My task is to change the ErrorMessage property of the DataAnnotation validation attribute in MVC2.0. For example I should be able to pass an ID instead of the actual error message for the Model property and use that ID to retrieve some content(error message) from a another service e.g database, and display that error message in the View instead of the ID. In order to do this I need to set the DataAnnotation validation attribute’s ErrorMessage property.
[StringLength(2, ErrorMessage = "EmailContentID.")]
[DataType(DataType.EmailAddress)]
public string Email { get; set; }
It seems like an easy task by just overriding the DataAnnotationsModelValidatorProvider ‘s
protected override IEnumerable GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable attributes)
However it seems to be a complicated enough.
a. MVC DatannotationsModelValidator’s ErrorMessage property is read only. So I cannot set anything here
b. System.ComponentModel.DataAnnotationErrorMessage property(get and set) which is already set in MVC DatannotationsModelValidator so we cannot set again. If you try to set you get “The property cannot set more than once…” error message appears.
public class CustomDataAnnotationProvider : DataAnnotationsModelValidatorProvider
{
protected override IEnumerable<ModelValidator> GetValidators(ModelMetadata metadata, ControllerContext context, IEnumerable<Attribute> attributes)
{
IEnumerable<ModelValidator> validators = base.GetValidators(metadata, context, attributes);
foreach (ValidationAttribute validator in validators.OfType<ValidationAttribute>())
{
messageId = validator.ErrorMessage;
validator.ErrorMessage = "Error string from DB And" + messageId ;
}
//......
}
}
Can anyone please help me on this?
Here is the question: What is your motivation to changing the error message property?
Think this through very carefully, as you are heading down a path where you are obfuscating what is actually happening in the application. Certainly the database informatino is useful, but it is not really part of the validation, nor should it be.
When you head in this direction, you are essentially saying that the validation can only be invalid if there is a database problem. I see two issues with this:
It breaks the separation of concerns. You are reporting a persistance error in the model, which is not where it occurred.
The solution is not unit testable, as you must engage the database.
I don't like either of the two above.
Can you solve this? Possibly if you will create your own custom validation attribute. I would have to check and ensure that is correct. Another option is to aim for custom validation:
http://haacked.com/archive/2009/11/19/aspnetmvc2-custom-validation.aspx
This article can also help you head in the direction you desire:
http://ryanrivest.com/blog/archive/2010/01/15/reusable-validation-error-message-resource-strings-for-dataannotations.aspx
Do you want to solve this? Not really if you are attempting to keep a proper separation of concerns in your application. I would not polute my validation error message (this is not valid) with a database error (I am not valid, but the database also blew up). Just my two cents.
There are built in ways to get the error message via a resource. Instead of a database lookup to get a resource at runtime, generate resources from your database and use that for your error messages.
You can then use the ErrorMessageResourceName and ErrorMessageResourceType to allow the DataAnnotation to perform a resource lookup instead of hard-coding a specific string.
public sealed class MyModel
{
[Required(
ErrorMessageResourceName="MyDescriptionResource",
ErrorMessageResourceType=typeof(MyCustomResource))]
public string Description { get; set; }
}
Also you may want to have a look at ValidationAttribute.FormatErrorMessage Method on msdn.
This method formats an error message
by using the ErrorMessageString
property. This method appends the name
of the data field that triggered the
error to the formatted error message.
You can customize how the error
message is formatted by creating a
derived class that overrides this
method.
A quick sample (and not meant to be a definitive example)
[AttributeUsage(AttributeTargets.Property, AllowMultiple = false,
Inherited = true)]
public sealed class PostCodeValidationAttribute
: ValidationAttribute
{
public override bool IsValid(object value)
{
if( value == null )
return true;
string postCode = value as string;
if( string.IsNullOrEmpty(postCode) )
return true;
if ( !PostCode.IsValidPostCode(postCode, this.PostCodeStyle) )
return false;
return true;
}
public PostCodeStyle PostCodeStyle { get; set; }
public override string FormatErrorMessage(string name)
{
return string.Format(
"{0} is not a valid postcode for {1}", name, PostCodeStyle);
}
}
* I've omitted the PostCodeStyle enumeration as well as the PostCode class for validating a postcode.
Related
NHibernate can be extended with new implementations of IUserType, so I can customize how a mapped property is read and stored to/from the database.
An example. If I want DB null varchar to load as "n/a" string, and "n/a" string to be stored as null.
How is this possible with EF 6.2?
I am looking for a solution that doesn't break the change-tracker.
As of EF 6.2, there is no such functionality provided out of the box by the library.
If you decide to move to EF Core instead, there you can use the HasConversion functionality.
However, in your case you still wouldn't be able to use it, because there is one caveat: it can't be used to convert null values. Null always gets converted to null. From docs:
A null value will never be passed to a value converter. A null in a database column is always a null in the entity instance, and vice-versa. This makes the implementation of conversions easier and allows them to be shared amongst nullable and non-nullable properties. See GitHub issue #13850 for more information.
