0

这是我尝试执行的查询：

var contests = await _dbContext.Contests.Include(o => o.Winner)
                .Where(o=>o.Ended!=null)
                .Select(c => new 
                {
                    Contest = c,
                    Strings = _dbContext.ContestCountryStrings.Where(o=>o.ContestId==c.Id && (o.Country.Equals(language) || o.Country.Equals("Default"))).ToList()
                }).Take(3).ToListAsync();

这些是实体：

[Table("Contests")]
public class Contest
{
    public int Id { get; set; }
    
    public DateTime DueTo { get; set; }
    
    public uint DurationInHours { get; set; }
    public DateTime? Started { get; set; }
    public DateTime? Ended { get; set; }
    
    public int? WinnerId { get; set; }
    public User Winner { get; set; }
    
    public bool Recurrent { get; set; }
    public string ImageUrl { get; set; }
}

[Table("ContestCountryStrings")]
public class ContestCountryString
{
    public int Id { get; set; }
    public int ContestId { get; set; }
    public Contest Contest { get; set; }
    public string Country { get; set; }
    public string Title { get; set; }
    public string Description { get; set; }
}

执行时我得到一个这样的异常：

失败：Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1] 执行请求时发生未处理的异常。System.InvalidOperationException：使用错误的属性名称调用 EF.Property。在 Microsoft.EntityFrameworkCore.Query.RelationalSqlTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) 在 System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor) 在 System.Linq.Expressions.ExpressionVisitor.Visit(Expression node) 在 Microsoft.EntityFrameworkCore.Query.RelationalSqlTranslatingExpressionVisitor .VisitBinary(BinaryExpression binaryExpression) 在 Pomelo.EntityFrameworkCore.MySql.Query.ExpressionVisitors.Internal.MySqlSqlTranslatingExpressionVisitor.VisitBinary(BinaryExpression binaryExpression) 在 System.Linq.Expressions.BinaryExpression。
在 Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) 在 Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) 在 System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor) 在 System.Linq.Expressions.ExpressionVisitor .Visit(Expression node) at Microsoft.EntityFrameworkCore.Query.QueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) at Microsoft.EntityFrameworkCore.Query.RelationalQueryableMethodTranslatingExpressionVisitor.VisitMethodCall(MethodCallExpression methodCallExpression) at System.Linq.Expressions.MethodCallExpression.Accept(ExpressionVisitor visitor) at System .Linq。Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult]（表达式查询）的 Expressions.ExpressionVisitor.Visit（表达式节点）Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult]（表达式查询，布尔异步）在 Microsoft.EntityFrameworkCore .Query.Internal.QueryCompiler.CompileQueryCore[TResult]（IDatabase 数据库，表达式查询，IModel 模型，布尔异步）在 Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0 上的 CompileQueryCore[TResult]（IDatabase 数据库、表达式查询、IModel 模型、布尔异步）Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass12_0 上的 CompileQueryCore[TResult]（IDatabase 数据库、表达式查询、IModel 模型、布尔异步）1.<ExecuteAsync>b__0() at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQueryCore[TFunc](Object cacheKey, Func1 编译器）在 Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func 1 compiler) at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.ExecuteAsync[TResult](Expression query, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.ExecuteAsync[TResult](Expression expression, CancellationToken cancellationToken) at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable1.GetAsyncEnumerator(CancellationToken cancelToken) 在 System.Runtime.CompilerServices.ConfiguredCancelableAsyncEnumerable1.GetAsyncEnumerator() at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToListAsync[TSource](IQueryable1 来源，CancellationToken 取消令牌）在 MoneyAppBackend.Controllers.ContestsController._GetLas10PastEvents（EventType 类型，字符串语言）在 /Users/juanjoseduran/Documents/Development/Projects/dotnet/MoneyAppBackend/MoneyAppBackend/Controllers/ContestsController.cs：在 MoneyAppBackend 的第 106 行。 Controllers.ContestsController.GetAll(EventType type, String lang, String uuid) in /Users/juanjoseduran/Documents/Development/Projects/dotnet/MoneyAppBackend/MoneyAppBackend/Controllers/ContestsController.cs:line 57 at lambda_method(Closure, Object) at Microsoft .Extensions.Internal.ObjectMethodExecutorAwaitable.Awaiter.GetResult() at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(IActionResultTypeMapper 映射器，ObjectMethodExecutor 执行器，对象控制器，Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.g__Awaited|10_0（ControllerActionInvoker 调用程序，任务 lastTask，State next, Scope 范围，对象状态，Boolean isCompleted) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) 在 Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync() --- 在 Microsoft.AspNetCore.Mvc.Infrastructure 中从先前引发异常的位置结束堆栈跟踪。Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.g__Awaited|19_0（ResourceInvoker 调用程序，任务 lastTask，下一个状态，作用域范围，对象状态，布尔 isCompleted）。Microsoft 的 ResourceInvoker 调用程序，任务任务，IDisposable 范围） .AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger) 在 Microsoft.AspNetCore.Builder.Extensions.MapMiddleware.Invoke(HttpContext context) 在 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context)IDisposable 范围）在 Microsoft.AspNetCore.Builder.Extensions.MapMiddleware.Invoke（HttpContext 上下文）在 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware 的 Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0（端点端点，任务 requestTask，ILogger 记录器）。调用（HttpContext 上下文）IDisposable 范围）在 Microsoft.AspNetCore.Builder.Extensions.MapMiddleware.Invoke（HttpContext 上下文）在 Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware 的 Microsoft.AspNetCore.Routing.EndpointMiddleware.g__AwaitRequestTask|6_0（端点端点，任务 requestTask，ILogger 记录器）。调用（HttpContext 上下文）

如果我删除 Take 呼叫，它可以正常工作。

4

1 回答 1

0

就像@NetMage说的，既然你要的数据take是Contest类型数据，如果你把take后面的Selectis对后面的数据进行操作，Select得到的数据不会是Contest类型的，会导致异常。

您可以更改您的代码，如下所示：

var contests = await _dbContext.Contests.Include(o => o.Winner)
        .Where(o=>o.Ended!=null).Take(3)
        .Select(c => new 
        {
            Contest = c,
            Strings = _dbContext.ContestCountryStrings.Where(o=>o.ContestId==c.Id && (o.Country.Equals(language) || o.Country.Equals("Default"))).ToList()
        }).ToListAsync();
于 2020-11-16T14:31:50.827 回答