C# Linq 从列表中返回一个新对象
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Linq to return a new object with a selection from the list
提问by flip
I have the following object structure:
我有以下对象结构：
public class A
{
public string ID { get; set; }
public IList<B> Values { get; set; }
}
public class B
{
public string Code { get; set; }
public string DisplayName { get; set; }
}
public List<A> IDs;
I would like to use Linq to query B and return a single instance of A with the single element of B in values. Is that possible? I currently do this with a foreach but I am thinking Linq would be neater.
我想使用 Linq 查询 B 并返回 A 的单个实例，其中 B 的单个元素在值中。那可能吗？我目前使用 foreach 执行此操作，但我认为 Linq 会更简洁。
foreach (A a in IDs)
{
foreach (B b in a.Values)
{
if (b.Code == code)
{
return (new A()
{
ID = a.ID,
Values = new List<B>()
{
new B()
{
Code = b.Code,
DisplayName = b.DisplayName
}
}
});
}
}
}
采纳答案by Cédric Bignon
In LINQ with the query-syntax:
在带有查询语法的 LINQ 中：
return (from a in IDs
from b in a.Values
where b.Code == code
select (new A
{
ID = a.ID, Values = new List<B>
{
new B
{
Code = b.Code,
DisplayName = b.DisplayName
}
}
})).FirstOrDefault();
回答by Hogan
Run the following in LinqPad (LinqPad.com)
在 LinqPad (LinqPad.com) 中运行以下命令
void Main()
{
List<A> IDs= new List<A>() {
new A() { ID = "1", Values = new List<B>() {
new B { Code = "1", DisplayName = "1"},
new B { Code = "2", DisplayName = "2"},
new B { Code = "3", DisplayName = "3"} } },
new A() { ID = "4", Values = new List<B>() {
new B { Code = "4", DisplayName = "4"},
new B { Code = "5", DisplayName = "5"},
new B { Code = "6", DisplayName = "6"} } },
new A() { ID = "7", Values = new List<B>() {
new B { Code = "7", DisplayName = "7"},
new B { Code = "8", DisplayName = "8"},
new B { Code = "9", DisplayName = "9"} } }
};
A result = IDs.Where(a => a.Values.Any(b=> b.Code == "4")).FirstOrDefault();
result.Dump();
result = IDs.FirstOrDefault(a => a.Values.Any(b=> b.Code == "8"));
result.Dump();
}
// Define other methods and classes here
public class A
{
public string ID { get; set; }
public IList<B> Values { get; set; }
}
public class B
{
public string Code { get; set; }
public string DisplayName { get; set; }
}
You get this:
你得到这个：
Prior edits follow:
之前的编辑如下：
With the edit to the question:
随着对问题的编辑：
A result = IDs.Where(a => a.Values.Any(b=> b.Code == code)).FirstOrDefault();
Original answer below
原答案如下
The following will return the first A element where ID = id
下面将返回第一个 A 元素，其中 ID = id
A result = IDs.Where(a => a.ID == id).FirstOrDefault();
This makes it a list
这使它成为一个列表
List<A> result = IDs.Where(a => a.ID == id).FirstOrDefault().ToList();
回答by Abhishek Jain
Try this:
尝试这个：
IDs.Where(a=>a.ID = id)
.Select(a => new A()
{
ID = a.ID,
Values = new List<B>()
{
new B()
{
Code = a.Values.First().Code,
DisplayName = a.Values.First().DisplayName
}
}
});
