使用Entity Framework Database First从SQL查询Xml

Question

我需要使用Entity Framework,LINQ在我的asp.net mvc(C#)应用程序中查询SQL中的XML数据.

我有一个XMLValue包含数据的列

<MetaData>
     <Reviews>1</Reviews>
     <Rating>1</Rating>
</MetaData>

我需要从xml中获得所有Customers拥有Rating1的人.我已经提到了这个stackoverflow帖子,我无法实现它.

我添加了SQL函数并将其添加到我的edmx:

CREATE FUNCTION [dbo].[FilterCustomersByRating] 
    (@Rating int) 
RETURNS TABLE
AS 
RETURN
    SELECT XMLTest.*
    FROM XMLTest
    CROSS APPLY XMLValue.nodes('//MetaData') N(C)
    where N.C.value('Rating[1]', 'int')=@Rating
GO

以及DB功能:

[DbFunction("XMLDBModel.Store", "FilterCustomersByRating")]
public static IQueryable<XMLTest> MyXmlHelper(int rating)
{
            throw new NotImplementedException("You can only call this function in a LINQ query");
}

下面是我在帖子中完全尝试的linq查询,但是无法使用该函数并且它会抛出错误.

 var _dbCustomers = (from x in _context.XMLTests
                     where MyXmlHelper(1).Where(xh=> xh.XMLValue.Contains("1"))
                     select x);

错误:

Cannot implicitly convert type 'System.Linq.IQueryable<XMLTest>' to 'bool

如果我用户Any(),我有以下错误:

 var _dbCustomers = (from x in _context.XMLTests
                          where MyXmlHelper(1).Any(xh => xh.XMLValue.Contains("1"))
                          select x);

错误:

The specified method 'System.Linq.IQueryable`1[XMLTest] MyXmlHelper(Int32)' on the type 'CustomerRepository' cannot be translated into a LINQ to Entities store expression because its return type does not match the return type of the function specified by its DbFunction attribute.

有人可以建议如何实现这一目标吗？

Answer 1

我认为问题是由存根函数的返回类型引起的.

你能检查一下FilterCustomersByRatingDbContext中你的方法的返回类型吗？我认为不应该这样XMLTest.它应该类似于下面的代码:

[EdmFunction("TestingDbEntities", "FilterCustomersByRating")]
public virtual IQueryable<FilterCustomersByRating_Result> FilterCustomersByRating(Nullable<int> rating)
{
    var ratingParameter = rating.HasValue ?
        new ObjectParameter("Rating", rating) :
        new ObjectParameter("Rating", typeof(int));

    return ((IObjectContextAdapter)this)
    .ObjectContext
    .CreateQuery<FilterCustomersByRating_Result>("[TestingEntities]
        .[FilterCustomersByRating](@Rating)", ratingParameter);
}

在这种情况下,存根函数的返回类型将是类型FilterCustomersByRating_Result,当您将FilterCustomersByRating表值函数添加到edmx文件时,该类是自动生成的类.

CREATE FUNCTION [dbo].[FilterCustomersByRating] 
    (@Rating int) 
RETURNS TABLE
AS 
RETURN
    SELECT XMLTest.*
    FROM XMLTest
    CROSS APPLY XMLValue.nodes('//MetaData') N(C)
    where N.C.value('Rating[1]', 'int')=@Rating
GO

考虑到这一点,你的存根函数应该返回IQueryable<FilterCustomersByRating_Result> ie

[EdmFunction("TestingDbEntities", "FilterCustomersByRating")]
public static IQueryable<FilterCustomersByRating_Result> MyXmlHelper(int rating)
{ 
    throw new NotImplementedException("You can only call this function in a LINQ query");
}

你可以使用它,如下所示:

var dbCustomers = (from x in _context.XMLTests
                   where MyXmlHelper(1).Any(xh => xh.XMLValue.Contains("1"))
                   select x);

请注意,虽然这将工作,它将返回所有Customers.您可能需要修改FilterCustomersByRating函数以接受CustomerID和rating.

试试看.

编辑

除了上面的,定义时MyXmlHelper EdmFunction,确保的拼写FunctionName和NamespaceName是正确的.在我的例子中,FunctionNameis FilterCustomersByRating和NamespaceName是TestingEntities匹配自动生成的DBContext类中的值.

// </auto-generated code>
public partial class TestingEntities : DbContext
{
    public TestingEntities()
        : base("name=TestingEntities")
    {
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
        throw new UnintentionalCodeFirstException();
    }

    public DbSet<XMLTest> XMLTests { get; set; }

    [EdmFunction("TestingEntities", "FilterCustomersByRating")]
    public virtual IQueryable<FilterCustomersByRating_Result> FilterCustomersByRating(Nullable<int> rating)
    {
        var ratingParameter = rating.HasValue ?
            new ObjectParameter("Rating", rating) :
            new ObjectParameter("Rating", typeof(int));

        return ((IObjectContextAdapter)this)
        .ObjectContext
        .CreateQuery<FilterCustomersByRating_Result>("[TestingEntities]
            .[FilterCustomersByRating](@Rating)", ratingParameter);
    }
}