我有一个静态类，我在其中使用字典作为查找表以在 .NET 类型和 SQL 类型之间进行映射。这是一个这样的字典的例子:

private static readonly Dictionary<Type, string> SqlServerMap = new Dictionary<Type, string>
{
    {typeof (Boolean), "bit"},
    {typeof (Byte[]), "varbinary(max)"},
    {typeof (Double), "float"},
    {typeof (Byte), "tinyint"},
    {typeof (Int16), "smallint"},
    {typeof (Int32), "int"},
    {typeof (Int64), "bigint"},
    {typeof (Decimal), "decimal"},
    {typeof (Single), "real"},
    {typeof (DateTime), "datetime2(7)"},
    {typeof (TimeSpan), "time"},
    {typeof (String), "nvarchar(MAX)"},
    {typeof (Guid), "uniqueidentifier"}
};

然后我在下面有一个公共(public)方法，它传入一个 .NET 类型，它使用这个字典返回相应 MS SQL Server 类型的字符串值。但是，由于它被用作进行数据库查询的查找表，我认为将它设为 ConcurrentDictionary 是有意义的。我将其更改为:

private static readonly IDictionary<Type, string> SqlServerMap = new ConcurrentDictionary<Type, string>
{
    {typeof (Boolean), "bit"},
    {typeof (Byte[]), "varbinary(max)"},
    {typeof (Double), "float"},
    {typeof (Byte), "tinyint"},
    {typeof (Int16), "smallint"},
    {typeof (Int32), "int"},
    {typeof (Int64), "bigint"},
    {typeof (Decimal), "decimal"},
    {typeof (Single), "real"},
    {typeof (DateTime), "datetime2(7)"},
    {typeof (TimeSpan), "time"},
    {typeof (String), "nvarchar(MAX)"},
    {typeof (Guid), "uniqueidentifier"}
};

但现在它在 {}(即 ConcurrentDictionary 的所有键值对)中用红色下划线，错误是:

Cannot access private method 'Add' here

我不认为这是因为我将其初始化为private static readonly，因为我刚刚通过制作public static版本进行了测试，但我得到了同样的错误。

最佳答案

试试这个

private static readonly IDictionary<Type, string> SqlServerMap =
    new ConcurrentDictionary<Type, string>(
        new Dictionary<Type, string>()
        {
            {typeof(Boolean ), "bit"             },
            {typeof(Byte[]  ), "varbinary(max)"  },
            {typeof(Double  ), "float"           },
            {typeof(Byte    ), "tinyint"         },
            {typeof(Int16   ), "smallint"        },
            {typeof(Int32   ), "int"             },
            {typeof(Int64   ), "bigint"          },
            {typeof(Decimal ), "decimal"         },
            {typeof(Single  ), "real"            },
            {typeof(DateTime), "datetime2(7)"    },
            {typeof(TimeSpan), "time"            },
            {typeof(String  ), "nvarchar(MAX)"   },
            {typeof(Guid    ), "uniqueidentifier"}
        }
    );

更新:如果您使用的是 C#6(Roslyn 2.0 编译器)，则可以使用新的字典初始化器。

private static readonly IDictionary<Type, string> SqlServerMap =
    new ConcurrentDictionary<Type, string>
    {
        [typeof(Boolean )] = "bit"             ,
        [typeof(Byte[]  )] = "varbinary(max)"  ,
        [typeof(Double  )] = "float"           ,
        [typeof(Byte    )] = "tinyint"         ,
        [typeof(Int16   )] = "smallint"        ,
        [typeof(Int32   )] = "int"             ,
        [typeof(Int64   )] = "bigint"          ,
        [typeof(Decimal )] = "decimal"         ,
        [typeof(Single  )] = "real"            ,
        [typeof(DateTime)] = "datetime2(7)"    ,
        [typeof(TimeSpan)] = "time"            ,
        [typeof(String  )] = "nvarchar(MAX)"   ,
        [typeof(Guid    )] = "uniqueidentifier"
    };

例子 https://dotnetfiddle.net/9ZgjsR

关于c# - 如何初始化 ConcurrentDictionary？错误 : "Cannot access private method ' Add' here"，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31815456/