c#: Custom Validation Example

Validation is a big thing for any application.  I am currently working on implementing validation in my WCF layer that doesn't rely on me checking each operation and then hardcoding validation logic into a gigantic class.  I really like the way WCF does model validation, so I decided to start trying to reproduce it to figure out how they did it.

It turns out that it is pretty simple as the following code suggests.  I created a base attribute called Validation Attribute.  I created a BaseModel that has a validate method on it.  That method does some simple reflection to get all the attributes for all the properties in the given class.  It just calls IsValid on those attributes to run the specified logic. 

Check it out.

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publicclassBaseModel {     publicboolValidate()     {         var result =true;           foreach(var propertyinthis.GetType().GetProperties())         {             foreach(var attributeinproperty.GetCustomAttributes(true))             {                 if(attributeisValidationAttribute)                 {                     try                     {                         var attr = (ValidationAttribute)attribute;                         result = result && attr.IsValid(property.GetValue(this,null));                     }                     catch(Exception)                     {                         result =false;                     }                 }             }         }           returnresult;     } }

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publicclassLoginModel : BaseModel {     [UserNameValidation]     publicstringUserName {get;set; } }

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[System.AttributeUsage(System.AttributeTargets.Property)] publicclassValidationAttribute : Attribute {     publicvirtualboolIsValid(objectobj)     {         returnfalse;     } }

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publicclassUserNameValidationAttribute : ValidationAttribute {     privateconststringUSER_NAME_REGEX =@"^\w+$";       publicoverrideboolIsValid(objectobj)     {         if(obj ==null)         {             returnfalse;         }           var value = objasstring;                   if(Regex.IsMatch(value, USER_NAME_REGEX))         {             returntrue;         }           returnfalse;     } }

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classProgram {     staticvoidMain(string[] args)     {         var loginModel =newLoginModel();         loginModel.UserName ="UserName";         Console.WriteLine(loginModel.Validate());     } }