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• ASP.NET MVC 2 validation using DTOs instead of domain entities

  - by Kevin Pang

  I'm struggling to mesh two best practices together: Using DataAnnotations + ModelBinding for validation in ASP.NET MVC 2 Using DTOs instead of domain entities when passing data via the ViewModel If I want to pass over DTOs instead of domain entities, then leveraging DataAnnotations + ModelBinding for validation would require me to specify validation attributes on my DTO classes. This results in a lot of duplicated work since multiple DTOs may hold overlapping fields with the same validation restrictions. This means that any time I change a validation rule in my domain, I have to go find all DTOs that correspond with that value and update their validation attributes.

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• WPF Validation with ContentPresenter

  - by Chris

  Hi, I have a WPF user control which needs to validate some fields. It is bound to a class implementing IDataErrorInfo. When I set the user control as the content of my ContentPresenter in another, already open, window, I can see validation occurring, and error messages being returned, however, I don't get any validation adorner - e.g. the default red outline. If I enter the field and leave it (triggering re-validation) the validation adorner appears. Also, if I show the user control in it's own window it shows the validation adorner immediately. (I'm using Caliburn IResults to do this underneath, e.g. Show.Dialog<VM>(); but I suspect this isn't related) Can anyone offer any suggestion why the validation adorners aren't appearing immediately. (I had guessed animation on my ContentPresenter ContentChanged, however, I have removed this and still experience the problem. thanks, Chris

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• Is there a way to validates_presence_of only one time? (to skip that validation once the user's been

  - by GoodGets

  So, I'd like for a user to see an error message if he submits a comment and the :name is blank (typical error message, don't need help with that). However, I'd then like to allow the user to skip that validation once he's been notified that "we like all comments to have a name." So, he submits the comment once, sees the notification, then can submit the form again unchanged if he really doesn't want to add a name, and the validates_presences_of :name is skipped. But, I'm not sure how to go about doing this. I thought about checking to see where the request is coming from, but after a create, errors are handed off to the "new" action, which is the same as actual "new" comments. I then thought about checking to see if flash[errors] were present, but that won't work because there are other validations a comment has to pass. Finally, I thought about trying a validates_presences_of :name, :unless = :notified but wasn't sure how to define notified. I honestly hate asking such an open ended question, but wasn't sure where to get started. So, is there a way to just check a certain validation once?

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• Data validation best practices: how can I better construct user feedback?

  - by Cory Larson

  Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. I've migrated this question from StackOverflow where I originally asked it with little response. Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interested in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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• Data validation best practices: how can I better construct user feedback?

  - by Cory Larson

  Data validation, whether it be domain object, form, or any other type of input validation, could theoretically be part of any development effort, no matter its size or complexity. I sometimes find myself writing informational or error messages that might seem harsh or demanding to unsuspecting users, and frankly I feel like there must be a better way to describe the validation problem to the user. I know that this topic is subjective and argumentative. StackOverflow might not be the proper channel for diving into this subject, but like I've mentioned, we all run into this at some point or another. There are so many StackExchange sites now; if there is a better one, feel free to share! Basically, I'm looking for good resources on data validation and user feedback that results from it at a theoretical level. Topics and questions I'm interested in are: Content Should I be describing what the user did correctly or incorrectly, or simply what was expected? How much detail can the user read before they get annoyed? (e.g. Is "Username cannot exceed 20 characters." enough, or should it be described more fully, such as "The username cannot be empty, and must be at least 6 characters but cannot exceed 30 characters."?) Grammar How do I decide between phrases like "must not," "may not," or "cannot"? Delivery This can depend on the project, but how should the information be delivered to the user? Should it be obtrusive (e.g. JavaScript alerts) or friendly? Should they be displayed prominently? Immediately (i.e. without confirmation steps, etc.)? Logging Do you bother logging validation errors? Internationalization Some cultures prefer or better understand directness over subtlety and vice-versa (e.g. "Don't do that!" vs. "Please check what you've done."). How do I cater to the majority of users? I may edit this list as I think more about the topic, but I'm genuinely interest in proper user feedback techniques. I'm looking for things like research results, poll results, etc. I've developed and refined my own techniques over the years that users seem to be okay with, but I work in an environment where the users prefer to adapt to what you give them over speaking up about things they don't like. I'm interested in hearing your experiences in addition to any resources to which you may be able to point me.

