Question

是否可以将此代码重写为LINQ？我是linq的新手，似乎很难理解。

String ChildBelowList = "";

    if (!Childbelow.isEmpty()) {
        for (int iCB = 0; iCB < Childbelow.size(); iCB++) {

            ChildBelowList = ChildBelowList += Childbelow.get(iCB) + ",";



        }
        ChildBelowList = ChildBelowList.replaceAll("(^(\\s*?\\,+)+\\s?)|(^\\s+)|(\\s+$)|((\\s*?\\,+)+\\s?$)", "");

        tv_childbelow.setText(ChildBelowList);

    } else {
        ll_childbelow.setVisibility(View.GONE);
    }

Answer 1

由于条件EarningsList.Add（）

，第一部分不易转换

但你可以很容易地重写最后2个。

假设<html> <head> <title>Page Title</title> <script src="https://ajax.aspnetcdn.com/ajax/jQuery/jquery-3.3.1.min.js"></script> </head> <body> <span class="outer"> <label class="lb">hi there</label> <input class="in" type="text"/> </span> <span class="outer"> <label class="lb">hi there</label> <input class="in" type="text"/> </span> <span class="outer"> <label class="lb">hi there</label> <input class="in" type="text"/> </span> </body> </html>完全符合其说法，您可以使用AddMoney()。否则，省略Sum（）并在金额列表上运行单独的foreach。这样可以减少Linq。

Sum()

Answer 2

不知道.AddMoney方法到底能做什么：

var query =
    from employee in EmployeeList
    let earnings = new Earnings(employee.Name, employee.LastName, employee.Bank, employee.Account)
    from item in ProductList
    from product in item.Products
    where product.EmployeeName == employee.Name
    where product.EmployeeLastName == employee.LastName
    group product.Count * product.Price by earnings;

List<Earnings> EarningsList =
    query
        .Aggregate(new List<Earnings>(), (a, x) =>
        {
            a.Add(x.Key);
            foreach (var y in x)
            {
                x.Key.AddMoney(y);
            }
            return a;
        });

如果.AddMoney只是算术地加钱，那么你可以这样做：

List<Earnings> EarningsList =
    query
        .Aggregate(new List<Earnings>(), (a, x) =>
        {
            a.Add(x.Key);
            x.Key.AddMoney(x.Sum());
            return a;
        });

只是一个小小的音符。您正在使用double来代表金钱。最好使用decimal，因为这有助于防止计算中的舍入错误。

Answer 3

我认为如果你刚刚使用LINQ（没有foreach），这就是你想要的。这应该与IQueryable兼容，你真的不想在IQueryable上做foreach。

var newEarnings = from employee in EmployeeList
                              select new Earnings
                              {
                                  Name = employee.Name,
                                  LastName = employee.LastName,
                                  Bank = employee.Bank,
                                  Account = employee.Account,
                                  Money = (from daysData in ProductList
                                           from product in daysData.Products
                                           where employee.Name == product.EmployeeName && employee.LastName == product.EmployeeLastName
                                           select product).Sum(p => p.Count * p.Price)
                              };

            EarningsList = EarningsList.Union(newEarnings).ToList();

现在关于规范化。我猜你是为了在某种网格中展示它而制作了这样的POCO模型。你真的不应该让你的UI决定你的数据模型是什么样的。可能有其他原因要做到这一点，但它们与性能有关，我不认为你需要担心这只是喷气机。所以这是我对如何改变它的建议。

将Id属性添加到所有类。这总是一个好主意不管你在做什么。这可以是随机字符串或自动字符串增量，只是为了拥有一个独特的值，所以你可以玩这个对象。
在您的课程中添加参考属性。不要复制值员工对产品和收益。只需添加类型的属性员工和/或添加EmployeeId属性

所以你的POCO看起来应该是这样的

public class Employee
{
    //It can be a Guid, string or what ever. I am not nesseserly recomending using Guids and you should look into this a bit more   
    public Guid Id { get; set; }

    public string Name { get; set; }

    public string LastName { get; set; }

    public string Bank { get; set; }

    public string Account { get; set; }
}

public class DaysData
{
    public Guid Id { get; set; }

    public IEnumerable<Product> Products { get; set; }
}

public class Product
{
    public Guid Id { get; set; }

    public Guid EmployeeId { get; set; }

    public Employee Employee { get; set; }

    public double Count { get; set; }

    public double Price { get; set; }
}

public class Earnings
{
    public Guid Id { get; set; }

    public Guid EmployeeId { get; set; }

    public Employee Employee { get; set; }

    public double Money { get; set; }
}

和查询

var newEarnings = from employee in EmployeeList
                          select new Earnings
                          {
                              Id = Guid.NewGuid(),
                              EmployeeId = employee.Id,
                              Employee = employee,
                              Money = (from daysData in ProductList
                                       from product in daysData.Products
                                       where employee.Id == product.EmployeeId
                                       select product).Sum(p => p.Count * p.Price)
                          };

一旦你尝试实现数据持久性，无论你使用EF，Mongo，Elsatic，AzureTables还是其他任何东西，即使是简单的文件保存，这对你也会有很大的帮助。

嵌套的foreach循环到LINQ

3 个答案: