InvalidQueryExpressionException – the query expression is not supported

The best way to retrieve results from sharepoint list in terms of performance using client object model is to use ‘include’  with lambda expression.

using (var context = newClientContext(http://server/site/sitecollection))

{

 List currentList = context.Site.RootWeb.Lists.GetByTitle(“MyList”);

 CamlQuery camlQuery = newCamlQuery();

camlQuery.ViewXml =“[YourViewXmlhere]”;

 ListItemCollection collListItem = currentList.GetItems(camlQuery);

context.Load(collListItem, items => items.Include(item => item[“ID”], item => item[“SomeField1”], item => item[“SomeField2”]));

context.ExecuteQuery();

 foreach (ListItem item in collListItem)

{

       //Play with the listitem here

 }

}

 What if I had to generate the lambda expression for the include method at runtime. Every expression I created gave me an error saying ‘the query expression is not supported’. Actually, ClientContext.Load() method doesn’t support lambda expressions created at runtime. Due to this limitation, you’ll get ‘InvalidQueryExpressionException’ . Alternative is to use, ClientContext.LoadQuery().

Code snippet –

using(var context = newClientContext(http://server/site/sitecollection))

{

 List currentList = context.Site.RootWeb.Lists.GetByTitle(“MyList”);

 CamlQuery camlQuery = newCamlQuery();

camlQuery.ViewXml =“YourViewXmlhere”;

 ListItemCollection collListItem = currentList.GetItems(camlQuery);

 List<string> viewFields = newList<string>();

viewFields.Add(“ID”);

viewFields.Add(“SomeField1”);

viewFields.Add(“SomeField2”);

 Expression<Func<ListItem, object>>[] listItemExpressions = CreateListItemLoadExpressions(viewFields);

 IEnumerable<ListItem> resultData = context.LoadQuery(collListItem.Include(listItemExpressions));

context.ExecuteQuery();

 foreach (ListItem item in resultData)

{

 //Play with the listitem here

 }

}

private static Expression<Func<ListItem, object>>[] CreateListItemLoadExpressions(List<string> viewFields)

{

 List<Expression<Func<ListItem, object>>> expressions = new List<Expression<Func<ListItem, object>>>();

 foreach (string viewFieldEntry in viewFields)

{

 string fieldInternalName = viewFieldEntry;

 Expression<Func<ListItem, object>> retrieveFieldDataExpression = listItem => listItem[fieldInternalName];

 expressions.Add(retrieveFieldDataExpression);

 }

 return expressions.ToArray();

}