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• Domain Validation in a CQRS architecture

  - by Jupaol

  Basically I want to know if there is a better way to validate my domain entities. This is how I am planning to do it but I would like your opinion The first approach I considered was: class Customer : EntityBase<Customer> { public void ChangeEmail(string email) { if(string.IsNullOrWhitespace(email)) throw new DomainException(“...”); if(!email.IsEmail()) throw new DomainException(); if(email.Contains(“@mailinator.com”)) throw new DomainException(); } } I actually do not like this validation because even when I am encapsulating the validation logic in the correct entity, this is violating the Open/Close principle (Open for extension but Close for modification) and I have found that violating this principle, code maintenance becomes a real pain when the application grows up in complexity. Why? Because domain rules change more often than we would like to admit, and if the rules are hidden and embedded in an entity like this, they are hard to test, hard to read, hard to maintain but the real reason why I do not like this approach is: if the validation rules change, I have to come and edit my domain entity. This has been a really simple example but in RL the validation could be more complex So following the philosophy of Udi Dahan, making roles explicit, and the recommendation from Eric Evans in the blue book, the next try was to implement the specification pattern, something like this class EmailDomainIsAllowedSpecification : IDomainSpecification<Customer> { private INotAllowedEmailDomainsResolver invalidEmailDomainsResolver; public bool IsSatisfiedBy(Customer customer) { return !this.invalidEmailDomainsResolver.GetInvalidEmailDomains().Contains(customer.Email); } } But then I realize that in order to follow this approach I had to mutate my entities first in order to pass the value being valdiated, in this case the email, but mutating them would cause my domain events being fired which I wouldn’t like to happen until the new email is valid So after considering these approaches, I came out with this one, since I am going to implement a CQRS architecture: class EmailDomainIsAllowedValidator : IDomainInvariantValidator<Customer, ChangeEmailCommand> { public void IsValid(Customer entity, ChangeEmailCommand command) { if(!command.Email.HasValidDomain()) throw new DomainException(“...”); } } Well that’s the main idea, the entity is passed to the validator in case we need some value from the entity to perform the validation, the command contains the data coming from the user and since the validators are considered injectable objects they could have external dependencies injected if the validation requires it. Now the dilemma, I am happy with a design like this because my validation is encapsulated in individual objects which brings many advantages: easy unit test, easy to maintain, domain invariants are explicitly expressed using the Ubiquitous Language, easy to extend, validation logic is centralized and validators can be used together to enforce complex domain rules. And even when I know I am placing the validation of my entities outside of them (You could argue a code smell - Anemic Domain) but I think the trade-off is acceptable But there is one thing that I have not figured out how to implement it in a clean way. How should I use this components... Since they will be injected, they won’t fit naturally inside my domain entities, so basically I see two options: Pass the validators to each method of my entity Validate my objects externally (from the command handler) I am not happy with the option 1 so I would explain how I would do it with the option 2 class ChangeEmailCommandHandler : ICommandHandler<ChangeEmailCommand> { public void Execute(ChangeEmailCommand command) { private IEnumerable<IDomainInvariantValidator> validators; // here I would get the validators required for this command injected, and in here I would validate them, something like this using (var t = this.unitOfWork.BeginTransaction()) { var customer = this.unitOfWork.Get<Customer>(command.CustomerId); this.validators.ForEach(x =. x.IsValid(customer, command)); // here I know the command is valid // the call to ChangeEmail will fire domain events as needed customer.ChangeEmail(command.Email); t.Commit(); } } } Well this is it. Can you give me your thoughts about this or share your experiences with Domain entities validation EDIT I think it is not clear from my question, but the real problem is: Hiding the domain rules has serious implications in the future maintainability of the application, and also domain rules change often during the life-cycle of the app. Hence implementing them with this in mind would let us extend them easily. Now imagine in the future a rules engine is implemented, if the rules are encapsulated outside of the domain entities, this change would be easier to implement

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• asp.net mvc client side validation; manually calling validation via javascript for ajax posts