In that case, I suggest that instead of a Value Conversion you configure your string property to have a Backing Field. Then, you can read/write to/from the private backing field, and then have a public property handling the null value.
public class Blog
{
private string _stringFromDb;
public string MyString { get; set; }
[BackingField(nameof(_stringFromDb))]
public string MyString
{
get { return _stringFromDb ?? "n/a"; }
}
public void SetMyString(string myString)
{
// put your validation code here
_stringFromDb = myString;
}
}
In EF 6.2 the closest you could have, as a workaround, is a [NotMapped] property that can be in charge of translating the property you load from the DB.
public string StringDB { get; set; }
[NotMapped]
public string StringConverted
{
get { return MyStringProperty ?? "n/a"; }
set { MyStringProperty = value }
}
If, in addition to this, you want to hide the property being mapped to your DB by making it private, it's not as straightforward as with EF Core's backing field, but you could follow this other answer for instructions on how to achieve it.
I'm looking for a way to intercept Entity Framework's lazy load proxy implementation, or otherwise control what is returned when accessing a Navigation property that may have no value in the database.
An example of what I'm looking for is this Contact class with mailing address, business phone, etc. that may or may not have a contact person.
public partial class Contact
{
private Nullable<System.Guid> _personId;
public Nullable<System.Guid> PersonId
{
get { return _personId; }
set { SetProperty(ref _personId, value); }
}
public virtual Person Person{ get; set; }
// mailing address, other properties...
}
public partial class Person
{
private string _firstName;
public string FirstName
{
get { return _firstName; }
set { SetProperty(ref _firstName, value); }
}
private string _lastName;
public string LastName
{
get { return _lastName;}
set { SetProperty(ref _lastName;value); }
}
}
It is very useful in ASP.net Razor pages, WPF or ad-hoc reporting tools, to be able to use expressions like:
Contact c = repo.GetContact(id);
Console.WriteLine("Contact Person " + c.Person.FirstName);
Which of course fails if there is no PersonId, and hence contact.Person is null.
Tools like Ideablade Devforce have a mechanism to return a "NullEntity" for Person in this case, which allows the WriteLine to succeed. Additionally, the NullEntity for Person can be configured to have a sensible value for FirstName, like "NA".
Is there some way to override the Dynamic Proxy mechanism in EF, or otherwise intercept the reference to Person from Contact to enable this scenario?
I have investigated IDbCommandInterceptor, but that does not seem to intercept virtual navigation to individual entity properties, only navigation to entity collections.
Update _____________________________________
To elaborate on my original question, I can't modify the expression by introducing null conditional operators into the them, as these expressions are incorporated into WPF, ASP.Net Razor binding expressions, and/or report data fields, created by other developers or authors. Also, there may be multiple layers of null properties to deal with, e.g. Contact.Person.Spouse.FirstName, where either Person and/or Spouse might be a "null" property. The Devforce Ideablade implementation deals with this perfectly, but is unfortunately not an option on my current project.
you can use a null-conditional operator from c# like this
c.Person?.FirstName
This means that when Person == null , return null or otherwise return FirstName. You would still need to handle the null value
See : https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/member-access-operators#null-conditional-operators--and-
I'm having an issue trying to convert an object to json. The error is a Newtonsoft.Json.JsonSerializationException:
Self referencing loop detected for property 'Project' with type 'System.Data.Entity.DynamicProxies.Project_F29F70EF89942F6344C5B0A3A7910EF55268857CD0ECC4A484776B2F4394EF79'. Path '[0].Categories[0]'.
The problem is that the object (it's actually a list of objects) has a property which is another object that refers back to the first object:
public partial class Project
{
...
public virtual ICollection<Category> Categories { get; set; }
...
}
public partial class Category
{
...
public virtual Project Project { get; set; }
...
}
This is all fine and dandy as far as Entity Framework is concerned, but to convert this to json would result in an infinite regress, hence the exception.
Here is my code:
public async Task<HttpResponseMessage> GetProjects()
{
var projects = _projectService.GetProjects().ToList();
string jsonString = JsonConvert.SerializeObject(projects); // <-- Offending line
return Request.CreateResponse(HttpStatusCode.OK, jsonString);
}
I've looked online for solutions to this and I found this stackoverflow post:
JSON.NET Error Self referencing loop detected for type
They suggest three solutions, none of which work:
1) Ignore the circular reference:
public async Task<HttpResponseMessage> GetProjects()
{
var projects = _projectService.GetProjects().ToList();
JsonSerializerSettings settings = new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Ignore
};
string jsonString = JsonConvert.SerializeObject(projects, settings);
return Request.CreateResponse(HttpStatusCode.OK, jsonString);
}
This resulted in the call to SerializeObject(...) hanging for a bit then throwing a System.OutOfMemoryException (which tells me the circular references were NOT being ignored).
Mind you, the author of this proposed solution at stackoverflow says to set the ignore setting in WebApiConfig.cs but I tried that and it has no effect.
He also says:
"If you want to use this fix in a non-api ASP.NET project, you can add the above line to Global.asax.cs, but first add: var config = GlobalConfiguration.Configuration;"
Mine's a web API with no global file so I shouldn't have to do this.
