Entity framework navigation property is null

Question

I have two models using Entity Framework.

public class Player { public int PlayerId { get; set; } public string Name { get; set; } public string Sex { get; set; } public string Plays { get; set; } public string FavouriteSurface { get; set; } } public class SinglesMatch { public int SinglesMatchId { get; set; } public int Player1Id { get; set; } public int Player2Id { get; set; } public int PlayerIdWinner { get; set; } public DateTime Date { get; set; } public string Venue { get; set; } public string Score { get; set; } public List<Player> Players { get; set; } }

I am using the below code to attempt to display the Name of the player, based on the PlayerId in the SinglesMatch model matching the PlayerID from the Player model.

 @foreach (var item in @Model) { <ul id="Players" class="bg-success"></ul> <br/> <h3>Date - @Html.DisplayFor(@modelItem => item.Date)</h3> <li>Venue - @Html.DisplayFor(@modelItem => item.Venue)</li> <li>Player 1 - @Html.DisplayFor(@modelItem => item.Players.First(p => p.PlayerId == item.Player1Id).Name)</li> <li>Player 2 - @Html.DisplayFor(@modelItem => item.Players.First(p => p.PlayerId == item.Player2Id).Name)</li> <li>Score- @Html.DisplayFor(@modelItem => item.Score)</li> }

Upon debugging, the navigation property is always showing as null when the model is retrieved from my repository.

Am I using the navigation property in the correct fashion ? is there a problem with my query ?

Edit to include DbContext:

 public TennisTrackerContext() : base("name=TennisTrackerContext") { } public DbSet<Player> Players { get; set; } public DbSet<PlayerRecord> PlayerRecords { get; set; } public DbSet<SinglesMatch> SinglesMatches { get; set; } public DbSet<DoublesMatch> DoublesMatches { get; set; } public DbSet<Venue> Venues { get; set; } }

}

MIKE · Accepted Answer · 2015-12-24 18:25:43Z

You need to add a bridge table. Sql will create this automatically but you won't have access to the variables unless you create it in c#.

public class Player { public int PlayerId { get; set; } public string Name { get; set; } public string Sex { get; set; } public string Plays { get; set; } public string FavouriteSurface { get; set; } List<PlayerInMatch> Matches { get; set; } public Player() { Matches = new List<PlayerInMatch>(); } } public class PlayerInMatch { public int Id { get; set; } public int PlayerId { get; set; } [ForeignKey("PlayerId")] public Player Player { get; set; } public int SinglesMatchId { get; set; } [ForeignKey("SinglesMatchId")] public SinglesMatch SinglesMatch { get; set; } } public class SinglesMatch { public int SinglesMatchId { get; set; } public int PlayerIdWinner { get; set; } public DateTime Date { get; set; } public string Venue { get; set; } public string Score { get; set; } public List<PlayerInMatch> Players { get; set; } public SinglesMatch() { Players = new List<PlayerInMatch>(); } } static void Main(string[] args) { var match = new SinglesMatch(); match.Players.Select(c => c.Player.Name); }

Correct. The OP's model needs refactoring to get this right. This may be a way to do it.

Alexander Derck · Accepted Answer · 2015-12-23 13:37:11Z

You need to make your navigation property virtual to enable lazy/eager loading:

public class SinglesMatch { public int SinglesMatchId { get; set; } public int Player1Id { get; set; } public int Player2Id { get; set; } public int PlayerIdWinner { get; set; } public DateTime Date { get; set; } public string Venue { get; set; } public string Score { get; set; } public virtual List<Player> Players { get; set; } }

Also, did you define the relationship between SinglesMatch and Singles in fluent api?

EDIT: I see you don't have any relations mapped through annotations or fluent api whatsoever, I suggest you take a look at this:

https://msdn.microsoft.com/en-us/data/jj591617.aspx

Hi, I thought this may be the case so switched to a virtual, but I then got the error, receiveTemplates can be used only with field access, property access, single-dimension array index, or single-parameter custom indexer expressions. Also, what do you mean by define the relationship in fluent api ? many thanks
Can you edit your question to include your DbContext? Your fluent api is in there

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