LINQ：“包含”和一个Lambda查询

我有一个List<BuildingStatus>电话buildingStatus。我想检查它是否包含其字符代码（由返回GetCharCode()）等于某个变量的状态v.Status。

遵循下面的（非编译）代码，有某种方法可以做到这一点？

buildingStatus.Contains(item => item.GetCharValue() == v.Status)

使用Any()代替Contains()：

buildingStatus.Any(item => item.GetCharValue() == v.Status)

Linq扩展方法Any可以为您服务...

buildingStatus.Any(item => item.GetCharValue() == v.Status)

这是您可以Contains用来实现所需目标的方法：

buildingStatus.Select(item => item.GetCharValue()).Contains(v.Status) 这将返回一个布尔值。

我不确定您在寻找什么，但是这个程序：

    public class Building
    {
        public enum StatusType
        {
            open,
            closed,
            weird,
        };

        public string Name { get; set; }
        public StatusType Status { get; set; }
    }

    public static List <Building> buildingList = new List<Building> ()
    {
        new Building () { Name = "one", Status = Building.StatusType.open },
        new Building () { Name = "two", Status = Building.StatusType.closed },
        new Building () { Name = "three", Status = Building.StatusType.weird },

        new Building () { Name = "four", Status = Building.StatusType.open },
        new Building () { Name = "five", Status = Building.StatusType.closed },
        new Building () { Name = "six", Status = Building.StatusType.weird },
    };

    static void Main (string [] args)
    {
        var statusList = new List<Building.StatusType> () { Building.StatusType.open, Building.StatusType.closed };

        var q = from building in buildingList
                where statusList.Contains (building.Status)
                select building;

        foreach ( var b in q )
            Console.WriteLine ("{0}: {1}", b.Name, b.Status);
    }

产生预期的输出：

one: open
two: closed
four: open
five: closed

该程序比较枚举的字符串表示形式，并产生相同的输出：

    public class Building
    {
        public enum StatusType
        {
            open,
            closed,
            weird,
        };

        public string Name { get; set; }
        public string Status { get; set; }
    }

    public static List <Building> buildingList = new List<Building> ()
    {
        new Building () { Name = "one", Status = "open" },
        new Building () { Name = "two", Status = "closed" },
        new Building () { Name = "three", Status = "weird" },

        new Building () { Name = "four", Status = "open" },
        new Building () { Name = "five", Status = "closed" },
        new Building () { Name = "six", Status = "weird" },
    };

    static void Main (string [] args)
    {
        var statusList = new List<Building.StatusType> () { Building.StatusType.open, Building.StatusType.closed };
        var statusStringList = statusList.ConvertAll <string> (st => st.ToString ());

        var q = from building in buildingList
                where statusStringList.Contains (building.Status)
                select building;

        foreach ( var b in q )
            Console.WriteLine ("{0}: {1}", b.Name, b.Status);

        Console.ReadKey ();
    }

我创建了此扩展方法，以将一个IEnumerable转换为另一个IEnumerable，但是我不确定它的效率如何。它可能只是在后台创建一个列表。

public static IEnumerable <TResult> ConvertEach (IEnumerable <TSource> sources, Func <TSource,TResult> convert)
{
    foreach ( TSource source in sources )
        yield return convert (source);
}

然后，您可以将where子句更改为：

where statusList.ConvertEach <string> (status => status.GetCharValue()).
    Contains (v.Status)

并跳过创建List<string>与ConvertAll ()开头。

如果我理解正确，则需要将“建筑物”列表中存储的类型（字符值）转换为“建筑物状态”列表中存储的类型（枚举）。

（对于建筑物列表//字符值//中的每个状态，该状态是否存在于建筑物状态列表//枚举值//中）

public static IQueryable<Building> WithStatus(this IQueryable<Building> qry,  
IList<BuildingStatuses> buildingStatus) 
{ 
    return from v in qry
           where ContainsStatus(v.Status)
           select v;
} 


private bool ContainsStatus(v.Status)
{
    foreach(Enum value in Enum.GetValues(typeof(buildingStatus)))
    {
        If v.Status == value.GetCharValue();
            return true;
    }

    return false;
}