EF Core 6 – ToQueryString() 在使用 FromSqlRaw 创建的查询上抛出异常“序列不包含任何元素”

Question

这是我第一次使用 EF Core 的查询模式。 因为我的带参数的大型查询也引发了异常“序列不包含任何元素”。

System.InvalidOperationException
  HResult=0x80131509
  Message=Sequence contains no elements
  Source=System.Linq
  StackTrace:
   at System.Linq.ThrowHelper.ThrowNoElementsException()
   at System.Linq.Enumerable.Max(IEnumerable`1 source)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitBinary(BinaryExpression binaryExpression)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at System.Dynamic.Utils.ExpressionVisitorUtils.VisitBlockExpressions(ExpressionVisitor visitor, BlockExpression block)
   at System.Linq.Expressions.ExpressionVisitor.VisitBlock(BlockExpression node)
   at System.Linq.Expressions.BlockExpression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at System.Linq.Expressions.Expression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.ShaperProcessingExpressionVisitor.ProcessShaper(Expression shaperExpression, RelationalCommandCache& relationalCommandCache, LambdaExpression& relatedDataLoaders, Int32& collectionId)
   at Microsoft.EntityFrameworkCore.Query.RelationalShapedQueryCompilingExpressionVisitor.VisitShapedQuery(ShapedQueryExpression shapedQueryExpression)
   at Microsoft.EntityFrameworkCore.Query.ShapedQueryCompilingExpressionVisitor.VisitExtension(Expression extensionExpression)
   at System.Linq.Expressions.Expression.Accept(ExpressionVisitor visitor)
   at System.Linq.Expressions.ExpressionVisitor.Visit(Expression node)
   at Microsoft.EntityFrameworkCore.Query.QueryCompilationContext.CreateQueryExecutor[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Storage.Database.CompileQuery[TResult](Expression query, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.CompileQueryCore[TResult](IDatabase database, Expression query, IModel model, Boolean async)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.<>c__DisplayClass9_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Query.Internal.CompiledQueryCache.GetOrAddQuery[TResult](Object cacheKey, Func`1 compiler)
   at Microsoft.EntityFrameworkCore.Query.Internal.QueryCompiler.Execute[TResult](Expression query)
   at Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryProvider.Execute[TResult](Expression expression)
   at Microsoft.EntityFrameworkCore.EntityFrameworkQueryableExtensions.ToQueryString(IQueryable source)
   at Elwis.Orders.Persistence.GroupQueries.GetGroups(AccountId accountId, SalesGroupId salesGroupId, GroupStatus groupStatus, GroupAccountRole groupAccountRole, PermissionLevel permissionLevel, String sortingColumn, SortingDirection sortingDirection, Int32 pageSize, Int32 pageNumber) in C:\Users\micro\source\repos\rtsforder\Elwis.Orders.Persistence\Read\Queries\GroupQueries.cs:line 50

  This exception was originally thrown at this call stack:
    [External Code]
    Elwis.Orders.Persistence.GroupQueries.GetGroups(Elwis.SharedKernel.Domain.AccountId, Elwis.Orders.Domain.SalesGroupId, Elwis.Orders.Domain.GroupStatus, Elwis.Orders.Domain.GroupAccountRole, Elwis.SharedKernel.Domain.PermissionLevel, string, Elwis.SharedKernel.Domain.Enums.SortingDirection, int, int) in GroupQueries.cs

我简化了 sql 代码以定位错误并从连接表返回常量值。 我使用ToQueryString()到 output 生成的 SQL 到控制台。

var query = _dbContext.Set<GetGroupDTO>().FromSqlRaw(@"
    Select  GroupId, SalesGroupName='RTSF', Name, Owner, Status='OPEN', 
    [Start], [End], AccountRole='Owner', Suspended, 
    Created, LastUpdated, ChangedBy, _eTag
    FROM OD.[Group]");

Console.WriteLine(query.ToQueryString());

ToQueryString()不应该运行查询，只是 output 和 SQL。由于上面的测试 SQL 不使用任何参数，它不应该抛出任何错误。 我不明白是什么导致了这个错误？

查询 object 是在此处创建的：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
   base.OnModelCreating(modelBuilder);
   modelBuilder.Entity<GetGroupDTO>().HasNoKey();
}

class 存放查询结果：

public class GetGroupDTO
{
    public Guid GroupId { get; }
    public string SalesGroupName { get; }
    public string Name { get; }
    public Guid Owner { get; }
    public string Status { get; }
    public DateTime Start { get; }
    public DateTime End { get; }
    public string AccountRole { get; }
    private bool Suspended { get; }
    public DateTime Created { get; }
    public DateTime LastUpdated { get; }
    public Guid ChangedBy { get; }
    public ulong _eTag { get; }

    private GetGroupDTO() { }
}

是否需要任何其他代码来回答这个问题？

更新：

我尝试了另一个 SQL 语句，该语句使用了用于写入的组 object。 这次电话接通了。 错误似乎来自查询 object 的声明。

var group = _dbContext.Set<Group>()
  .FromSqlRaw("SELECT * FROM OD.[Group]").ToList();

Answer 1

为您的属性添加set或init 。 EF Core 无法为只读属性生成分配，这就是它失败的原因。

对于这种情况，他们可能必须抛出更多信息异常。