Validating domain objects and not only ... Hi little now I do not regularly written due to lack of time but has already commenced in September so time to work. Today I would like discuss the problem of validation domain objects but not only. This interface can be used in any object. I would like to achieve the objectives of which are two: First of all, the validation must be reusable and easily accessible. The second objective is the ability to validate the entire object at once and return to the controller information about all the wrong boxes.
interface IValidatable
Let's start from the beginning because the validation must be easily accessible and reusable, any object that will have validation must implement the above interface. Nothing special: Public interface
IValidatable
ValidationResult This class consists of a dictionary that stores information about the error and check that the information relates. However, because the data field can have a lot of mistakes because stores a list of strings. In addition, one has two functions for counting errors and another error to add to the dictionary. Class itself looks like this: public class
ValidationResult
{private IDictionary \u0026lt;string, IList \u0026lt;string>> _validationErrors;
public ValidationResult()
{
_validationErrors = new Dictionary<string, IList<string>>();
} public IDictionary<string, IList<string>> Errors
{
get { return _validationErrors; }
private set { _validationErrors = value; }
}
public int CountErrors()
{
int errorCount = 0;
foreach (var errorMessages in _validationErrors.Values)
{
errorCount += errorMessages.Count;
}
return errorCount;
}
public void AddError(KeyValuePair<string, string> error)
{
if (error.Key != null)
{
if (_validationErrors.ContainsKey(error.Key))
{
_validationErrors[error.Key].Add(error.Value);
}
else
{
IList<string> newErrorList = new List<string>();
newErrorList.Add(error.Value);
_validationErrors.Add(new KeyValuePair<string, IList \u0026lt;string>> (error.Key, newErrorList));}
}}}
ValidationHelper
To facilitate the addition of a little bug I decided to create a secondary class that will be somewhat automate adding errors. This will be an object which has two methods that give an error if the condition is not fulfilled. They differ only in one parameter associated with a key error. This is usually called just as the field concerned. And in the end, a version of the method of expression lambda. The other takes a string parameter. So it is more generalized. Class looks like this: public class
ValidationHelper \u0026lt;T>
{public
ValidationHelper ()
{} public KeyValuePair
\u0026lt;string, string> CreateErrorIf (bool condition, String errorKey, String errorMessageKey) {if (condition) return new KeyValuePair
\u0026lt;string, string> (errorKey, ResourceHelper.GetErrorMessage (errorMessageKey));
else return new KeyValuePair \u0026lt;string, string> ( );
}
public KeyValuePair \u0026lt;string, string> CreateErrorIf \u0026lt;TResult> (bool condition, Expression \u0026lt;Func \u0026lt;T, TResult>> errorKey, string errorMessageKey)
{var
expressionMember = errorKey.Body as MemberExpression;
CreateErrorIf return (condition, expressionMember.Member.Name, errorMessageKey);
}}
method that uses lambda expressions simply take from him the name of the field. And now an example using these classes: public class
User: BaseEntity, IEntity, IValidatable
{
...
public virtual ValidationResult Validate()
{
ValidationResult validationResult = new ValidationResult();
ValidationHelper<User> validationHelper = new ValidationHelper<User>();
validationResult.AddError(validationHelper.CreateErrorIf(!String.IsNullOrEmpty(Username), f => f.Username, ResourceKey.Common.RequiredField));
validationResult.AddError(validationHelper.CreateErrorIf(Username.Length >= 256, f => f.Username, ResourceKey.Common.FieldLength));
...
validationResult return;}
}
addition to writing this mechanism, slowly add missing tests in the project already associated with a ready functionality. That's all for today:)
