C# 允许使用 PhoneAttribute 或 UrlAttribute 标记的字段为空字符串
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Allow empty strings for fields marked with PhoneAttribute or UrlAttribute
提问by Nu-hin
I'm using CodeFirst Entitty framework 5. I have a class representing a user.
我正在使用 CodeFirst Entitty 框架 5。我有一个代表用户的类。
public class User
{
[Key]
public int UserId { get; set; }
[Url]
[DataType(DataType.Url)]
[Required(AllowEmptyStrings= true)]
public string WebSite { get; set; }
[Phone]
[DataType(DataType.PhoneNumber)]
[Required(AllowEmptyStrings = true)]
public string Phone { get; set; }
[Phone]
[DataType(DataType.PhoneNumber)]
[Required(AllowEmptyStrings = true)]
public string Fax { get; set; }
}
I like the validation mechanics for Phoneand Urlattributes a lot, but unfortunately validation fails when fields marked with these attributes are empty strings which I actually want to allow. [Required(AllowEmptyStrings = true)]doesn't seem to work with Phoneor Urlattributes. The same seems to apply to some other DataAnnotations attributes like EmailAddress.
我非常喜欢Phone和Url属性的验证机制，但不幸的是，当标有这些属性的字段是我真正想要允许的空字符串时，验证会失败。[Required(AllowEmptyStrings = true)]似乎不适用于Phone或Url属性。这似乎同样适用于其他一些 DataAnnotations 属性，例如EmailAddress.
Is there a way to allow empty strings for fields marked with such attributes?
有没有办法允许标有此类属性的字段为空字符串？
采纳答案by Neil Laslett
Validation attributes like [Phone]and [EmailAddress]will check any non-null string values. Because the stringtype is inherently nullable, empty strings passed to the ModelBinder are read as null, which passes the validation check.
验证属性像[Phone]并且[EmailAddress]将检查任何非空字符串值。因为string类型本质上是可为空的，所以传递给 ModelBinder 的空字符串被读取为null，从而通过了验证检查。
When you add the [Required]attribute, the string becomes effectively non-nullable. (If using Code First, EF will script a non-nullable database column.) The ModelBinder will now interpret a blank value as String.Empty- which will fail the attribute validation check.
当您添加该 [Required]属性时，该字符串实际上变为不可为空。（如果使用 Code First，EF 将编写不可为空的数据库列的脚本。）ModelBinder 现在会将空白值解释为String.Empty- 这将使属性验证检查失败。
So there is no way to allow emptystrings with validation attributes, but you can allow nullstrings. All you need to do is remove the [Required]attribute. Blank values will be nulland non-blank values will be validated.
所以没有办法允许带有验证属性的空字符串，但你可以允许空字符串。您需要做的就是删除该[Required]属性。空白值将null被验证，非空白值将被验证。
In my case, I am importing records from a CSV file, and had this problem because I was skipping the normal ModelBinder. If you are doing something unusual like this, be sure to include a manual check before saving to your data model:
就我而言，我正在从 CSV 文件导入记录，但遇到此问题是因为我跳过了普通的 ModelBinder。如果您正在做这样的不寻常的事情，请确保在保存到您的数据模型之前包括手动检查：
Email = (record.Email == String.Empty) ? null : record.Email
回答by user5791468
Use following two data annotations:
使用以下两个数据注释：
[Required(AllowEmptyStrings = true)]
[DisplayFormat(ConvertEmptyStringToNull = false)]
