IEnumerable在LINQ查询中列出 [英] IEnumerable to list inside linq query

问题描述

我正在尝试运行此查询，在这里我尝试获取类别以及那里的子类别

I am trying to run this query, where I try to fetch categories and there sub categories

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();

当前字段ContinuumCategory.ContinuumSubCategories的类型为List，因此此查询给我一个编译时错误，它无法将IEnumerable转换为列表，当然不能.

Currently the field ContinuumCategory.ContinuumSubCategories is of type List so this query gives me a compile time error that it cannot convert IEnumerable to list, ofcourse it cannot.

由于linq无法识别ToList方法，因此我什至无法在查询中使用该方法.

And as linq does not recognize ToList method so I cannot even use that inside my query.

我可以通过将ContinuumCategory.ContinuumSubCategories的类型更改为IEnumerable来解决我的问题，但是我已经在许多使用List.Add方法的地方使用了此字段，因此我将不得不将所有Add方法替换为，所以这可能很乏味.

I can solve my problem by changing the type of ContinuumCategory.ContinuumSubCategories to IEnumerable but I have already used this field in many places where it uses List.Add method so I will have to replace all the Add methods to IEnumerable.Concat, so this can be tedious.

是否有任何解决方法可直接从linq查询中直接获取连续体子类别列表?

Is there any workaround to directly get the list of continuum sub categories from linq query only?

当我使用此查询时(用于ContinuumSubCategories的查询中使用了ToList()方法)

when I use this query(used ToList() method inside query for ContinuumSubCategories)

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();

我收到此异常

 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.

推荐答案

不要在内部查询(用于ContinuumSubCategories的查询)上调用ToList()

Don't call ToList() on the inner query (the one for ContinuumSubCategories)

使用ToList()将查询分为两部分:

Split your query into two parts with ToList() in-between:

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();

行得通吗?

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