如何初始化ConcurrentDictionary？错误:"无法访问私有方法'在此处添加'

Question

我有一个静态类,我在其中使用字典作为查找表来映射.NET类型和SQL类型.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方法,它传入一个.NET类型,它使用这个字典返回相应的MS SQL Server类型的字符串值.但是,由于这被用作进行数据库查询的查找表,我认为将其作为一个有意义ConcurrentDictionary.我改成了:

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"}
};

但现在它强调了内部的所有红色{}(即所有键值对ConcurrentDictionary),错误是:

无法在此处访问私有方法"添加"

我不认为这是因为我将其初始化为private static readonly,因为我只是通过制作public static版本进行测试而且我得到了相同的错误.

Answer 1

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Dictionary Initializers.

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"
    };

示例 https://dotnetfiddle.net/9ZgjsR

Answer 2

只有当集合具有Add适当签名和可访问性的方法时,您用于填充集合的集合初始值设定项才有效. ConcurrentDictionary没有公共Add方法,因此您将无法使用集合初始值设定项.

您可以通过将IEnumerable<KeyValuePair<TKey, TValue>>一个参数作为参数传递给构造函数来提供一些初始数据,或者您可以在创建后在循环中调用TryAdd(或AddOrUpdate,或者名称中的任何其他方法Add)ConcurrentDictionary.

Answer 3

作为 Servy 接受的答案的代码示例，为了ConcurrentDictionary在实例化时初始化 a ，您可以将实现类型IEnumerable（如 a List）的KeyValuePair类型传递给构造函数：

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