  - by Jopache

  Under the built in client side validation (Microsoft mvc validation in mvc 2) using data annotations, when you try to submit a form and the fields are invalid, you will get the red validation summary next to the fields and the form will not post. However, I am using jquery form plugin to intercept the submit action on that form and doing the post via ajax. This is causing it to ignore validation; the red text shows up; but the form posts anyways. Is there an easy way to manually call the validation via javascript when I'm submitting the form? I am still kind of a javascript n00b. I tried googling it with no results and looking through the js source code makes my head hurt trying to figure it out. Or would you all recommend that I look in to some other validation framework? I liked the idea of jquery validate; but would like to define my validation requirements only in my viewmodel. Any experiences with xval or anything of the sort?

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• Is it practical to have perfect validation score on HTML?

  - by Truth

  I was in a heated discussion the other day, about whether or not it's practical to have a perfect validation score on any HTML document. By practical I mean: Does not take a ridiculous amount of time compared to it's almost-perfect counterpart. Can be made to look good on older browsers and to be usable on very old browsers. Justifies the effort it may take to do so (does it come with some kind of reward on SEO/Usability/Accessibility that cannot be achieved in a simpler way with almost-perfect validation) So basically, is perfect validation score practical on any HTML document?

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• Spring Batch validation

  - by sergionni

  Hello. Does Spring Batch framework provide its specific validation mechanism? I mean, how it's possible to specify validation bean? My validation is result of @NamedQuery - if query returned result, the validation is OK, else - false.

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• jquery validation plugin - different treatment for display errors vs. clearing errors

  - by RyOnLife

  I am using the popular jQuery Validation Plugin. It's very flexible with regards to when validations are run (onsubmit, onfocusout, onkeyup, etc.). When validations do run, as appropriate, errors are both displayed and cleared. Without hacking the plugin core, I'd like a way to split the behavior so: Errors are only displayed onsubmit But if the user subsequently enters a valid response, errors are cleared onsubmit, onfocusout, etc. Just trying to create a better user experience: Only yell at them when they submit, yet still get the errors out of their face as soon as possible. When I ran through the options, I didn't see the callbacks necessary to accomplish this. I'd like to make it work without having to hack the plugin core. Anyone have some insights? Thanks.

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• How to provide warnings during validation in ASP.NET MVC?

  - by Alex

  Sometimes user input is not strictly invalid but can be considered problematic. For example: A user enters a long sentence in a single-line Name field. He probably should have used the Description field instead. A user enters a Name that is very similar to that of an existing entity. Perhaps he's inputting the same entity but didn't realize it already exists, or some concurrent user has just entered it. Some of these can easily be checked client-side, some require server-side checks. What's the best way, perhaps something similar to DataAnnotations validation, to provide warnings to the user in such cases? The key here is that the user has to be able to override the warning and still submit the form (or re-submit the form, depending on the implementation). The most viable solution that comes to mind is to create some attribute, similar to a CustomValidationAttribute, that may make an AJAX call and would display some warning text but doesn't affect the ModelState. The intended usage is this: [WarningOnFieldLength(MaxLength = 150)] [WarningOnPossibleDuplicate()] public string Name { get; set; } In the view: @Html.EditorFor(model => model.Name) @Html.WarningMessageFor(model => model.Name) @Html.ValidationMessageFor(model => model.Name) So, any ideas?

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• MVC2 jQuery Validation & Custom Business Objects

  - by durilai

  I have an application that was built with MVC1 and am in the process of updating to MVC2. I have a custom DLL and BLL, of which the model objects are custom business objects that reside in a separate class library. I was using this validation library in MVC1, which worked great. It worked great, but I want to eliminate the extra plugins and use what is available. Rather than use the Enterprise Library validation attributes I have converted to using DataAnnotations and want to use jQuery validation as the client side validation. My questions are: 1) Is the MicrosoftMvcJQueryValidation JS file still required, where do I download. 2) How to you automate the validation to views that do not have models, IE Membership sign in page? 3) How to you add model errors in a custom business layer. Thanks for any help or guidance.