I also don't want to ignore circular references because I don't want to lose data.
2) Preserve the circular reference:
public async Task<HttpResponseMessage> GetProjects()
{
var projects = _projectService.GetProjects().ToList();
JsonSerializerSettings settings = new JsonSerializerSettings()
{
ReferenceLoopHandling = ReferenceLoopHandling.Serialize,
PreserveReferencesHandling = PreserveReferencesHandling.Objects
};
string jsonString = JsonConvert.SerializeObject(projects, settings);
return Request.CreateResponse(HttpStatusCode.OK, jsonString);
}
This just resulted in the request timing out because it would just hang.
Again, the author says to put this in WebApiConfig.cs, but again this had no effect.
3) Add ignore/preserve reference attributes to the objects and properties:
Ignoring Categories:
public partial class Project
{
...
[JsonIgnore]
public virtual ICollection<Category> Categories { get; set; }
...
}
This has no effect. I hover over the project list and see that it still has categories, and each category still has an instance of the project. I still get the same exception.
Again, even if this worked, I don't want to ignore the categories.
Preserve Categories:
[JsonObject(IsReference = true)]
public partial class Project
{
...
public virtual ICollection<Category> Categories { get; set; }
...
}
Again, same results.
Even if this method worked, the attributes wouldn't be preserved. I'd be doing it on Entity Framework classes which are re-generated automatically every time I recompile. (Is there a way to tell it to set these attributes in the model? Can I set them on the other half of the partial class?)
Alternatively, I'm open to suggestions other than converting to json and sending back in the response. Is there another way to get the data back to the client?
What would be the fix to this problem? Thanks.
Briefly
The best way to fix this problem is to create completely brand-new Models (xxxModel, xxxViewModel, xxxResponse, etc..) on Presentation layer which will be returned to end-users. Than just cast one object to another using AutoMapper or your own custom methods.
Keep your database entities separate from real world!
In detail
There are so many problems that you will encounter:
Disclosure of sensitive data. Your database entity could/will contain sensitive data which end-users shouldn't receive;
Performance issues and waste of RAM and CPU. It would be better to load only those properties that end-users is required, instead all;
Serialization problems. EF entities almost always contain Navigation properties which will be serialized together in case lazy-loading enabled. Imagine dozens related entities, which will be lazy-loaded when your composite root is being serialized. It will cause dozens unexpected requests to database;
Fragility. Any changes related your EF entities will affect on Presentation Layer and on end-users. For instance, in case with API, new added property just extend response, but deleted or renamed will break logic in your customers' application.
There are a lot of other problems, just be careful.
I would recommend not Serializing Entity Framework classes and creating a specific class that only inherits from Object and has only the data you need
In my MVC application I have a requirement where I want user to insert Unique value in a column.
i.e.: Username should be unique in Users table.
I used [Indes(IsUnique = true)] data annotation in my model.
But when I insert duplicate value in the field it throws an exception, but I want to display an Error Message on my View saying Please try with a different Username
Please help me what should I do here?
You can use one of those:
Write your CustomValidator (ny recommendation)
[CustomRemoteValidator(ErrorMessage = #"Username already in use")]
public string Username{ get; set; }`
And override IsValid method
public override bool IsValid(object value)
{
return !(this.DbContext.Set<User>().Any(a =>
a.Username.Equals((string)value));
}
Check it in your business layer.
Check it before save entity in database by overriding SaveChanges() method.
I have following property in my Model Metadata class:
[Required(ErrorMessage = "Spent On is required")]
[RegularExpression(#"[0-1][0-9]/[0-3][0-9]/20[12][0-9]",
ErrorMessage = "Please enter date in mm/dd/yyyy format")]
[DataType(DataType.Date)]
[DisplayName("Spent On")]
public DateTime SpentOn { get; set; }
But whenever I call ModelState.IsValid it always returns false because regex is not validating. I have matched the entered date (08/29/2010) against new regex using same pattern and it matches perfectly.
What am I doing wrong?
Actualy there is another workaround for this. You can simply subclass the RegularExpressionAttribute
public class DateFormatValidatorAttribute : RegularExpressionAttribute {
public DateFormatValidatorAttribute()
: base(#"[0-1][0-9]/[0-3][0-9]/20[12][0-9]")
{
ErrorMessage = "Please enter date in mm/dd/yyyy format";
}
public override bool IsValid(object value) {
return true;
}
}
in your Global.asax.cs on application start register the RegularExpression addapter for client side validation like so:
DataAnnotationsModelValidatorProvider.RegisterAdapter(
typeof(DateFormatValidatorAttribute),
typeof(RegularExpressionAttributeAdapter));
Now you get to have the build-in MVC regular exression validator client side and keep the DateTime as your property type
That's because regex applies to strings and not DateTime properties. If the user enters an invalid string which cannot be parsed to a DateTime instance from the model binder it will add a generic error message before your regex pattern executes.
You have a couple of possibilities:
Customize the error message in a resource file
Write a custom model binder
Use a string property (I feel guilty for proposing this :-))