C# – Problem using string.IsnullorEmpty in linq query

clinq

I have a linq query in which i want to include those record which are not null or empty in database field but when i use string.isNullorEmpty it gives me error. How can i achieve this task my query is

from post in PostIdPostMeta1
join pstmt in postrepository.GetAllPostMetas() on post.int_PostId equals pstmt.int_PostId
where string.IsNullOrEmpty(pstmt.vcr_MetaValue) == false
select post

If i change string.IsNullOrEmpty(pstmt.vcr_MetaValue) == false to pstmt.vcr_MetaValue != string.Empty it give me SQL Server does not handle comparison of NText, Text, Xml, or Image data types error

Best Answer

Well, the error message seems reasonably clear - I suspect that if you want to be able to do this, you'll need to use an nvarchar field instead of text / ntext.

EDIT: It's not just the database field that needs to be the right type; it's also the type that LINQ to SQL thinks it is. You need to keep your DBML in sync with your actual database schema.

Related Solutions

C# – LINQ query on a DataTable

You can't query against the DataTable's Rows collection, since DataRowCollection doesn't implement IEnumerable<T>. You need to use the AsEnumerable() extension for DataTable. Like so:

var results = from myRow in myDataTable.AsEnumerable()
where myRow.Field<int>("RowNo") == 1
select myRow;

And as @Keith says, you'll need to add a reference to System.Data.DataSetExtensions

AsEnumerable() returns IEnumerable<DataRow>. If you need to convert IEnumerable<DataRow> to a DataTable, use the CopyToDataTable() extension.

Below is query with Lambda Expression,

var result = myDataTable
    .AsEnumerable()
    .Where(myRow => myRow.Field<int>("RowNo") == 1);

C# – Should ‘using’ directives be inside or outside the namespace

There is actually a (subtle) difference between the two. Imagine you have the following code in File1.cs:

// File1.cs
using System;
namespace Outer.Inner
{
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now imagine that someone adds another file (File2.cs) to the project that looks like this:

// File2.cs
namespace Outer
{
    class Math
    {
    }
}

The compiler searches Outer before looking at those using directives outside the namespace, so it finds Outer.Math instead of System.Math. Unfortunately (or perhaps fortunately?), Outer.Math has no PI member, so File1 is now broken.

This changes if you put the using inside your namespace declaration, as follows:

// File1b.cs
namespace Outer.Inner
{
    using System;
    class Foo
    {
        static void Bar()
        {
            double d = Math.PI;
        }
    }
}

Now the compiler searches System before searching Outer, finds System.Math, and all is well.

Some would argue that Math might be a bad name for a user-defined class, since there's already one in System; the point here is just that there is a difference, and it affects the maintainability of your code.

It's also interesting to note what happens if Foo is in namespace Outer, rather than Outer.Inner. In that case, adding Outer.Math in File2 breaks File1 regardless of where the using goes. This implies that the compiler searches the innermost enclosing namespace before it looks at any using directive.

Best Answer

Related Solutions

C# – LINQ query on a DataTable

C# – Should ‘using’ directives be inside or outside the namespace

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