c# - 如何从 Web.config 获取常量字符串？

Question

为了在 Entity Framework 应用程序中进行授权，我编写了此类来检查当前用户是否属于指定角色。

public class AuthorizeDesignatedRoles : AuthorizeAttribute {

        public const string DELETE = System.Configuration.ConfigurationManager.AppSettings["GroupAuthorizedForDeleteAction"].ToString();
        public string DesignatedRoles { get; set; }

        protected override bool IsAuthorized(System.Web.Http.Controllers.HttpActionContext actionContext) {
            bool isAuthorizedBase = base.IsAuthorized(actionContext);
            if (!isAuthorizedBase)
                return false;


            string[] roles = DesignatedRoles.Split(';');  // Multiple roles can be seperated by a semicolon ;
            foreach (string role in roles) {
                if (System.Web.Security.Roles.IsUserInRole(role))
                    return true;
            }
            return false;
        }

    }

现在我可以只允许具有指定角色的用户执行 Controller 操作。

[AuthorizeDesignatedRoles(DesignatedRoles = AuthorizeDesignatedRoles.DELETE)]
public HttpResponseMessage DeleteThisAndThat(long id) { ... }

问题是我不想把指定的DELETE组的名字放在代码里而是放在web.config文件里。通过这样做，Visual Studio 会提示它不再是常量字符串。

如何使它再次成为常量字符串？

编辑:当我省略 const 关键字并改用 DELETE static readonly 时，编译器说 An attribute argument must可以是属性参数类型的常量表达式、typeof表达式或数组创建表达式。

Answer 1

如何将 AppSettings 键存储在常量中并在 IsAuthorized 方法中获取它的值:

public class AuthorizeDesignatedRoles : AuthorizeAttribute
{
    public const string DELETE = "GroupAuthorizedForDeleteAction";

    public string DesignatedRoles { get; set; }

    protected override bool IsAuthorized(System.Web.Http.Controllers.HttpActionContext actionContext) {
    {
        // ...

        string[] roles = DesignatedRoles.Split(';')
                                        .Select(s => ConfigurationManager.AppSettings[s].ToString())
                                        .ToArray();

        foreach (string role in roles)
        {
            // ...
        }
    }
}