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• Force validation on bound controls in WPF

  - by Valentin Vasilyev

  Hello. I have a WPF dialog with a couple of textboxes on it. Textboxes are bound to my business object and have WPF validation rules attached. The problem is that user can perfectly click 'OK' button and close the dialog, without actually entering the data into textboxes. Validation rules never fire, since user didn't even attempt entering the information into textboxes. Is it possible to force validation checks and determine if some validation rules are broken? I would be able to do it when user tries to close the dialog and prohibit him from doing it if any validation rules are broken. Thank you.

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• Simple ASP.Net MVC 1.0 Validation

  - by Mike

  On the current project we are working on we haven't upgraded to MVC 2.0 yet so I'm working on implementing some simple validation with the tools available in 1.0. I'm looking for feedback on the way I'm doing this. I have a model that represents a user profile. Inside that model I have a method that will validate all the fields and such. What I want to do is pass a controller to the validation method so that the model can set the model validation property in the controller. The goal is to get the validation from the controller into the model. Here is a quick example public FooController : Controller { public ActionResult Edit(User user) { user.ValidateModel(this); if (ModelState.IsValid) ....... ....... } } And my model validation signature is like public void ValidateModel(Controller currentState) What issues can you see with this? Am I way out to lunch on how I want to do this?

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• How to combine mvc2 client side validation with other client side validation?

  - by Andrey

  I have a page using mvc2 with client side validation. The client side validation is provided by Microsoft Ajax mvc validation script. This does very well to validate all fields that are related to the model. I also have fields that are never sent to the server such as the confirm password value, and the accept agreement. For these fields i need pure client side validation. I created the javascript to do this, but am now having a hard time integrating the two validatiosn together. I was hoping that i could do something like add another error to an array, or set the page manually to not valid to make sure that the user cannot submit. Basically follow the same approach that i would with normal asp.net validation. I can't find anything like that. In all examples validators are discussed that are connected to parts of the model. What is my best approach here?

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• Excel validation range limits

  - by richardtallent

  When Excel saves a file, it attempts to combine identical Validation settings into a single rule with multiple ranges. This creates one of three issues, depending on the file type you choose to save: When saving as a standard Excel file (Office 2000 BIFF), a maximum of 1024 non-contiguous ranges that can have the same validation setting. When saving as a SpreadsheetML (Office 2002/2003 XML) file, you are limited to the number of non-contiguous ranges that can be represented, comma-delimited in R1C1 format, in 1024 characters. When saving as an Open Office XML (Office 2007 *.xlsx), there is a maximum of 511 non-contiguous ranges that can have the same validation setting. (I don't have Office 2007, I'm using the file converter for Office 2003). Once you bust any of these limits, the remaining ranges with the same Validation settings have their Validation settings wiped. For (1) and (3), Excel warns you that it can't save all of the formatting, but for (2) it does not.

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• ASP.NET validation controls

  - by mehmet6parmak

  Hi All, I want to use Validation Controls but I dont want them to show their Error Messages when invalid data exist. Instead I'm going to iterate through the validation controls and show error messages inside my little ErrorMessage Control for (int i = 0; i < Page.Validators.Count; i++) { if (!Page.Validators[i].IsValid) { divAlert.InnerText = Page.Validators[i].ErrorMessage; return false; } } I'm doing this because i have little space to show the error message. You can ask why are you using validation control if you dont want to show them My asnwer is "I use them for validation logic they handle" I looked the properties of the validation controls and cant find something that wil help me doing this. Any Idea? Thanks

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• NET Framework Validation Library

  - by Kane

  As I see it most applications have a requirement for some form of validation and a number of fantastic free offerings are available (I.E., Fluent Validation, Validation Block, Spring, Castle Windsor, etc). My question is why does the .NET Framework not include any inbuilt validation libraries? I am aware the .NET Framework allows a developer the ability to build their own validation libraries/methods/etc. and anything provided as part of the .NET Framework would not always meet everyone’s needs. But surely something could have been included? ASP.NET has a minimal set of validators but these have not really been extended since .NET 2.0 was released.

