Linq.Dynamic FirstOrDefault() nested in OrderBy

Question

I have the following Linq statement, which works totally fine:

query = query.OrderBy(m => m.MATERIAL_TXT.Where(mt => mt.LANG == "EN").FirstOrDefault().LTEXT);

Now I'm trying to make it dynamic by using the string based syntax from Linq.Dynamic:

query = query.OrderBy("MATERIAL_TXT.Where(LANG==\"EN\").FirstOrDefault().LTEXT");

But it throws the exception :

"No applicable aggregate method 'FirstOrDefault' exists"

It has to bedynamic so that it accepts other names instead of "MATERIAL_TXT".

What am I missing?

Answer 1

According to the documentation:

A subset of the Standard Query Operators is supported for objects that implement IEnumerable. Specifically, the following constructs are permitted, where seq is an IEnumerable instance, predicate is a boolean expression, and selector is an expression of any type:

• seq.Where(predicate)
• seq.Any()
• seq.Any(predicate)
• seq.All(predicate)
• seq.Count()
• seq.Count(predicate)
• seq.Min(selector)
• seq.Max(selector)
• seq.Sum(selector)
• seq.Average(selector)

FirstOrDefault isn't on the list, so it's reasonably safe to assume it isn't supported.

Answer 2

You can't use FirstOrDefault as string like that.

if you want to create dynamic orderBy try this :

Func<IQueryable<YourEntityType>, IOrderedQueryable<YourEntityType>> orderBy;

   orderBy = x => x.OrderBy(m => m.MATERIAL_TXT.Where(mt => mt.LANG == "EN").FirstOrDefault().LTEXT);

Then you can use it like this :

orderBy(query);

for example you can use it in another method :

public List<YourEntityType> YourMethodName(Func<IQueryable<YourEntityType>, IOrderedQueryable<YourEntityType>> orderBy,IQueryable<YourEntityType> query=null)
{
     query=query ?? GetYourEntityTypeList().AsQueryable();
     return orderBy(query).ToList();
}

I Hope it will be useful .