聚合一对多的一方并绑定到Entity Framework中的gridview [英] Aggregating one side of a many-to-many and bind to gridview in Entity Framework

问题描述

CompanyNotice （MM）我的数据库/实体框架模型中有一个多对多的结构） CompanyNoticesLocations （MM）位置

  if（！IsPostBack）
 {
使用（var context = new ALEntities（））
 {
 var query = from c in context.CompanyNotices.Include（Locations）
选择新
 {
 c.CompanyNoticeHeading，
 c.CompanyNoticeText，
 c.IsHR，
 locations =（from c in c.Locations select l.LocationName）.Aggregate（（current，next）=> string .Format（{0}，{1}，当前，下一个））
 
}; 
 ASPxGridView1.DataSource = query; 
 ASPxGridView1.DataBind（）; 
} 
} 
  

当我尝试上述代码时，我收到以下错误：

LINQ to Entities不会识别方法'System.String
Aggregate [String]（System.Collections.Generic。 IEnumerable 1 [System.String]，
System.Func 3 [System.String，System.String，System.String]）'方法和
这个方法不能被翻译成一个存储表达式。

当我尝试：

$（$）
{
使用（var context = new ALEntities（））
{
var query = from c在上下文中.CompanyNotices.Include（Locations）
选择新
{
c.CompanyNoticeHeading，
c.CompanyNoti ceText，
c.IsHR，
locations =（从c.Locations中的l选择l.LocationName）

};
ASPxGridView1.DataSource = query;
ASPxGridView1.DataBind（）;
}
}

gridview中位置列中的数据显示为：

System.Collections.Generic.List`1 [System.String]

有没有人知道如何聚合一个CompanyNotice出现的LocationName？

提前感谢。

解决方案

你可以这样...

  （var context = new ALEntities（））
 {
 var query = from c in context.CompanyNotices.Include（Locations）
选择新
 {
 c .CompanyNoticeHeading，
 c.CompanyNoticeText，
 c.IsHR，
 loc ations =（from c in c.Locations select l.LocationName）
 
}; 
 var listed = query.ToList（）; 
 var commaListed = listed.Select（a => new {a.CompanyNoticeHeading，a.CompanyNoticeText，
 commaLines = a.locations.Aggregate（（s1，s2）=> s1 +， + s2）}）; 
  

然后将逗号列表绑定到您的datagrid

I have a many-to-many structure in place in my database / Entity Framework model.

CompanyNotice (M-M) CompanyNoticesLocations (M-M) Locations

I am trying to aggregate the Locations for one CompanyNotice and return a comma-separated LocationName for the Locations. I have tried using the following code to aggregate the LocationName:

if (!IsPostBack)
            {
                using (var context = new ALEntities())
                {
                    var query = from c in context.CompanyNotices.Include("Locations")
                                select new 
                                { 
                                    c.CompanyNoticeHeading, 
                                    c.CompanyNoticeText,
                                    c.IsHR,
                                    locations = (from l in c.Locations select l.LocationName).Aggregate((current, next) => string.Format("{0}, {1}", current, next))

                                };
                    ASPxGridView1.DataSource = query;
                    ASPxGridView1.DataBind();
                }   
            }

I get the following error when I try the above code:

LINQ to Entities does not recognize the method 'System.String Aggregate[String](System.Collections.Generic.IEnumerable1[System.String], System.Func3[System.String,System.String,System.String])' method, and this method cannot be translated into a store expression.

When I try:

 if (!IsPostBack)
                {
                    using (var context = new ALEntities())
                    {
                        var query = from c in context.CompanyNotices.Include("Locations")
                                    select new 
                                    { 
                                        c.CompanyNoticeHeading, 
                                        c.CompanyNoticeText,
                                        c.IsHR,
                                        locations = (from l in c.Locations select l.LocationName)

                                    };
                        ASPxGridView1.DataSource = query;
                        ASPxGridView1.DataBind();
                    }   
                }

The data within the locations column on the gridview appears as:

System.Collections.Generic.List`1[System.String]

Does anyone know how do I aggregate the LocationName to appear for one CompanyNotice?

Thanks in advance.

解决方案

you could this ...

using (var context = new ALEntities()) 
                    { 
                        var query = from c in context.CompanyNotices.Include("Locations") 
                                    select new  
                                    {  
                                        c.CompanyNoticeHeading,  
                                        c.CompanyNoticeText, 
                                        c.IsHR, 
                                        locations = (from l in c.Locations select l.LocationName) 

                                    }; 
var listed = query.ToList();
var commaListed = listed.Select ( a=> new { a.CompanyNoticeHeading, a.CompanyNoticeText,
commaLines =  a.locations.Aggregate((s1, s2) => s1 + "," + s2)});

then bind commaListed to your datagrid

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