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我正在尝试运行此查询，我尝试在其中获取类别和子类别

studentCont.ContinuumCategories = db.continuumcategorymasters
    .Where(x => x.AssessmentId == assessmentId && x.ContinuumCategory != "other")
    .Select(x => new ContinuumCategory()
    {
        AssessmentId = x.AssessmentId,
        ContinuumCategoryId = x.ContinuumCategoryId,
        NativeAppid = x.NativeAppCategoryId,
        score = 0,
        ContinuumCategoryName = x.ContinuumCategory,
        ContinuumSubCategories = x.continuumsubcategorymasters
            .Select(csc => new ContinuumSubCategory
            {
                ContinuumSubCategoryId = csc.ContinuumSubCategotyId,
                ContinuumSubCategoryName = csc.ContinuumSubCategotyName,
                NativeAppsubid = csc.NativAppSubCategotyId
            })
    })
    .ToList();

目前该字段ContinuumCategory.ContinuumSubCategories是类型List，所以这个查询给了我一个编译时错误，它不能转换IEnumerable为列表，当然不能。

由于 linq 无法识别ToList方法，因此我什至无法在查询中使用它。

ContinuumCategory.ContinuumSubCategories我可以通过更改 to 的类型来解决我的问题，IEnumerable但是我已经在许多使用方法的地方使用了这个字段，List.Add所以我必须将所有 Add 方法替换为IEnumerable.Concat，所以这可能很乏味。

是否有任何解决方法可以仅从 linq 查询中直接获取连续子类别列表？

编辑：

当我使用此查询时（ToList()ContinuumSubCategories 查询中使用的方法）

studentCont.ContinuumCategories = db.continuumcategorymasters
    .Where(x => x.AssessmentId == assessmentId && x.ContinuumCategory != "other")
    .Select(x => new ContinuumCategory()
    {
        AssessmentId = x.AssessmentId,
        ContinuumCategoryId = x.ContinuumCategoryId,
        NativeAppid = x.NativeAppCategoryId,
        score = 0,
        ContinuumCategoryName = x.ContinuumCategory,
        ContinuumSubCategories = x.continuumsubcategorymasters
            .Select(csc => new ContinuumSubCategory
            {
                ContinuumSubCategoryId = csc.ContinuumSubCategotyId,
                ContinuumSubCategoryName = csc.ContinuumSubCategotyName,
                NativeAppsubid = csc.NativAppSubCategotyId
            }).ToList()
    })
    .ToList();

我得到了这个例外

 LINQ to Entities does not recognize the method 'System.Collections.Generic.List1[BusinessObjects.ContinuumSubCategory] ToList[ContinuumSubCategory]
    (System.Collections.Generic.IEnumerable1[BusinessObjects.ContinuumSubCategory])' method, and this method cannot be translated into a store expression.
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1 回答 1

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不要调用ToList()内部查询（ for ContinuumSubCategories）

将您的查询分成两部分，ToList()中间有：

studentCont.ContinuumCategories = db.continuumcategorymasters
    .Where(x => x.AssessmentId == assessmentId && x.ContinuumCategory != "other")
    .ToList()  // Fetch all the data from the db
    .Select(x => new ContinuumCategory
    {
        AssessmentId = x.AssessmentId,
        ContinuumCategoryId = x.ContinuumCategoryId,
        NativeAppid = x.NativeAppCategoryId,
        score = 0,
        ContinuumCategoryName = x.ContinuumCategory,
        ContinuumSubCategories = (x.continuumsubcategorymasters
            .Select(csc => new ContinuumSubCategory
            {
                ContinuumSubCategoryId = csc.ContinuumSubCategotyId,
                ContinuumSubCategoryName = csc.ContinuumSubCategotyName,
                NativeAppsubid = csc.NativAppSubCategotyId
            })).ToList()
    }).ToList();

它有效吗？

于 2013-01-29T08:56:22.460 回答