matches)
{
foreach (var match in matches)
{
foreach (var team in match.Teams)
{
var entry = Entry(team.Player);
if (entry.State == EntityState.Detached)
{
var localplayer = Players.Local.FirstOrDefault(x => x.UberId == team.Player.UberId);
if (localplayer == null)
{
this.Players.Add(team.Player);
team.Player = entry.Entity;
}
else
{
team.Player = localplayer;
}
}
else
{
Entry(team.Player).State = EntityState.Modified;
}
}
}
SaveChanges();
foreach (var match in matches)
{
if (Matches.Find(match.Id) != null)
{
continue;
}
if (Entry(match).State == EntityState.Detached)
{
this.Matches.Add(match);
}
}
SaveChanges();
}
How to do this mapping with an existing database and code?
Any insight will be gratefully appreciated.