Query Xml from SQL using Entity Framework Database First

Question

I need to use Entity Framework, LINQ to query the XML data from the SQL in my asp.net mvc(C#) application.

I have a column XMLValue with data

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

I need to get all the Customers who have a Rating of 1 from the xml. I have referred to this stackoverflow post and I am not able to achieve it.

I have added the SQL function and added it to my 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

And the following DB function:

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

Below is the linq query which I tried exactly as in the post, but not able to use the function and it throws error.

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

Error:

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

If I user Any(), I have the following error:

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

Error:

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.

Can someone suggest on how to achieve this please?

Answer 1

I think the problem is caused by the return type of your stub function.

Can you check what the return type for your FilterCustomersByRating method is in your DbContext? I don't think it should be XMLTest. It should look similar to the code below:

[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);
}

In this case, the return type of the stub function would be of type FilterCustomersByRating_Result which is class auto-generated when you add the FilterCustomersByRating Table-valued function to your edmx file.

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

With this in mind your stub function should be return IQueryable<FilterCustomersByRating_Result> i.e.

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

you can the use it as shown below:

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

Please note that while this will work it will return all Customers. You might need to modify the FilterCustomersByRating function to accept theCustomerID and rating.

Give it a try.

EDIT

In addition to the above, when defining the MyXmlHelper EdmFunction, make sure that the spelling of the FunctionName and NamespaceName is correct. In my case, the FunctionName is FilterCustomersByRating and NamespaceName is TestingEntities which match the values in the auto-generated DBContext class.

// </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);
    }
}

Answer 2

First error

where clause in your queries needs to evaluate to a bool value.

MyXmlHelper(1).Where(xh=> xh.XMLValue.Contains("1")) will give a record of type System.Linq.IQueryable<XMLTest> and not bool. You need to come up with a expression which will return a bool value.

Second error

Same is applicable to second error - change your where clause to get bool value from the expression.

Answer 3

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', 'int') LIKE '<Rating>'.@Rating.'</Rating>'
GO

Change "=" to "LIKE". Don't know what N(C) is, cross apply, or N.C.value(), but using = instead of LIKE often gives me trouble. Its trying to cross evaluate ints/bools with strings, and for strings like "1" you should use LIKE