C# .NET MVC在计数（）时返回错误

我有一个问题：

foreach (var item in outcomeAreas)
{
    var outcomeAreasCohorts = db.Cohorts
        .Join(db.OutcomeArea, c => c.ID, oa => oa.CohortID, (c, oa) => new { c = c, oa = oa })
        .Where(oa => oa.oa.OutcomeType.Contains(item.SubCategory.ToString()))
        .Select(c => new { c.c.cohortID }).Distinct().ToList().Count();

    allFilters.Add(new GetFilters { Category = item.Category, Identifier = item.Identifier, SubCategory = item.SubCategory, SubCategoryIdentifier = item.SubCategory.ToString().Replace(" ", "-"), TopLevel = "Key Cohort Outcomes", TotalNum = outcomeAreasCohorts.ToString() });

}

然而，这给我带来了一个错误

Values of type 'collection[Edm.String(Nullable=True,DefaultValue=,MaxLength=,Unicode=,FixedLength=)]' can not be converted to string.

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我尝试搜索，但没有找到此错误。想法？

尝试删除该实体并将其添加回edmx。通常有效。你是说把它从课堂上移除吗？明白了。谢谢