Starting with CTP5, you can call the “GetValidationErrors()” method on the DbContext base class to retrieve a list of validation errors within the model objects you are working with. In addition to reactively handling validation exceptions, EF Code First also allows you to proactively check for validation errors. This new support means that the below code – which violates one of our above business rules – will automatically throw an exception (and abort the transaction) when we call the “SaveChanges()” method on our Northwind DbContext: You do not need to write any code to cause this to happen – this support is now enabled by default. Each ValidationResult returned can supply both an error message as well as an optional list of property names that caused the violation (which is useful when displaying error messages within UI).ĮF Code-First (starting with CTP5) now automatically invokes the Validate() method when a model object that implements the IValidatableObject interface is saved. The IValidatableObject.Validate() method can apply validation rules that span across multiple properties, and can yield back multiple validation errors. We will enforce these business rules by implementing the IValidatableObject interface on our Product class, and by implementing its Validate() method like so: New units can’t be ordered if there are already more than 100 units in stock.New units can’t be ordered if the Product is in a discontinued state.NET 4 within the namespace) to implement two custom validation rules on a Product model class. Several people have asked - “Does EF Code First also support a way to implement class-level validation methods on model objects, for validation rules than need to span multiple property values?” It does – and one easy way you can enable this is by implementing the IValidatableObject interface on your model classes.īelow is an example of using the IValidatableObject interface (which is built-into. Class-Level Model Validation using IValidatableObjectĭataAnnotation attributes provides an easy way to validate individual property values on your model classes. I showed some code samples of this in action in my previous post. This provides a really easy way to validate property values on your models. You can also create your own custom validation attributes (like this cool validator) and have them be automatically enforced by EF Code First as well. NET 4 – to your model classes in order to enforce that the model properties are valid before they are persisted to a database. You can apply validation attributes like, , and – all of which are built-into. It provides a pretty easy way to enable property-level validation logic within your model layer. Automatic support for enforcing DataAnnotation validation attributes on models was one of the improvements I discussed. In my blog post a few days ago I talked about a few of the improvements introduced with the new CTP5 build. When the validation fails, the error message is automatically shown in the TextBlock with name „labelErrors“.Earlier this week the data team released the CTP5 build of the new Entity Framework Code-First library. The BindingGroup property of the window is set to a new BindingGroup object that contains our custom validation rule as ValidationRule. The properties are bound to TextBoxes like usual. How to use model class and validation in XAML: If (string.IsNullOrEmpty(validationAttribute.ErrorMessage)) We set the error message if the validation of the property fails. If (bindingGroup.TryGetValue(item, pi.Name, out object val)) We continue if we found a data annotation First we find all properties that have attributes.įoreach (var attrib in Attribute.GetCustomAttributes(pi, true)) Public override ValidationResult Validate(object value, CultureInfo cultureInfo)īindingGroup bindingGroup = (BindingGroup)value įoreach (var item in ()) internal class GenericValidationRule : ValidationRule This uses reflection to find and check the properties. This can be used in POCO objects and is therefore fully compatible with the MVVM pattern and ORM database mapping technology like Entity Framework Code First. We will then define the validation settings on the model level and validate the user input in the view. This post shows how to combine both approaches. In WPF on the other hand, validation rules are used to validate entries made by the user and display error messages. The ASP.NET MVC for example uses Data Annotations to annotate the model classes with the definition of valid ranges, etc. NET Framework uses many different approaches for validation.
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