c# - Linq.Dynamic FirstOrDefault() 嵌套在 OrderBy 中

Question

我有以下 Linq 语句，它工作得很好:

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

现在我尝试使用 Linq.Dynamic 中基于字符串的语法使其动态化:

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

但它抛出异常:

"No applicable aggregate method 'FirstOrDefault' exists"

它必须是动态的，以便它接受其他名称而不是“MATERIAL_TXT”。

我错过了什么？

Answer 1

根据文档:

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 不在列表中，因此可以合理地假设它不受支持。