Question

我有两个系列。每个集合都包含特定类型的实例。我需要使用每个集合中实例的一个属性来连接这两个集合。问题是我将在运行时才知道要用于连接的属性。那么如何为动态Join编写LINQ查询呢？这是带有静态连接的LINQ查询的代码。在下面的示例代码中，您将注意到我正在使用MyTran.MyAmountUSD = YourTran.YourAmountUSD加入两个集合。但在实际情况中，我将知道在运行时仅使用哪个属性进行连接。所以有时我可能需要加入MyTran.MyAmountGBP = YourTran.YourAmountGBP。

class MyTran
{
    public int Id { get; set; }
    public double MyAmountUSD { get; set; }
    public double MyAmountGBP { get; set; }
}

class YourTran
{
    public int Id { get; set; }
    public double YourAmountUSD { get; set; }
    public double YourAmountGBP { get; set; }
}

class Program
{
    static void Main(string[] args)
    {
        List<MyTran> fMyTranList = new List<MyTran>();
        List<YourTran> fYourTranList = new List<YourTran>();

        fMyTranList.Add(new MyTran { Id = 1, MyAmountGBP = 100, MyAmountUSD = 1000 });
        fMyTranList.Add(new MyTran { Id = 2, MyAmountGBP = 101, MyAmountUSD = 2000 });

        fYourTranList.Add(new YourTran { Id = 11, YourAmountGBP=100, YourAmountUSD=1000 });
        fYourTranList.Add(new YourTran { Id = 12, YourAmountGBP = 102, YourAmountUSD = 3000 });

        var query = from fMyTrans in fMyTranList
                    join fYourTrans in fYourTranList
                         on fMyTrans.MyAmountUSD equals fYourTrans.YourAmountUSD
                    select new
                    {
                        MyId = fMyTrans.Id,
                        YourId = fYourTrans.Id,
                        MyAmtUSD = fMyTrans.MyAmountUSD,
                        MyAmtGBP = fMyTrans.MyAmountGBP,
                        YourAmtUSD = fYourTrans.YourAmountUSD,
                        YourAmtGBP = fYourTrans.YourAmountGBP
                    };

        foreach (var fMatch in query)
        {
            Console.WriteLine(fMatch);
        }
    }
}

Answer 1

解决此问题的第一个线索是使用lamda syntax为Join

重新编写联接

var query = fMyTranList.Join(fYourTranList,
               a => a.MyAmountGBP, 
               b => b.YourAmountGBP, 
               (c,d) => new
                    {
                        MyId = c.Id,
                        YourId = d.Id,
                        MyAmtUSD = c.MyAmountUSD,
                        MyAmtGBP = c.MyAmountGBP,
                        YourAmtUSD = d.YourAmountUSD,
                        YourAmtGBP = d.YourAmountGBP
                    });

直播：http://rextester.com/OGC85986

这应该清楚表明，制作这种动态需要传递给你的＆＃34; generic＆＃34;加入函数3函数

用于选择LHS密钥的Func<MyTran,TKey>函数
用于选择RHS密钥的Func<YourTran,TKey>函数
用于选择结果的Func<MyTran,YourTran,TResult>函数

所以从那里你可以使用反射来使这一切变得有点动态：

public static class DynamicJoinExtensions
{
    public static IEnumerable<dynamic> DynamicJoin(this IEnumerable<MyTran> myTran, IEnumerable<YourTran> yourTran, params Tuple<string, string>[] keys)
    {
        var outerKeySelector = CreateFunc<MyTran>(keys.Select(k => k.Item1).ToArray());
        var innerKeySelector = CreateFunc<YourTran>(keys.Select(k => k.Item2).ToArray());

        return myTran.Join(yourTran, outerKeySelector, innerKeySelector, (c, d) => new
        {
            MyId = c.Id,
            YourId = d.Id,
            MyAmtUSD = c.MyAmountUSD,
            MyAmtGBP = c.MyAmountGBP,
            YourAmtUSD = d.YourAmountUSD,
            YourAmtGBP = d.YourAmountGBP
        }, new ObjectArrayComparer());
    }

    private static Func<TObject, object[]> CreateFunc<TObject>(string[] keys)
    {
        var type = typeof(TObject);
        return delegate(TObject o)
        {
            var data = new object[keys.Length];
            for(var i = 0;i<keys.Length;i++)
            {
                var key = type.GetProperty(keys[i]);
                if(key == null)
                    throw new InvalidOperationException("Invalid key: " + keys[i]);
                data[i] = key.GetValue(o);
            }
            return data;
        };
    }

    private class ObjectArrayComparer : IEqualityComparer<object[]>
    {

        public bool Equals(object[] x, object[] y)
        {
            return x.Length == y.Length
                   && Enumerable.SequenceEqual(x, y);
        }

        public int GetHashCode(object[] o)
        {
            var result = o.Aggregate((a, b) => a.GetHashCode() ^ b.GetHashCode());
            return result.GetHashCode();
        }
    }
}

用于匹配您的示例的用法将是：

var query = fMyTranList.DynamicJoin(fYourTranList, 
               Tuple.Create("MyAmountGBP", "YourAmountGBP"));

但由于密钥为params，您可以按照自己的意愿传递：

var query = fMyTranList.DynamicJoin(fYourTranList, 
              Tuple.Create("MyAmountGBP", "YourAmountGBP"), 
              Tuple.Create("AnotherMyTranProperty", "AnotherYourTranProperty"));

实例：http://rextester.com/AAB2452

如何使用LINQ执行动态连接

1 个答案: