如何解决Linq投影将列表平整为已定义字符串
| 我正在尝试合并并用逗号分隔(或空格)一个列表并对其进行投影。我下面有一些示例代码。public class Friend
{
public string Name { get; set; }
}
public class Person
{
public int PersonID { get; set; }
public string FirstName { get; set; }
public string Surname { get; set; }
List<Friend> Friends { get; set; }
}
public class ProjectedPerson
{
public int PersonID { get; set; }
public string FirstName { get; set; }
public string Surname { get; set; }
public string FriendsList { get; set; }
}
public class Test
{
public void Mytest()
{
var query = from p in MyDataStore.Person
select p;
var results = from q in query
select new ProjectedPerson
{
PersonID = q.PersonID,FirstName = q.FirstName,Surname = q.Surname,FriendsList = q.FriendsList.Concat() //??? How can I concat this and return a string
};
}
}
解决方法
string.Join是更好的方法,但是滥用LINQ太有趣了。
var query = (from p in MyDataStore.Person
select p).ToList(); // <-- bring into memory with ToList()
var results = from q in query
select new ProjectedPerson
{
PersonID = q.PersonID,FirstName = q.FirstName,Surname = q.Surname,FriendsList = q.Friends.Aggregate<Friend,string>(null,(accum,f) => accum + (accum == null ? accum : \",\") + f.Name)
};
, 使用string.Join(请注意,列表必须首先在内存中),以合并Friend对象中的选定属性。如果您使用的是.NET 3.5,则需要使用ToArray()以及字符串的重载。3.5中的联接需要一个数组。
var query = (from p in MyDataStore.Person
select p).ToList(); // <-- bring into memory with ToList()
var results = from q in query
select new ProjectedPerson
{
PersonID = q.PersonID,FriendsList = string.Join( \",\",q.Friends.Select( f => f.Name ) )
};
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