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Problem in Linq query compiler

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LINQ (LINQ specific questions)

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Noam Berda asked on 11 Oct 2011, 01:59 AM

Hi,
I have a short code that add dynamically order by query to an existing query.
This code works fine on EF4.1 but doesn't work on Telerik ORM.

Here is the exception
System.NullReferenceException: Object reference not set to an instance of an object. at Telerik.OpenAccess.Query.ExpressionCompiler.PerformDatabaseQueryImpl(Type type, Int32 elementAt, Object[] groupResolutionParamValues, Boolean single, Boolean checkOid) at Telerik.OpenAccess.Query.ExpressionCompiler.PerformDatabaseQuery(Type type, Int32 elementAt, Object[] groupResolutionParamValues, Boolean single, Boolean checkOid)

here is the linq query that been built
{Extent<XXXX.DB.Report>().Where(x => (x.inStatus == Convert(value(XXXXX.Services.Services.ReportService+<>c__DisplayClass2).statusFilter))).OrderBy(Param_0 => Param_0.Address)}

And here is the code that creates it. i think its a problem with Param_0 variable name, but this the default name when i am using the Parameter expression.

public IQueryable<T> ApplyOrder(IQueryable<T> source)
        {
 
            var sortOrder = (_sortOrder == SortOrder.Ascending) ?
                                "OrderBy" : "OrderByDescending";
            
 
            ParameterExpression[] parameters = new ParameterExpression[] {
                Expression.Parameter(typeof(T)) };
 
            //Dig into lambda expression
            Type fieldType = null;
            MemberExpression memberExpression = null;
            Type t = typeof(T);
            string[] tokenFieldName = _orderByField.Split('.');
            
            foreach (var s in tokenFieldName)
            {
                var properties = TypeDescriptor.GetProperties(t);
                var property = properties[s];
                if (property != null)
                {
                    t = fieldType = property.PropertyType;
                    if (memberExpression == null)
                    {
                        memberExpression = Expression.Property(parameters[0], s);
                    }
                    else
                    {
                        memberExpression = Expression.Property(memberExpression, s);
                    }
                }
                else
                {
                    throw new Exception(string.Format("Cannot find field with name '{0}'", _orderByField));
                }
            }
 
            if (memberExpression != null)
            {
                Expression queryExpr = Expression.Call(
                    typeof(Queryable), sortOrder,
                    new Type[] { typeof(T), fieldType },
                    source.Expression, Expression.Quote(Expression.Lambda(memberExpression, parameters)));
                source = source.Provider.CreateQuery<T>(queryExpr);
 
                return source;
            }
            else
            {
                throw new NullReferenceException("No memberExpression was constructed");
            }
            
        }

4 Answers, 1 is accepted

answered on 11 Oct 2011, 05:52 PM

Hi Thomas,
I have tried to reproduce it for you so you can see the problem. It looks related to the way the param name are been translated. when i am writing the same query in linq then i can see the param name some how get translated to var1. but when i am using the sample code i gave you the param name is kept at "Param_0" i have seen it when i am looking on the Expression.DebugView of the query and comparing the linq vs ApplyOrder method.

Here is how to reproduce it. take your context, and get all the objects of specific entity. (I am using my Report object but i think it will work on any one). Then apply the order filter to the query with the field name and call ToList. it should then throw the exception.

Hope you can reproduce it.
Noam

var q = _xxxxeContext.Reports;

q = ApplyOrder(q, "Address");
var g = q.ToList();

use the following method to apply the order by.

       public IQueryable<T> ApplyOrder<T>(IQueryable<T> source, string fieldName)
        {
 
            var sortOrder = "OrderBy";
 
 
            ParameterExpression[] parameters = new ParameterExpression[] {
                Expression.Parameter(typeof(T)) };
 
            //Dig into lambda expression
            Type fieldType = null;
            MemberExpression memberExpression = null;
            Type t = typeof(T);
            string[] tokenFieldName = new string[] { fieldName };
 
            foreach (var s in tokenFieldName)
            {
                var properties = TypeDescriptor.GetProperties(t);
                var property = properties[s];
                if (property != null)
                {
                    t = fieldType = property.PropertyType;
                    if (memberExpression == null)
                    {
                        memberExpression = Expression.Property(parameters[0], s);
                    }
                    else
                    {
                        memberExpression = Expression.Property(memberExpression, s);
                    }
                }
            }
 
            if (memberExpression != null)
            {
                Expression queryExpr = Expression.Call(
                    typeof(Queryable), sortOrder,
                    new Type[] { typeof(T), fieldType },
                    source.Expression, Expression.Quote(Expression.Lambda(memberExpression, parameters)));
                source = source.Provider.CreateQuery<T>(queryExpr);
 
                return source;
            }
            else
            {
                throw new NullReferenceException("No memberExpression was constructed");
            }
 
        }