将具有lambda表达式的2个foreach循环转换为一个或两个lambda语句，以便为每个循环删除 [英] Convert 2 foreach loops which has lambda expressions to one or two lambda statements in order to remove for each loops

问题描述

我需要为每个循环转换2，如下所示为linq -

Hi,

I need to convert 2 for each loops which are shown as below to linq -

List<Company> res = new List<Company>();
          List<EmployeeCount> result = new List<EmployeeCount>();
          foreach (string s in indType)
          {
              List<Company> re = _entities.Company.Where(a => Convert.ToString(a.industry_id.ToLower()).Equals(s.ToLower().ToString())).ToList();
              res.AddRange(re);
          }

          foreach (Company r in res)
          {
              List<EmployeeCount> empCount = await _entities.EmployeeCount.Where(a => Convert.ToString(a.Company_ID.ToLower()).Equals(r.Company_id.ToLower())).Select((a => new EmployeeCount() { Company_ID = a.Company_ID, Industry_ID = a.Industry_ID, Company_Name = a.Company_Name, City = a.City, Number_Employees = a.Number_Employees })).ToListAsync();
              result.AddRange(empCount);
          }
          return result.AsQueryable();

我需要使用lambda表达式优化这些foreach循环以获取数据快速。请帮帮我。



我尝试过：



尝试如下 -



res.ForEach（i => i.company_id）.intersect（_entities.EmployeeCount.Select（i => i.company_id）。 ToList（）;



显示它只返回List< string>，我需要List< employeecount>。无法选择EmployeeCount实体的值。

I need to optimize these foreach loops using lambda expressions in order to fetch the data fastly. Please help me on this.

What I have tried:

tried like below -

res.ForEach(i => i.company_id).intersect(_entities.EmployeeCount.Select(i => i.company_id).ToList();

its showing it returns List<string> only, I need List<employeecount>. Unable to select the values of EmployeeCount entity.

推荐答案

并不完全清楚你要做的是什么，但假设你正在使用实体框架，这样的事情应该有效：

Not entirely clear what you're trying to do, but assuming you're using Entity Framework, something like this should work:

return _entities.EmployeeCount.Where(ec => indType.Contains(ec.Industry_ID));

如果 EmployeeCount Industry_ID 列c>实体与 Company 实体上的同名列不匹配，那么您需要一个导航属性：

If the Industry_ID column on the EmployeeCount entity doesn't match the column of the same name on the Company entity, then you'll need a navigation property:

return _entities.EmployeeCount.Where(ec => indType.Contains(ec.Company.Industry_ID));

如果 EmployeeCount 集合未返回 EmployeeCount的实例 class，然后添加 .Select（...）到最后：

If the EmployeeCount set doesn't return an instance of your EmployeeCount class, then add a .Select(...) to the end:

return _entities.EmployeeCount
    .Where(ec => indType.Contains(ec.Industry_ID))
    .Select(ec => new EmployeeCount
    {
        Company_ID = ec.Company_ID, 
        Industry_ID = ec.Industry_ID, 
        Company_Name = ec.Company_Name, 
        City = ec.City, 
        Number_Employees = ec.Number_Employees,
    });

如果您正在寻找速度，循环是可行的方法。



我会带走al看看你的数据。每家公司都有员工人数吗？如果他们这样做，则不需要第一个循环。所有第一个循环都是根据行业ID获取公司ID列表，然后您在第二个循环中使用该行业ID，该行业ID也具有行业ID。



您是否也需要创建一个EmployeeCount的新实例，还是可以使用原始对象？使用原版将节省时间而不是创建新实例。



如果第一个循环无关紧要且你不需要，我会做类似的事情对象的副本

If you are looking for speed, loops are the way to go.

I would take a look at your data. Does every company have an employee count? If they do then there is not a need for the first loop. All the first loop does is get a list of Company IDs based on Industry ID that you are then using in the second loop which also has Industry ID.

Do you also need to make a new instance of EmployeeCount or can you use the original object? Using the original will save time rather than creating a new instance.

I would do something similar to this if the first loop doesn't matter and you do not need a copy of the object

List<EmployeeCount> result = new List<EmployeeCount>();

foreach (EmployeeCount c in _entities.EmployeeCount)
{
    if (indType.Contains(c.industry_id))
    {
        result.Add(c);
    }
}

return result;

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