将两个列表转换为字典

Question

我正在寻找一个可以替换我的两个循环的LINQ函数来产生类似的结果:

public class Outer {
    public long Id { get; set; }
}

public class Inner {
    public long Id { get; set; }
    public long OuterId { get; set; }
}

var outers = new List<Outer>();
var inners = new List<Inner>();
// add some of each object type to the two lists

// I'd like to replace this code with a LINQ-style approach
var map = new Dictionary<long, long>();
foreach (Outer outer in outers) {
    foreach (Inner inner in inners.Where(m => m.OuterId == outer.Id)) {
        map.Add(inner.Id, outer.Id);
    }
}

Answer 1

var map = inners
          .ToDictionary(a => a.Id, 
                        a => outers
                             .Where(b => b.Id == a.OuterId)
                             .Select(b => b.Id)
                             .First()
                        );