"InnerText" on XmlNode in LINQ query do not work

Question

When I call a property "InnerText" on XmlNode in LINQ query I am getting a strange error: "An item with the same key has already been added.".

Query looks like:

var partnersXml = from partnerTable in dataContext.SomeTableInDb
                  where partnerTable.XmlType == "partner"
                  select new
                  {
                     partnerId = XmlDocumentWrapper(partnerTable.XmlDocument).SelectSingleNode("//*[name()='partnerId']").InnerText                 
                  };

Explanation:

• partnerTable.XmlDocument is string xml in DB
• XmlDocumentWrapper method returns a XmlDocument for a given xml string

Query works perfectly without "InnerText" (then partnerId contains XmlNode). Is this some kind of bug in LINQ or what? What is a workaround of this problem?

Stack trace:

System.ArgumentException: An item with the same key has already been added. at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource) at System.Collections.Generic.Dictionary2.Insert(TKey key, TValue value, Boolean add) at System.Data.Linq.Mapping.UnmappedType.GetDataMember(MemberInfo mi) at System.Data.Linq.SqlClient.SqlFactory.Member(SqlExpression expr, MemberInfo member) at System.Data.Linq.SqlClient.QueryConverter.VisitMemberAccess(MemberExpression ma) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitExpression(Expression exp) at System.Data.Linq.SqlClient.QueryConverter.VisitNew(NewExpression qn) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.Visit(Expression node) at System.Data.Linq.SqlClient.QueryConverter.VisitSelect(Expression sequence, LambdaExpression selector) at System.Data.Linq.SqlClient.QueryConverter.VisitSequenceOperatorCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitMethodCall(MethodCallExpression mc) at System.Data.Linq.SqlClient.QueryConverter.VisitInner(Expression node) at System.Data.Linq.SqlClient.QueryConverter.ConvertOuter(Expression node) at System.Data.Linq.SqlClient.SqlProvider.BuildQuery(Expression query, SqlNodeAnnotations annotations) at System.Data.Linq.SqlClient.SqlProvider.System.Data.Linq.Provider.IProvider.Execute(Expression query) at System.Data.Linq.DataQuery1.System.Collections.Generic.IEnumerable.GetEnumerator()

Answer 1

It looks like LINQ to SQL is trying to do some mapping whereas you want it to be done at the .NET side. (I assume - if you want the database to do the XPath, I have no idea I'm afraid.) Try this:

var partnersXml = dataContext.SomeTableInDb
     .Where(x => x.XmlType == "partner")
     .AsEnumerable() // This forces the rest of the query to be done in the CLR
     .Select(x => new {
          partnerId = XmlDocumentWrapper(x.XmlDocument)
                           .SelectSingleNode("//*[name()='partnerId']")
                           .InnerText
     });