C#LINQ拋出了這個錯誤。我該如何解決？

代碼拋出此例外 - 我該如何解決？

System.InvalidOperationException: LINQ 運算式 'GroupByShaperExpression: KeySelector: (Nullable)d.DiseasesCategoryId, ElementSelector:EntityShaperExpression: EntityType: Diagnosis ValueBufferExpression: ProjectionBindingExpression: EmptyProjectionMember IsNullable: False .GroupBy(p.翻譯。以可翻譯的形式重寫查詢，或通過插入對“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的呼叫，顯式切換到客戶端評估。有關詳細資訊，請參閱https://go.microsoft.com/fwlink/?linkid=2101038。

代碼：

IQueryable<Diagnosis> diagnoses = _context.Diagnosis
    .Include(d => d.Patient)
    .Include(d => d.Prescription);
IQueryable<Diagnosis> diagnosesWithSpecification = diagnoses
    .Where(d => d.Prescription.UpdatedOn.Year == year && 
                d.Prescription.UpdatedOn.Month == month && 
                d.Prescription.HospitalId == hospitalId);

int currentYear = DateTime.Now.Date.Year;
var groupByDiseases = await diagnosesWithSpecification
    .GroupBy(dCat => dCat.DiseasesCategoryId)
    .Select(x => new
    {
       DiseasesCategoryId = x.Key,
       Gender = x.GroupBy(p => p.Patient.Gender).Select(y => new
       {
           Gender = y.Key,
           ZeroToFive = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) >= 0 && (currentYear - p.Patient.DoB.Value.Date.Year) <= 5),
           SixToFifteen = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) >= 6 && (currentYear - p.Patient.DoB.Value.Date.Year) <= 15),
           SixteenToThirty = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) >= 16 && (currentYear - p.Patient.DoB.Value.Date.Year) <= 30),
           ThirtyOneToFourtyFive = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) >= 31 && (currentYear - p.Patient.DoB.Value.Date.Year) <= 45),
           FourtySixToSixty = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) >= 46 && (currentYear - p.Patient.DoB.Value.Date.Year) <= 60),
           SixtyOnePlus = y.Count(p => (currentYear - p.Patient.DoB.Value.Date.Year) > 60),
           Total = y.Count()
       }).ToList(),
       TotalPatient = x.Count()
    }).ToListAsync();

uj5u.com熱心網友回復：

.ToList()在呼叫 none 資料庫函式之前使用。

diagnosesWithSpecification.ToList().GroupBy(dCat => dCat.DiseasesCategoryId)...

uj5u.com熱心網友回復：

您需要在客戶端分組。在此之前需要對回傳的結果集進行簡化。

var data = await _context.Diagnosis
    .Where(d => d.Prescription.UpdatedOn.Year == year && 
                d.Prescription.UpdatedOn.Month == month && 
                d.Prescription.HospitalId == hospitalId)
    .Select(d = new 
    { 
        d.DiseasesCategoryId,
        d.Patient.Gender,
        p.Patient.DoB
     })
     .ToListAsync();

int currentYear = DateTime.Now.Date.Year;

var groupByDiseases = data
    .GroupBy(dCat => dCat.DiseasesCategoryId)
    .Select(x => new
    {
       DiseasesCategoryId = x.Key,
       Gender = x.GroupBy(p => p.Gender).Select(y => new
       {
           Gender = y.Key,
           ZeroToFive = y.Count(p => (currentYear - p.DoB.Value.Date.Year) >= 0 && (currentYear - p.DoB.Value.Date.Year) <= 5),
           SixToFifteen = y.Count(p => (currentYear - p.DoB.Value.Date.Year) >= 6 && (currentYear - p.DoB.Value.Date.Year) <= 15),
           SixteenToThirty = y.Count(p => (currentYear - p.DoB.Value.Date.Year) >= 16 && (currentYear - p.DoB.Value.Date.Year) <= 30),
           ThirtyOneToFourtyFive = y.Count(p => (currentYear - p.DoB.Value.Date.Year) >= 31 && (currentYear - p.DoB.Value.Date.Year) <= 45),
           FourtySixToSixty = y.Count(p => (currentYear - p.DoB.Value.Date.Year) >= 46 && (currentYear - p.DoB.Value.Date.Year) <= 60),
           SixtyOnePlus = y.Count(p => (currentYear - p.DoB.Value.Date.Year) > 60),
           Total = y.Count()
       }).ToList(),
       TotalPatient = x.Count()
    }).ToList();

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