這是我第一次使用 EF Core 的查詢模式。因為我的帶有引數的大型查詢也拋出了例外“序列不包含元素”。
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
我簡化了 sql 代碼以本地化錯誤并從連接表中回傳常量值。我曾經ToQueryString()將生成的 SQL 輸出到控制臺。
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()不應該運行查詢，只輸出 SQL。由于上面的測驗 SQL 沒有使用任何引數，它不應該拋出任何錯誤。我不明白是什么導致了這個錯誤？
查詢物件在這里創建：
protected override void OnModelCreating(ModelBuilder modelBuilder)
{
base.OnModelCreating(modelBuilder);
modelBuilder.Entity<GetGroupDTO>().HasNoKey();
}
保存查詢結果的類：
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碼來回答這個問題？
更新：
我嘗試了另一個使用用于寫入的 Group 物件的 SQL 陳述句。這次電話打通了。似乎錯誤來自查詢物件的宣告。
var group = _dbContext.Set<Group>()
.FromSqlRaw("SELECT * FROM OD.[Group]").ToList();
uj5u.com熱心網友回復：
添加set或init為您的屬性。EF Core 無法為只讀屬性生成分配，這就是它失敗的原因。
可能他們必須為這種情況拋出更多資訊例外。
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