实体框架转换错误

Question

以下工作完美:

IQueryable<Property> PropertyQuery = PropertyDAO.SearchWithAdditionalParameters(/* elided */);
IQueryable<long> propertyIdQuery = PropertyQuery.Select(p => p.PropertyId);

var relevantFMVs = PropertyDAO.db.FMVHistories.Where(f => propertyIdQuery.Contains(f.PropertyId)).ToList();

但是以下情况爆发了:

IQueryable<Property> PropertyQuery = PropertyDAO.SearchWithAdditionalParameters(/* elided */);

var relevantFMVs = PropertyDAO.db.FMVHistories.Where(f => PropertyQuery.Select(p => p.PropertyId).Contains(f.PropertyId)).ToList();

(请注意,我没有单独创建propertyIdQuery,而只是将变量本身替换为查询本身)

例外是

无法转换类型'System.Linq.IQueryable 1' to type 'System.Linq.IQueryable1'.LINQ to Entities仅支持转换实体数据模型基元类型.

有人可以了解EF(4)在封面下做什么只做第一次查询工作,即使它们表面上是等效的吗？

我知道IQueryable<T>,表达树在幕后做了很多事情,但是如何将中间步骤保存到局部变量会影响结果呢？

编辑

根据请求,这是被调用的完整方法,以及该方法调用的方法:

    public IQueryable<Property> BasicSearchFromConstraints(PropertyInvoiceConstraints constraints) {
        return ExecuteSearchFromConstraints((dynamic)constraints.PropertyInst, constraints.CompanyNumber, constraints.TaxSubType, constraints.PhaseID, constraints.State, constraints.County, constraints.City, constraints.Jurisdiction);
    }

    private IQueryable<T> ExecuteSearchFromConstraints<T>(T property, int CompanyNumber, byte SubType, byte PhaseID, string State, string County, string City, string Jurisdiction) where T : Property {
        IQueryable<T> result = base.db.Properties.OfType<T>();

        if (SubType > 0)
            result = result.Where(p => p.TaxSubTypeId == SubType);
        if (CompanyNumber > 0)
            result = result.Where(p => p.CompanyNum == CompanyNumber);
        if (!String.IsNullOrEmpty(State))
            result = result.Where(p => p.State == State);
        if (!String.IsNullOrEmpty(County))
            result = result.Where(p => p.County == County);
        if (!String.IsNullOrEmpty(City))
            result = result.Where(p => p.City == City);
        if (!String.IsNullOrEmpty(Jurisdiction))
            result = result.Where(p => p.Jurisdiction == Jurisdiction);

        if (PhaseID > 0)
            result = result.Where(p => p.PhaseId == PhaseID);

        return result;
    }

    public virtual IQueryable<Property> SearchWithAdditionalParameters(DataLayer.DAO.PropertyInvoiceConstraints constraints, string propertyNumber = "", string altDesc = "", string countyAcctNumber = "", string City = "", string Jurisdiction = "", string secondaryStateID = "", string LegalDesc = "", string status = "", int? TaxYear = null) {
        IQueryable<Property> result = BasicSearchFromConstraints(constraints);

        if (!String.IsNullOrEmpty(status))
            result = result.Where(p => p.Status == status);

        if (!String.IsNullOrEmpty(propertyNumber))
            result = result.Where(p => p.PropertyNum.Contains(propertyNumber));

        if (!String.IsNullOrEmpty(altDesc))
            result = result.Where(p => p.AltDescription.Contains(altDesc));

        if (!String.IsNullOrEmpty(countyAcctNumber))
            result = result.Where(p => p.CountyAccountNum.Contains(countyAcctNumber));

        if (!String.IsNullOrEmpty(City))
            result = result.Where(p => p.City.Contains(City));

        if (!String.IsNullOrEmpty(Jurisdiction))
            result = result.Where(p => p.Jurisdiction.Contains(Jurisdiction));

        if (TaxYear.HasValue)
            result = result.Where(p => p.FMVHistories.Any(f => f.TaxYear == TaxYear));

        if (constraints.FMVPhaseID > 0)
            result = result.Where(p => p.FMVHistories.Any(f => f.PhaseId == constraints.FMVPhaseID));

        if (!String.IsNullOrEmpty(secondaryStateID))
            if (constraints.PropertyInst is WellDetail)
                result = result.OfType<WellDetail>().Where(w => w.SecondaryStateId == secondaryStateID);
            else
                throw new ApplicationException("Invalid use -> Secondary State ID can only be set when searching for Well property types");

        if (!String.IsNullOrEmpty(LegalDesc))
            if (constraints.PropertyInst is RealEstateDetail)
                result = result.OfType<RealEstateDetail>().Where(r => r.LegalDescr.Contains(LegalDesc));
            else if (constraints.PropertyInst is RealEstateServicingDetail)
                result = result.OfType<RealEstateServicingDetail>().Where(r => r.LegalDescr.Contains(LegalDesc));
            else throw new ApplicationException("Invalid use -> Legal Description can only be set when searching for either real estate or real estate servicing property types");

        return result;
    }

编辑

我真的希望Akash的答案是正确的,但如果是的话,我希望这里的中间查询能够爆炸,但实际上这三个工作都很好.

