从列表中获取对象 <object> 其中property为null且o​​rder为最低

Question

I have a class:

public class Menu
{
    public Menu()
    {

    }

    public string Value { get; set; }
    public int Order { get; set; }
}

and then:

 List<Menu> menus = new List<Menu>() // contains 10 items let's say.

How can I get the item from the list where the Value == null and the Order is the smallest values among items?

Example:

Menu items can have an order like this: 10, 20, 30, 40, 50 ...

There are no items with the same order, each item has a unique number value.

I am interested to get the Menu when the Order is the smallest one and Value is null. In this case the item where Order is 10 and Value null.

Answer 1

Use Linq for that:

 var result = menus.Where(x => x.Value == null).OrderBy(x => x.Order).FirstOrDefault();

Where takes only object with Value == null

OrderBy orders them by Order property

FirstOrDefault takes first value or returns null if there are none that match the query

 // This can be written in a shorter form
 var resultWithShorterLinq = menus.OrderBy(x => x.Order).FirstOrDefault(x => x.Value == null);

Both ways are equivalent, because with Linq you first build query with methods like Where, OrderBy, OrderByDescending... And only execute it when you call one of these methods:

query.ToList();
query.ToArray();
query.First();
query.FirstOrDefault();
etc...

And when using FirstOrDefault, don't forget to check if there is result found by checking if it's not null

if(result != null){
    // The result is found :)
}
else {
    // No results :(
}

Answer 2

You can use LINQ to achieve that:

var menuItem = menus.Where(m => m.Value == null).OrderBy(m=>m.Order).First();

This assumes that there is at least one item in the list. If there can be no items you can use .FirstOrDefault() instead.

Answer 3

Using LINQ ordering your List by Order then getting the first that has a null value

Menu mn = menus.OrderBy(x => x.Order).FirstOrDefault(m => m.Value == null);
if(mn != null)
{
    // Got it
}
else
{
    // No match for your condition
}