基于输入枚举参数选择列

Question

我有

Id | UserId | GoogleEnabled | FacebookEnabled | TwitterEnabled 

在代码中，我要选择{provider}Enabled值的价值列的表 - 输入枚举

enum Provider 
{ 
    Google, 
    Facebook, 
    Twitter 
} 

private async Task CheckSettingsAsync(ISeedSession<IDbSession> seedSession, IUserInfo user, Provider provider){ 
... 
var userSettingsTask = seedSession 
       .Query<UserSettings>() 
       .Where(us => us.UserId == user.UserId) 
       .Select(us => us.GoogleEnabled) // if provider value is "Google" 
       .SingleAsync(); 
... 
} 

true/false基地是否有任何模式/解决方案比创建一些switch来选择我的价值？

Answer 1

您可以手动构建表达us => us.GoogleEnabled，像这样：

var argument = Expression.Variable(typeof(UserSettings)); 
// assuming `provider` is enum with values "Google" etc 
var accessor = (Expression<Func<UserSettings, bool>>) Expression.Lambda(
    Expression.PropertyOrField(argument, provider.ToString() + "Enabled"), argument); 

，然后用它是这样的：

var userSettingsTask = seedSession 
    .Query<UserSettings>() 
    .Where(us => us.UserId == user.UserId) 
    .Select(accessor) // < here 
    .SingleAsync();