具有复杂类型的多个属性的 GroupBy

Question

我写了一个 GroupBy 语句，如下所示：

var aggregated = sitesWithLive
    .GroupBy(s => new {s.SiteRefNum, s.SiteRefName, s.Address})
    .Select(g =>
        new Site
        {
            SiteRefNum = g.Key.SiteRefNum,
            SiteRefName = g.Key.SiteRefName,
            Address = g.Key.Address,
            ContractLive = g.Max(x => x.ContractLive)
        });

在分组中是Address哪个是复杂类型：

public class Address
{
    public string Name { get; set; }
    public string Line1 { get; set; }
    public string Line2 { get; set; }
    public string Line3 { get; set; }
    public string Line4 { get; set; }
    public string PostCode { get; set; }

    public bool IsEmpty()
    {
        return GetType().GetProperties()
            .Where(a => a.GetValue(this) is string)
            .Select(a => (string)a.GetValue(this))
            .All(string.IsNullOrEmpty);
    }

    public override string ToString()
    {
        var addr = Line1 + "," + Line2 + "," + Line3 + "," + Line4 + "," + PostCode;
        var address = Regex.Replace(addr, @"^,+|,{2,}|,(?=[\w.])", ", ");
        return address;
    }
}

但是，这不能按地址正确分组，而是为每个元素返回一个单独的组。

我的理解是，要按复杂类型分组，您必须提供一个，IEqualityComparer因此我创建了以下内容：

public class AddressComparer : IEqualityComparer<Address>
{
    public bool Equals(Address x, Address y)
    {
        return x.ToString() == y.ToString();
    }

    public int GetHashCode(Address obj)
    {
        return 1;
    }
}

并像这样提供它（上面的子集）：

var aggregated = sitesWithLive.GroupBy(s => new {s.SiteRefNum, s.SiteRefName, s.Address}, new AddressComparer())
...

然而，这给了我

无法从用法推断出类型参数。尝试明确指定类型参数。

我对下一步感到茫然，这种分组肯定不会太难吗？

Answer 1

Enumerable.GroupBy允许您为键传递自定义相等比较器。但是，在你的情况的关键不是一个Address对象-它包含以下三个属性的匿名对象- SiteRefNum，SiteRefName和Address。当然通过AddressComparer来比较这样的键会导致错误。

你的第一个问题是使用复杂对象作为关键属性。如果不覆盖对象的方法Equals和GetHashCode方法Address，则所有地址都将通过引用进行比较。对于每个地址实例，这当然是不同的。您可以提供Equals和GetHashCode实现来比较地址。

或者您可以修改您的查询以使用地址字符串进行分组：

var aggregated = 
    from s in sitesWithLive
    group s by new {
       s.SiteRefNum,
       s.SiteRefName,
       Address = s.Address.ToString() // here we group by string
    } into g
    select new Site
    {
        SiteRefNum = g.Key.SiteRefNum,
        SiteRefName = g.Key.SiteRefName,
        Address = g.First().Address, // here we just get first address object
        ContractLive = g.Max(x => x.ContractLive)
    };

您可以使用方法语法进行查询，但我发现声明式查询语法更具可读性:)