如何在 LINQ 中列为空时用空 space 替换“-”

Question

这里我有下面的 Linq 查询，其中有员工持续时间列。当 StartDate 或 EndDate 为空时，如何删除“-”。只有当两者都不为空时，我才想要“-”。

var query = from r in db.Employee 
            select new 
            {
                Name = r.Name,
                EmployeeDuration = r.StartDate +" - "+ r.EndDate
            }

Answer 1

EmployeeDuration = r.StartDate != null && r.EndDate != null ? r.StartDate + " - " + r.EndDate : String.Empty;

Answer 2

您可以使用条件运算符。

var query = from r in db.Employee 
        select new 
        {
            Name = r.Name,
            EmployeeDuration = r.StartDate != null && r.EndDate != null 
                ? r.StartDate + " - " + r.EndDate
                : r.StartDate ?? r.EndDate
        }

输出

When nothing is null   = 18.01.2017 18:00 - 18.01.2017 19:00
When StartDate is null = 18.01.2017 19:00
When EndDate is null   = 18.01.2017 18:00

或者另一种方法是这样。

var query = from r in db.Employee 
        select new 
        {
            Name = r.Name,
            EmployeeDuration = 
                (r.StartDate ?? "?") +
                " - " +
                (r.EndDate ?? "?")
        }

输出

When nothing is null   = 18.01.2017 18:00 - 18.01.2017 19:00
When StartDate is null = ? - 18.01.2017 19:00
When EndDate is null   = 18.01.2017 18:00 - ?

Answer 3

var query = from employee in db.Employee 
            let areDatesNull = employee.StartDate == null
                            || employee.EndDate == null
            let duration = areDatesNull
                         ? ""
                         : $"{employee.StartDate} - {employee.EndDate}"
            select new 
            {
                Name = employee.Name,
                EmployeeDuration = duration
            }

Answer 4

像这样：

var query = from r in db.Employee
    select new
    {
        Name = r.Name
        ,
        EmployeeDuration =
        r.StartDate + ((r.StartDate == null || r.EndDate == null) ? string.Empty : " - ") + r.EndDate
    };

如何在 LINQ 中列为空时用空 space 替换“-”

How to replace "-" with empty space when columns are null in LINQ

c#

linq

select

string-concatenation