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• C# UserControl Validation

  - by Barry

  Hi, I have a UserControl with a Tab Control containing three tabs. Within the tabs are multiple controls - Datetimepickers, textboxes, comboboxes. There is also a Save button which when clicked, calls this.ValidateChildren(ValidationConstraints.Enabled) Now, I click save and a geniune validation error occurs. I correct the error and then click save again - valdiation errors occur on comboboxes on a different tab. If I navigate to this tab and click save, everything works fine. How can this be? I haven't changed any values in the comboboxes so how can the fail validation then pass validation? The comboboxes are bound to a dataset with their selectedValue and Text set. I just don't understand what is happening here. This behaviour also occurs for some textboxes too. The validation rule is that they have to be a decimal - the default value is zero, which is allowed. The same thing happens, they fail validation the first time - I make no changes, click save again and they pass validation. If you need any further information please let me know thanks Barry

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• Custom model validation of dependent properties using Data Annotations

  - by Darin Dimitrov

  Since now I've used the excellent FluentValidation library to validate my model classes. In web applications I use it in conjunction with the jquery.validate plugin to perform client side validation as well. One drawback is that much of the validation logic is repeated on the client side and is no longer centralized at a single place. For this reason I'm looking for an alternative. There are many examples out there showing the usage of data annotations to perform model validation. It looks very promising. One thing I couldn't find out is how to validate a property that depends on another property value. Let's take for example the following model: public class Event { [Required] public DateTime? StartDate { get; set; } [Required] public DateTime? EndDate { get; set; } } I would like to ensure that EndDate is greater than StartDate. I could write a custom validation attribute extending ValidationAttribute in order to perform custom validation logic. Unfortunately I couldn't find a way to obtain the model instance: public class CustomValidationAttribute : ValidationAttribute { public override bool IsValid(object value) { // value represents the property value on which this attribute is applied // but how to obtain the object instance to which this property belongs? return true; } } I found that the CustomValidationAttribute seems to do the job because it has this ValidationContext property that contains the object instance being validated. Unfortunately this attribute has been added only in .NET 4.0. So my question is: can I achieve the same functionality in .NET 3.5 SP1? UPDATE: It seems that FluentValidation already supports clientside validation and metadata in ASP.NET MVC 2. Still it would be good to know though if data annotations could be used to validate dependent properties.

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• Validation in n-tier asp.net mvc applications

  - by sTodorov

  Dear Stack Overflow gurus, I am looking for some practical/theoretical information regarding best practices for validation in asp.net mvc n-tier applications. I am working on a .Net application divided into the following layers: UI - Mvc3 BLL layer - all business rules. Decoupled from data access and UI layers through interfaces DAL layer - Data access with the repository pattern, EF4 and pocos Now, I am looking for a nice, clean and transparent way to specify my validation rules. Here are some thoughts on the matter so far: UI validation should only be responsible for user input and its validity. BLL validation should be handling the validity of the data regarding the application business rules. My main concern is how to bind the BLL and UI validation in the most efficient way. One think I am would like to avoid is having the UI check in a collection of validation and adding manually errors to the ModelState. Furthermore, I do not want to pass the ModelState to the BLL to be populated in there. I will appreciate any thoughts on the matter. P.S. Should this question be marked as a discussion ?

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• pass Validation error to UI element in WPF?

  - by Tony

  I am using IDataErrorInfo to validate my data in a form in WPF. I have the validation implemented in my presenter. The actual validation is happening, but the XAML that's supposed to update the UI and set the style isn't happening. Here it is: <Style x:Key="textBoxInError" TargetType="{x:Type TextBox}"> <Style.Triggers> <Trigger Property="Validation.HasError" Value="true"> <Setter Property="ToolTip" Value="{Binding RelativeSource={x:Static RelativeSource.Self}, Path=(Validation.Errors)[0].ErrorContent}"/> <Setter Property="Background" Value="Red"/> </Trigger> </Style.Triggers> </Style> The problem is that my binding to Validation.Errors contains no data. How do I get this data from the Presenter class and pass it to this XAML so as to update the UI elements? EDIT: Textbox: <TextBox Style="{StaticResource textBoxInError}" Name="txtAge" Height="23" Grid.Row="3" Grid.Column="0" HorizontalAlignment="Right" VerticalAlignment="Center" Width="150"> <TextBox.Text> <Binding Path="StrAge" Mode="TwoWay" ValidatesOnDataErrors="True" UpdateSourceTrigger="PropertyChanged"/> </TextBox.Text> The validation occurs, but the style to be applied when data is invalid is not happening.

