LINQ (C#) 中的限定符运算

  • 项目

限定符运算返回一个 Boolean 值，该值指示序列中是否有一些元素满足条件或是否所有元素都满足条件。

下图描述了两个不同源序列上的两个不同限定符运算。 第一个运算询问是否有任何元素为字符“A”。 第二个运算询问是否所有元素都为字符“A”。 这两种方法在此示例中都返回 true。

LINQ 限定符运算

下节列出了执行限定符运算的标准查询运算符方法。

方法

方法名 描述 C# 查询表达式语法 更多信息
全部 确定是否序列中的所有元素都满足条件。 不适用。 Enumerable.All
Queryable.All
任意 确定序列中是否有元素满足条件。 不适用。 Enumerable.Any
Queryable.Any
包含 确定序列是否包含指定的元素。 不适用。 Enumerable.Contains
Queryable.Contains

查询表达式语法示例

全部

以下示例使用 All 检查所有字符串是否为特定长度。

class Market
{
    public string Name { get; set; }
    public string[] Items { get; set; }
}

public static void Example()
{
    List<Market> markets = new List<Market>
    {
        new Market { Name = "Emily's", Items = new string[] { "kiwi", "cheery", "banana" } },
        new Market { Name = "Kim's", Items = new string[] { "melon", "mango", "olive" } },
        new Market { Name = "Adam's", Items = new string[] { "kiwi", "apple", "orange" } },
    };

    // Determine which market have all fruit names length equal to 5
    IEnumerable<string> names = from market in markets
                                where market.Items.All(item => item.Length == 5)
                                select market.Name;

    foreach (string name in names)
    {
        Console.WriteLine($"{name} market");
    }

    // This code produces the following output:
    //
    // Kim's market
}

任意

以下示例使用 Any 检查所有字符串是否以“o”开头。

class Market
{
    public string Name { get; set; }
    public string[] Items { get; set; }
}

public static void Example()
{
    List<Market> markets = new List<Market>
    {
        new Market { Name = "Emily's", Items = new string[] { "kiwi", "cheery", "banana" } },
        new Market { Name = "Kim's", Items = new string[] { "melon", "mango", "olive" } },
        new Market { Name = "Adam's", Items = new string[] { "kiwi", "apple", "orange" } },
    };

    // Determine which market have any fruit names start with 'o'
    IEnumerable<string> names = from market in markets
                                where market.Items.Any(item => item.StartsWith("o"))
                                select market.Name;

    foreach (string name in names)
    {
        Console.WriteLine($"{name} market");
    }

    // This code produces the following output:
    //
    // Kim's market
    // Adam's market
}

包含

以下示例使用 Contains 检查所有数组是否具有特定元素。

class Market
{
    public string Name { get; set; }
    public string[] Items { get; set; }
}

public static void Example()
{
    List<Market> markets = new List<Market>
    {
        new Market { Name = "Emily's", Items = new string[] { "kiwi", "cheery", "banana" } },
        new Market { Name = "Kim's", Items = new string[] { "melon", "mango", "olive" } },
        new Market { Name = "Adam's", Items = new string[] { "kiwi", "apple", "orange" } },
    };

    // Determine which market contains fruit names equal 'kiwi'
    IEnumerable<string> names = from market in markets
                                where market.Items.Contains("kiwi")
                                select market.Name;

    foreach (string name in names)
    {
        Console.WriteLine($"{name} market");
    }

    // This code produces the following output:
    //
    // Emily's market
    // Adam's market
}

请参阅