我有一个实体框架查询，如下所示：
public object GetMatchupByVideoId(int id)
{
var videoMatchup = _DBContext.Videos
.Where(v => v.VideoID == id)
.Select(v => new {
id = v.MatchupID,
players = v.Matchup.Players.Select(mp => new
{
character = new {
name = mp.Character.Name,
votes = v.Matchup.MatchupVotes
.Where(mv => mv.CharacterID == mp.CharacterID)
},
outcome = mp.Outcome
})
});
return videoMatchup;
}
这个查询基本上给了我一个角色与各自投票的对比。如果您查看votes属性，您会看到它仅根据CharacterID过滤掉投票。这符合我的预期。
但是，我想更进一步，实际得到每个角色的投票数。所以，如果我将查询更改为以下内容：
public object GetMatchupByVideoId(int id)
{
var videoMatchup = _DBContext.Videos
.Where(v => v.VideoID == id)
.Select(v => new {
id = v.MatchupID,
players = v.Matchup.Players.Select(mp => new
{
character = new {
name = mp.Character.Name,
votes = v.Matchup.MatchupVotes
.Where(mv => mv.CharacterID == mp.CharacterID)
.Count()
},
outcome = mp.Outcome
})
});
return videoMatchup;
}
在.Count()的查询末尾添加votes，我收到错误消息：
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[1]
Request starting HTTP/1.1 GET http://localhost:5000/api/videos/1/matchup application/json
info: Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker[1]
Executing action method Mindgame.Controllers.VideosController.GetMatchupByVideoId (mindgame-api) with arguments (1) - ModelState is Valid
info: Microsoft.AspNetCore.Mvc.Internal.ObjectResultExecutor[1]
Executing ObjectResult, writing value Microsoft.AspNetCore.Mvc.ControllerContext.
fail: Microsoft.AspNetCore.Server.Kestrel[13]
Connection id "0HL0OILHK80GT": An unhandled exception was thrown by the application.
Microsoft.Data.Sqlite.SqliteException: SQLite Error 1: 'no such column: v.Matchup.MatchupID'.
at Microsoft.Data.Sqlite.Interop.MarshalEx.ThrowExceptionForRC(Int32 rc, Sqlite3Handle db)
at Microsoft.Data.Sqlite.SqliteCommand.ExecuteReader(CommandBehavior behavior)
at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.Execute(IRelationalConnection connection, String executeMethod, IReadOnlyDictionary`2 parameterValues, Boolean closeConnection)
at Microsoft.EntityFrameworkCore.Storage.Internal.RelationalCommand.ExecuteReader(IRelationalConnection connection, IReadOnlyDictionary`2 parameterValues)
at Microsoft.EntityFrameworkCore.Query.Internal.QueryingEnumerable.Enumerator.BufferlessMoveNext(Boolean buffer)
at Microsoft.EntityFrameworkCore.Query.QueryMethodProvider.<_ShapedQuery>d__3`1.MoveNext()
at System.Linq.Enumerable.WhereSelectEnumerableIterator`2.MoveNext()
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeObject(JsonWriter writer, Object value, JsonObjectContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.SerializeList(JsonWriter writer, IEnumerable values, JsonArrayContract contract, JsonProperty member, JsonContainerContract collectionContract, JsonProperty containerProperty)
at Newtonsoft.Json.Serialization.JsonSerializerInternalWriter.Serialize(JsonWriter jsonWriter, Object value, Type objectType)
at Newtonsoft.Json.JsonSerializer.SerializeInternal(JsonWriter jsonWriter, Object value, Type objectType)
at Microsoft.AspNetCore.Mvc.Formatters.JsonOutputFormatter.WriteObject(TextWriter writer, Object value)
at Microsoft.AspNetCore.Mvc.Formatters.JsonOutputFormatter.<WriteResponseBodyAsync>d__9.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResultAsync>d__32.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResultFilterAsync>d__31.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAllResultFiltersAsync>d__29.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeResourceFilterAsync>d__23.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at Microsoft.AspNetCore.Mvc.Internal.ControllerActionInvoker.<InvokeAsync>d__18.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Builder.RouterMiddleware.<Invoke>d__4.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Hosting.Internal.RequestServicesContainerMiddleware.<Invoke>d__3.MoveNext()
--- End of stack trace from previous location where exception was thrown ---
at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
at Microsoft.AspNetCore.Server.Kestrel.Internal.Http.Frame`1.<RequestProcessingAsync>d__2.MoveNext()
info: Microsoft.AspNetCore.Hosting.Internal.WebHost[2]
Request finished in 787.4541ms 200 application/json; charset=utf-8
此错误消息的兴趣点在于：
SQLite Error 1: 'no such column: v.Matchup.MatchupID'.
如果上一个查询在没有.Count()的情况下工作，我不确定为什么会出现此错误。此外，我在查询中根本没有使用v.Matchup.MatchupID。我只能想象这是底层SQL正在做的事情。
以下是Video，Player，＆＃39; Matchup , and MatchupVote`的模型：
public class Video
{
[JsonPropertyAttribute("id")]
public int VideoID { get; set; }
[ForeignKeyAttribute("Game")]
public int GameID { get; set; }
public Game Game { get; set; }
[ForeignKeyAttribute("Matchup")]
public int MatchupID { get; set; }
public Matchup Matchup { get; set; }
[ForeignKeyAttribute("User")]
public int UserID { get; set; }
public User User { get; set; }
public string YoutubeID { get; set; }
public string Description { get; set; }
public string Title { get; set; }
}
public class Player
{
[JsonPropertyAttribute("id")]
public int PlayerID { get; set; }
public int CharacterID { get; set; }
public Character Character { get; set; }
public Players.Outcomes Outcome { get; set; }
}
public class Matchup
{
[JsonPropertyAttribute("id")]
[Required]
public int MatchupID { get; set; }
public List<MatchupVote> MatchupVotes { get; set; }
public List<Player> Players { get; set; }
}
public class MatchupVote
{
[JsonPropertyAttribute("id")]
public int MatchupVoteID { get; set; }
[ForeignKeyAttribute("Character")]
public int CharacterID { get; set; }
[ForeignKeyAttribute("Matchup")]
public int MatchupID { get; set; }
public Matchup Matchup { get; set; }
}
所以，我的问题是，如何使用这样的.Count()方法计算我想要查询中每个字符的投票数？
我正在为此项目使用.NET Core和Entity Framework Core。
答案 0 :(得分：3)
以下是评论中的答案，以防任何人偶然发现这一点。
_DBContext.MatchupVotes.Where(mv => mv.CharacterID == mp.CharacterID).Count()
就性能而言，我认为它不会产生任何影响，因为底层SQL正在进行过滤的独特计数。如果你非常关心性能，我会查看分析器，但由于它是一个过滤计数，我认为不会有你遇到的性能影响。