Field Validation

Question

Hi

I have written below Annotation on a field . If it is required in another in will have to write it again

. Can we create only once thru class each Annotation separately or some other way so that it can be used in any class

[DataType(DataType.Text)]
[Required(ErrorMessage = "Description can not be blank.")]
[StringLength(25, ErrorMessage = "Max length should be less than or equal to 25.")]
[RegularExpression(@"^[a-zA-Z][a-zA-Z ]+$", ErrorMessage = "Special Characters not allowed")]
[Display(Name = "Description")]

Thanks

Sachin Singh · Answer

see, software world follows the separation of concern and lose coupling principles, which means no two logic depends on each other, if you won't create two separate class, then the attributes of Id and attributes of Description will bound to come together. see this in a broad range, where multiple projects use the common library, then there might be situations where a class will have Id but no description and vice versa. So, better is to use a class library project named commonAttributes and create multiple attributes (classes) for different properties, so that you can reuse them on any of your projects in the future as well, by just adding the reference.

Sachin Singh · Answer

you can create a custom attribute for description inheriting from all the attributes as public class DescriptionAttribute : ValidationAttribute { public override bool IsValid(object value) { if ( new RegularExpressionAttribute(@ "^[a-zA-Z][a-zA-Z ]+$" ) { ErrorMessage = "Special Characters not allowed" }.IsValid(value) && new RequiredAttribute { ErrorMessage = "Description can not be blank." }.IsValid(value) && new StringLengthAttribute(25) { ErrorMessage = "Max length should be less than or equal to 25." }.IsValid(value) && new DataTypeAttribute(DataType.Text).IsValid(value) ) { return true ; } else { return false ; } } } now you can use this attribute throughout the project public class anyClass { [Description] public string Name{get;set;} } Namespaces used:- using System.ComponentModel.DataAnnotations; using System.ComponentModel.DataAnnotations.Schema;

Sachin Singh · Answer

In object-oriented programing reusability means class and object, if you don't want to create class also, then you have no other options. for two classes having the same properties, you can use a metadata attribute that will inherit all the attributes for you. here, the Customer class will have all the data annotations of the Location class. [MetadataTypeAttribute( typeof( Location) )] public partial class Customer { // here customer properties }

Ramco Ramco · Answer

Hi Sachin Below i have 2 Data Annotations for 2 separate fields Id & Description. I want only 1 class for both , Methods should be different. . Is it possible [Key] [Required(ErrorMessage = "Id can not be blank.")] [StringLength(4, ErrorMessage = "Max length should be less than or equal to 4.")] [RegularExpression(@"^[a-zA-Z][a-zA-Z ]+$", ErrorMessage = "Special Characters not allowed")] [Remote("IsExist", "Location", ErrorMessage = "Id already exists")] [Display(Name = "Id")] public string Id { get; set; } [DataType(DataType.Text)] [Required(ErrorMessage = "Description can not be blank.")] [StringLength(25, ErrorMessage = "Max length should be less than or equal to 25.")] [RegularExpression(@"^[a-zA-Z][a-zA-Z ]+$", ErrorMessage = "Special Characters not allowed")] [Display(Name = "Description")] public string Description { get; set; } Thanks

Ramco Ramco · Answer

Hi Sachin This is one case . Suppose i want for another Annotation & i want to use same class. I don't want to create new class. Thanks