entity framework一对多的关系

我的EF查询需要大约3秒来获取10个玩家，因为它获取了另一个表的所有500k +行，而不是我需要的几个。

这是PlayerEntity：

namespace RocketLeagueStats.Database.Entities { [Table("players", Schema = "public")] public class PlayerEntity { [Key] [Column("id")] public int Id { get; set; } [Column("unique_id")] public string UniqueId { get; set; } [Column("display_name")] public string DiplayName { get; set; } [Column("platform_id")] [JsonIgnore] public int PlatformId { get; set; } [ForeignKey("PlatformId")] public PlatformEntity Platform { get; set; } [Column("avatar")] public string Avatar { get; set; } public PlayerStatsEntity Stats { get; set; } public List Ranks { get; set; } [Column("last_requested")] public DateTime LastRequested { get; set; } [Column("created_at")] public DateTime CreatedAt { get; set; } [Column("updated_at")] public DateTime UpdatedAt { get; set; } } } 

这是PlayerRankedEntity：

 namespace RocketLeagueStats.Database.Entities { [Table("player_ranked", Schema = "public")] public class PlayerRankedEntity { [ForeignKey("Player")] [Column("player_id")] [JsonIgnore] public int PlayerId { get; set; } [Column("season_id")] [JsonIgnore] public int SeasonId { get; set; } [Column("playlist_id")] [JsonIgnore] public int PlaylistId { get; set; } [Column("matches_played")] public int MatchesPlayed { get; set; } [Column("rank_points")] public int RankPoints { get; set; } [Column("tier")] public int Tier { get; set; } [Column("division")] public int Division { get; set; } public PlayerEntity Player { get; set; } } } 

这是PlayerStatsEntity：

 namespace RocketLeagueStats.Database.Entities { [Table("player_stats", Schema = "public")] public class PlayerStatsEntity { [Key, ForeignKey("Player")] [Column("player_id")] [JsonIgnore] public int PlayerId { get; set; } [Column("wins")] public int Wins { get; set; } [Column("goals")] public int Goals { get; set; } [Column("mvps")] public int Mvps { get; set; } [Column("saves")] public int Saves { get; set; } [Column("shots")] public int Shots { get; set; } [Column("assists")] public int Assists { get; set; } public PlayerEntity Player { get; set; } } } 

这是我的DatabaseContext.OnModelCreating方法：

 protected override void OnModelCreating(ModelBuilder modelBuilder) { modelBuilder.Entity() .HasKey(k => new { k.PlayerId, k.SeasonId, k.PlaylistId }); } 

这是需要3秒才能完成的代码（如果我删除’.Include（x => x.Ranks）’只需要几毫秒）：

 using (var database = new DatabaseContext()) { var serviceProvider = database.GetInfrastructure(); var loggerFactory = serviceProvider.GetService(); loggerFactory.AddNLog(); var stopwatch = Stopwatch.StartNew(); var players = database.Players .Include(x => x.Ranks) .Take(10) .ToArray(); Console.WriteLine($"Took {stopwatch.ElapsedMilliseconds}ms to fetch {players.Length} players"); } 

这是输出，请注意它生成两个查询而不是一个：

 2016-10-31 22:50:18.6416 INFO Executed DbCommand (8ms) [Parameters=[@__p_0='?'], CommandType='Text', CommandTimeout='30'] SELECT "x"."id", "x"."avatar", "x"."created_at", "x"."display_name", "x"."last_requested", "x"."platform_id", "x"."unique_id", "x"."updated_at" FROM "public"."players" AS "x" ORDER BY "x"."id" LIMIT @__p_0 2016-10-31 22:50:18.7128 INFO Executed DbCommand (0ms) [Parameters=[@__p_0='?'], CommandType='Text', CommandTimeout='30'] SELECT "p"."player_id", "p"."season_id", "p"."playlist_id", "p"."division", "p"."matches_played", "p"."rank_points", "p"."tier" FROM "public"."player_ranked" AS "p" WHERE EXISTS ( SELECT 1 FROM "public"."players" AS "x" WHERE "p"."player_id" = "x"."id" LIMIT @__p_0) ORDER BY "p"."player_id" Took 3991ms to fetch 10 players 

我认为我搞砸了某处的关系，导致它选择所有行。 但我不知道我搞砸了什么。

我该如何解决这个问题，我的属性还有其他问题吗？

我正在使用Microsoft.EntityFrameworkCore v1.0.1。

编辑：如果我在查询中使用.OrderBy(x => x.CreatedAt)或.Where(x => x.DiplayName.Contains("mike")) ，它会更快。

生成的查询：

 2016-11-01 00:14:15.9638 INFO Executed DbCommand (24ms) [Parameters=[@__p_0='?'], CommandType='Text', CommandTimeout='30'] SELECT "x"."id", "x"."avatar", "x"."created_at", "x"."display_name", "x"."last_requested", "x"."platform_id", "x"."unique_id", "x"."updated_at" FROM "public"."players" AS "x" ORDER BY "x"."created_at", "x"."id" LIMIT @__p_0 2016-11-01 00:14:16.0972 INFO Executed DbCommand (44ms) [Parameters=[@__p_0='?'], CommandType='Text', CommandTimeout='30'] SELECT "p"."player_id", "p"."season_id", "p"."playlist_id", "p"."division", "p"."matches_played", "p"."rank_points", "p"."tier" FROM "public"."player_ranked" AS "p" INNER JOIN ( SELECT DISTINCT "x"."created_at", "x"."id" FROM "public"."players" AS "x" ORDER BY "x"."created_at", "x"."id" LIMIT @__p_0 ) AS "x0" ON "p"."player_id" = "x0"."id" ORDER BY "x0"."created_at", "x0"."id" Took 314ms to fetch 10 players 

Answer 1

EF Core目前是一场噩梦。

您可以尝试以下解决方法（但如果您问我，最好切换回EF6）。

代替：

 var players = database.Players .Include(x => x.Ranks) .Take(10) .ToArray(); 

使用：

 var players = database.Players .Take(10) .ToArray(); var playerIds = players.Select(p => p.Id); database.PlayerRanks.Where(r => playerIds.Contains(r.PlayerId)).Load(); 

它应该产生与Include相同的效果。