运算符'&&'不能应用于类型为'bool'和'bool?'的操作数

问题描述：

尝试读取这样的dataContext类

Trying to read a dataContext class like this

var users = new List<User>();
var roles = new int[] { 1, 2 };
// here I need to get users who's role is in role (1, 2), hence above line
// and also I need to get user who's isValid field true, please note that isValid is SQL 'bit' field and is nullable
//This is what I am doing
foreach (var user in dataContext.Users
                                .Where(u => roles.Contains(u.RoleID.Value)
                                            && u.isValid ?? false == true)) // here '&&' part I'm struggling and getting above error
{
    users.Add(new User()
    {
         // Users Added in collection
    });
}

所以问题出在where子句中，我需要获取角色为(1,2)&&的用户. isValid == true，如果isValid为'null'，则将其设为false. 谢谢

So the question is in where clause I need to get user's who are in role(1,2) && isValid == true, if isValid is 'null' make it false. Thanks

答

您必须将其用括号括起来:

You have to wrap it in parentheses:

roles.Contains(u.RoleID.Value) && (u.isValid ?? false)

与(u.isValid?false)混淆，这并不意味着如果 u.isValid == null，然后将其设置为false，并在以下位置查找用户 u.isValid为假，这不是我想要的.

bit of confused with (u.isValid ?? false), does this not mean that if u.isValid == null then make it false and look for users where u.isValid is false, this is not what I want.

否，这仅表示将nulls视为false，并且所有用户都将isValid既不是null也不是false.之所以起作用，是因为??运算符将Nullable<bool>转换为bool，因此您可以将其与&&一起使用.我不喜欢它，我更喜欢稍后会理解的显式代码:

No, it just means that nulls are treated as false and that all users are taken which isValid is neither null nor false. It works because the ??-operator converts the Nullable<bool> to a bool, so you can use it with &&. I don't like it, i prefer explicit code that i understand later:

roles.Contains(u.RoleID.Value) && u.isValid.HasValue && u.isValid.Value

或更简单，通过将==-运算符与bool?一起使用:

or simpler by using the ==-operator with the bool?:

roles.Contains(u.RoleID.Value) && u.isValid == true

运算符'&&'不能应用于类型为'bool'和'bool?'的操作数

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