试图串联LINQ中的列 [英] Trying to concatenate columns in LINQ

问题描述

我正在尝试将2列连接成1列用于结果集.

I'm trying to concatenate 2 columns into 1 column for my resultset.

var gridInfo = from leader in db.SchoolLdrAdminAccesses
               join emp in db.Employees
               on leader.ID equals emp.ID
               select new List<string> { leader.ID, string.Format("{0}{1}", emp.FirstName, emp.LastName) };

我遇到此错误:

LINQ to Entities无法识别方法'System.String Format(System.String，System.Object，System.Object)'方法，以及此方法 方法不能转换为商店表达式.

LINQ to Entities does not recognize the method 'System.String Format(System.String, System.Object, System.Object)' method, and this method cannot be translated into a store expression.

我做错了什么?

我必须保留这个:

select new List<string> {...}

当我这样做时，我需要在List结构中使用它.

As I am then doing this and I need it in the List structure.

        return Json(new
        {
            sEcho = param.sEcho,
            iTotalRecords = gridInfo.Count(),
            iTotalDisplayRecords = gridInfo.Count(),
            aaData = gridInfo.ToArray()
        },
        JsonRequestBehavior.AllowGet);

推荐答案

使用+运算符在EF中连接两个字符串:

Use the + operator to concat two strings in EF:

select new List<string> { leader.ID, emp.FirstName + emp.LastName };

与string.Format不同，查询提供程序知道如何将+运算符转换为SQL.

Unlike string.Format, the query provider knows how to translate the +operator into SQL.

为此，请执行相同的操作以连接到您拥有的任何其他C#代码中的字符串.使用string.Format仅连接两个字符串是不必要的复杂操作，从而使读者感到困惑.

And for that matter, do the same thing to concat to strings in any other C# code that you have. Using string.Format to just concat two strings is needlessly complex, thus confusing readers.

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