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• How do you reenable a validation control w/o it simultaneously performing an immediate validation?

  - by Velika2

  When I called this function to enable a validator from client javascript: `ValidatorEnable(document.getElementById('<%=valPassportOtherText.ClientID%>'), true); //enable` validation control the required validation control immediately performed it validation, found the value in the associated text box blank and set focus to the textbox (because SetFocusOnError was set to true). As a result, the side effect was that focus was shifted to the control that was associated with the Validation control, i teh example, txtSpecifyOccupation. <asp:TextBox ID="txtSpecifyOccupation" runat="server" AutoCompleteType="Disabled" CssClass="DefaultTextBox DefaultWidth" MaxLength="24" Rows="2"></asp:TextBox> <asp:RequiredFieldValidator ID="valSpecifyOccupation" runat="server" ControlToValidate="txtSpecifyOccupation" ErrorMessage="1.14b Please specify your &lt;b&gt;Occupation&lt;/b&gt;" SetFocusOnError="True">&nbsp;Required</asp:RequiredFieldValidator> Perhaps there is a way to enable the (required) validator without having it simultaneously perform the validation (at least until the user has tabbed off of it?) I'd like validation of the txtSpecifyOccupation textbox to occur only on a Page submit or when the user has tabbed of the required txtSpecifyoccupation textbox. How can I achieve this?

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• How do you reenable a validation control w/o it simultaneously perform an immediate validation?

  - by Velika2

  When I called this function to enable a validator from client javascript: `ValidatorEnable(document.getElementById('<%=valPassportOtherText.ClientID%>'), true); //enable` validation control the required validation control immediately performed it validation, found the value in the associated text box blank and set focus to the textbox (because SetFocusOnError was set to true). As a result, the side effect was that focus was shifted to the control that was associated with the Validation control, i teh example, txtSpecifyOccupation. <asp:TextBox ID="txtSpecifyOccupation" runat="server" AutoCompleteType="Disabled" CssClass="DefaultTextBox DefaultWidth" MaxLength="24" Rows="2"></asp:TextBox> <asp:RequiredFieldValidator ID="valSpecifyOccupation" runat="server" ControlToValidate="txtSpecifyOccupation" ErrorMessage="1.14b Please specify your &lt;b&gt;Occupation&lt;/b&gt;" SetFocusOnError="True">&nbsp;Required</asp:RequiredFieldValidator> Perhaps there is a way to enable the (required) validator without having it simultaneously perform the validation (at least until the user has tabbed off of it?) I'd like validation of the txtSpecifyOccupation textbox to occur only on a Page submit or when the user has tabbed of the required txtSpecifyoccupation textbox. How can I achieve this?

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• Custom model validation of dependent properties using Data Annotations

  - by Darin Dimitrov

  Since now I've used the excellent FluentValidation library to validate my model classes. In web applications I use it in conjunction with the jquery.validate plugin to perform client side validation as well. One drawback is that much of the validation logic is repeated on the client side and is no longer centralized at a single place. For this reason I'm looking for an alternative. There are many examples out there showing the usage of data annotations to perform model validation. It looks very promising. One thing I couldn't find out is how to validate a property that depends on another property value. Let's take for example the following model: public class Event { [Required] public DateTime? StartDate { get; set; } [Required] public DateTime? EndDate { get; set; } } I would like to ensure that EndDate is greater than StartDate. I could write a custom validation attribute extending ValidationAttribute in order to perform custom validation logic. Unfortunately I couldn't find a way to obtain the model instance: public class CustomValidationAttribute : ValidationAttribute { public override bool IsValid(object value) { // value represents the property value on which this attribute is applied // but how to obtain the object instance to which this property belongs? return true; } } I found that the CustomValidationAttribute seems to do the job because it has this ValidationContext property that contains the object instance being validated. Unfortunately this attribute has been added only in .NET 4.0. So my question is: can I achieve the same functionality in .NET 3.5 SP1? UPDATE: It seems that FluentValidation already supports clientside validation and metadata in ASP.NET MVC 2. Still it would be good to know though if data annotations could be used to validate dependent properties.

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