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c# - 尽管使用了 ToLists，但无法翻译 LINQ 表达式

问题描述

我有以下代码，我首先创建一个列表对象assessmentItems，然后在 LINQ 中使用它来获取CurrentScore.

List<AssessmentItem> assessmentItems =
    _context.AssessmentItems
            .Include(ai => ai.Assessment).ThenInclude(assess => assess.Evaluator)
            .Where(ai => ai.IsActive &&
                         ai.Assessment.PeerReviewAssignmentId == peerReviewAssignmentId &&
                         ai.Assessment.RubricId == rubricId).ToList();


List<RubricDTO> resultToReturn = _context.Rubrics
                .Include(r => r.RubricItemCategories)
                .Where(r => r.Id == rubricId)
                .Select(r => new RubricDTO
                {
                    Ranking = r.Ranking,                       
                    Description = r.Description,
                    RubricItemCategories = r.RubricItemCategories.Select(ric => new RubricItemCategoryDTO
                    {
                        Id = ric.Id,
                        Description = ric.Description,
                        RubricItems = ric.RubricItems.Select(ri => new RubricItemDTO
                        {
                            Id = ri.Id,
                            Title = ri.Title,                     
                          
                            CurrentScore = assessmentItems.Count > 0 ? assessmentItems
                                                  .Where(aitem2 => aitem2.RubricItemId == ri.Id && aitem2.Assessment.EvaluatorId == userId)
                                                  //.Take(1)
                                                  .Select(s => s.CurrentScore)
                                                  .FirstOrDefault() : 0,

                        })
                    }).OrderBy(ric => ric.Order).ToList()
                }).ToList();

但是，我收到以下错误：

System.InvalidOperationException：无法翻译 LINQ 表达式“aitem2”。以可翻译的形式重写查询，或通过插入对“AsEnumerable”、“AsAsyncEnumerable”、“ToList”或“ToListAsync”的调用显式切换到客户端评估。有关详细信息，请参阅https://go.microsoft.com/fwlink/?linkid=2101038。

任何想法为什么会发生这种情况？

标签： c#entity-frameworklinq

解决方案

让我帮助您简化查询。不需要包含，因为您有自定义投影。如果您添加ToList子查询元素 - 它将无法翻译。如果您需要可翻译的查询 - 使用 IQueryable。

var assessmentItems = _context.AssessmentItems
    .Where(ai => ai.IsActive &&
                    ai.Assessment.PeerReviewAssignmentId == peerReviewAssignmentId &&
                    ai.Assessment.RubricId == rubricId);

var resultToReturn = _context.Rubrics
    .Where(r => r.Id == rubricId)
    .Select(r => new RubricDTO
    {
        Ranking = r.Ranking,                       
        Description = r.Description,
        RubricItemCategories = r.RubricItemCategories.Select(ric => new RubricItemCategoryDTO
        {
            Id = ric.Id,
            Description = ric.Description,
            RubricItems = ric.RubricItems.Select(ri => new RubricItemDTO
            {
                Id = ri.Id,
                Title = ri.Title,                     
                
                CurrentScore = assessmentItems
                                    .Where(aitem2 => aitem2.RubricItemId == ri.Id && aitem2.Assessment.EvaluatorId == userId)
                                    .Select(s => s.CurrentScore)
                                    .FirstOrDefault(),

            })
        }).OrderBy(ric => ric.Order).ToList()
    }).ToList();

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