LINQ实体中不支持LINQ表达式节点'arrayindex'。 [英] LINQ expression node 'arrayindex' is not supported in LINQ to entities.

问题描述

我正在尝试做一个简单的选择where语句来获取代码alfa2 = country [i]在循环中的国家名称。



我尝试过：

I am trying to do a simple select where statement to get the name of country where the code alfa2 = country[i] in a loop.

What I have tried:

OFFERS_COUNTRIES c = new OFFERS_COUNTRIES();
    for (int i = 0; i < countryId.Length; i++)
       {
          var nnn = from e in db.COUNTRIES where e.alfa2 == countryId[i] select e.countryName;
          c.country_name = nnn.ToString();

          db.OFFERS_COUNTRIES.Add(c);
          db.SaveChanges();
        }

我收到此行中的例外情况：

I receive the exception in this line:

c.country_name = nnn.ToString();

有什么问题？

推荐答案

试试这个：

Try this:

for (int i = 0; i < countryId.Length; i++)
{
    var countryID = countryId[i]; //<-- removes array reference from the linq query
    var nnn = from e in db.COUNTRIES where e.alfa2 == countryID select e.countryName;
    c.country_name = nnn.ToString();

    db.OFFERS_COUNTRIES.Add(c);
    db.SaveChanges();
}

在单个查询中检索国家/地区名称列表几乎肯定会更有效，并且只在添加后保存更改上下文中的所有要约：

It would almost certainly be more efficient to retrieve the list of country names in a single query, and to only save the changes after adding all of the offers to the context:

var countries = db.COUNTRIES
    .Where(e => countryId.Contains(e.alfa1))
    .Select(e => e.countryName)
    .AsEnumerable()
    .Select(name => new OFFERS_COUNTRIES 
    {
        country_name = name
    });

db.OFFERS_COUNTRIES.AddRange(countries);
db.SaveChanges();

这篇关于LINQ实体中不支持LINQ表达式节点'arrayindex'。的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！