我开始怀疑我在类型上的继承结构Property(来自原始示例)可能与此有关.

        DummyBookModelEntities db = new DummyBookModelEntities();

        IQueryable<int> BookIds = db.Books.Where(b => b.id < 4).Select(b => b.id);
        IQueryable<Book> BooksFromIdQuery = db.Books.Where(b => b.id < 4);

        try {
            var l1 = db.Books.Where(b => BookIds.Contains(b.id)).ToList();
            Console.WriteLine("ID Query With ID Local Var Worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("ID Query Failed:");
            Console.WriteLine(E.ToString());
            Console.WriteLine();
        }

        try {
            var l1 = db.Books.Where(b => BooksFromIdQuery.Select(b_inner => b_inner.id).Contains(b.id)).ToList();
            Console.WriteLine("ID Query With Whole Book Local Var Worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("ID Query With Whole Book Local Var Failed:");
            Console.WriteLine(E.ToString());
            Console.WriteLine();
        }

        try {
            var l1 = db.Books.Where(b => BooksFromIdQuery.Contains(b)).ToList();
            Console.WriteLine("Whole Book sub query without select worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("Whole Book sub query without select:");
            Console.WriteLine(E.ToString());
            Console.WriteLine();
        }

编辑

我添加了一些继承,现在底部的两个查询失败了.看起来你OfType()在查询中有任何时候,EF根本不想解析查询中的整个查询; 你必须将你的子步骤分解为局部变量.

我今晚会给阿卡什奖励,除非有人有别的东西要补充.

        DummyBookModelEntities db = new DummyBookModelEntities();

        IQueryable<int> BookIds = db.Books.OfType<SciFiBook>().Where(b => b.id < 4).Select(b => b.id);
        IQueryable<Book> BooksFromIdQuery = db.Books.OfType<SciFiBook>().Where(b => b.id < 4);

        try {
            var l1 = db.Books.Where(b => BookIds.Contains(b.id)).ToList();
            Console.WriteLine("ID Query With ID Local Var Worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("ID Query Failed:");
            Console.WriteLine(E.Message);
            Console.WriteLine();
        }

        try {
            var l1 = db.Books.Where(b => BooksFromIdQuery.Select(b_inner => b_inner.id).Contains(b.id)).ToList();
            Console.WriteLine("ID Query With Whole Book Local Var Worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("ID Query With Whole Book Local Var Failed:");
            Console.WriteLine(E.Message);
            Console.WriteLine();
        }

        try {
            var l1 = db.Books.Where(b => BooksFromIdQuery.Contains(b)).ToList();
            Console.WriteLine("Whole Book sub query without select worked: count = {0}", l1.Count);
        } catch (Exception E) {
            Console.WriteLine("Whole Book sub query without select:");
            Console.WriteLine(E.Message);
            Console.WriteLine();
        }

        Console.WriteLine();  

Answer 1

f => PropertyQuery.Select(p => p.PropertyId).Contains(f.PropertyId)

上面是一个 linq 表达式，f=> 之后的所有内容都是表达式树。Composite Linq 只能基于表达式扩展查询，而不能基于委托扩展查询。

您的两个语句集在逻辑上都是正确的，但从编译器的角度来看它们是不同的。如果您注意到扩展（where on where 或 select）仅适用于相同类型的模板参数。在其他地方，您的 int 的 IQueryable 将无法工作，因为您的 linq 需要 T 的 IQueryable 。

其次，当您对 T 执行 Select 并返回 T 的 IQueryable 时，运行时无法知道之前的 T 是什么类型。

简而言之，将中间步骤保存为局部变量会破坏表达式树。我建议您查看 Reflector 以查看实际生成的源代码。

您的整个 lambda 表达式实际上是使用表达式节点构建的，并且构建了整个树并将其返回给Where 方法。在第一个示例中，表达式树的其他地方有所不同，它涉及表达式中其他内容的执行。