NHibernate Succinctly^®
by Ricardo Peres

CHAPTER 9

Validation

NHibernate Validator

A proper data framework allows you to validate entities against business rules and invalid values. NHibernate Validator can be used precisely for that. It is a general purpose validation framework that integrates tightly with NHibernate.

The best way to get it is through NuGet as NHibernate.Validator:

Another way to get it is by downloading it from SourceForge: http://sourceforge.net/projects/nhcontrib/files/NHibernate.Validator.

You can also get the source code from GitHub: https://github.com/darioquintana/NHibernate-Validator.

Once you have set it up, you must decide how you want to apply validation. NHibernate Validator supports configuring validation:

By attributes.
By XML.
By code.

You see, some things in the NHibernate world never change!

To use NHibernate Validator, we need to set up the framework to work together with NHibernate. This is achieved through a listener that performs validation on entities when they are about to be saved or updated. If any validation error occurs, an InvalidStateException is thrown. You can call its GetInvalidValues() to find out exactly what is wrong and fix it.

We integrate NHibernate Validator with the NHibernate Configuration instance before building any session factory. The following shows how to do it with loquacious configuration:

FluentConfiguration validatorConfiguration = new FluentConfiguration();

validatorConfiguration.SetDefaultValidatorMode(ValidatorMode.UseExternal)

.IntegrateWithNHibernate.ApplyingDDLConstraints().RegisteringListeners();

NHibernate.Validator.Cfg.Environment.SharedEngineProvider = new NHibernateSharedEngineProvider();

ValidatorEngine validatorEngine = NHibernate.Validator.Cfg.Environment.SharedEngineProvider.GetEngine();

validatorEngine.Configure(validatorConfiguration);

cfg.Initialize(validatorEngine);

Tip: Add using statements for the NHibernate.Validator.Cfg.Loquacious, NHibernate.Validator, and NHibernate.Validator.Engine namespaces.

But it is also possible to do it with XML configuration; just make sure you add the following content to your App/Web.config file:

</configSections>

<nhv-configuration xmlns="urn:nhv-configuration-1.0">

<property name="default_validator_mode">UseExternal</property>

</nhv-configuration>

</configuration>

And include the following code:

XmlConfiguration xmlConfiguration = new XmlConfiguration();

ValidatorEngine validatorEngine = NHibernate.Validator.Cfg.Environment.SharedEngineProvider.GetEngine();

validatorEngine.Configure(validatorConfiguration);

cfg.Initialize(validatorEngine);

If you want, you can also have IntelliSense for the NHibernate Validator XML. If you added NHibernate Validator from NuGet, just copy the nhv-configuration.xsd and nhv-mapping.xsd files from the packages\NHibernate.Validator.1.3.2.4000\lib\Net35 folder to the C:\Program Files (x86)\Microsoft Visual Studio 10.0\Xml\Schemas or C:\Program Files (x86)\Microsoft Visual Studio 11.0\Xml\Schemas, depending on your Visual Studio version. See XML Configuration for more information on this. If you haven’t used NuGet, you will have to extract these files from the distribution .zip file or the source GitHub repository.

Next, we need to configure validations for our entities. First, using code:

FluentConfiguration validatorConfiguration = new FluentConfiguration();

validatorConfiguration.Register(new CustomerValidation()).SetDefaultValidatorMode(ValidatorMode.UseAttribute)

.IntegrateWithNHibernate.ApplyingDDLConstraints().RegisteringListeners();

The CustomerValidation class inherits from NHibernate.Validator.ValidationDef<T> and is defined as follows:

public class CustomerValidation : ValidationDef<Customer>

{

public CustomerValidation()

{

this.ValidateInstance.By((customer, context) => customer.Address != null && /* something else */ )

.WithMessage("The customer address is mandatory");

this.Define(x => x.Name).NotNullableAndNotEmpty().WithMessage("The customer name is mandatory");

this.Define(x => x.Name).MaxLength(50).WithMessage("The customer name can only have 50 characters");

this.Define(x => x.Email).NotNullableAndNotEmpty().WithMessage("The customer email is mandatory");

this.Define(x => x.Email).MaxLength(50).WithMessage("The customer email can only have 50 characters");

this.Define(x => x.Email).IsEmail().WithMessage("The customer email must be a valid email adddress");

}

And the same rules, except the ValidateInstanceBy custom validation can be defined in attributes like this:

public class Customer

{

[NotNullNotEmpty(Message = "The customer name is mandatory")]

[Length(Max = 50, Message = "The customer name can only have 50 characters")]

public virtual String Name { get; set; }

[NotNullNotEmpty(Message = "The customer email is mandatory")]

[Email(Message = "The customer email must be a valid email adddress")]

[Length(Max = 50, Message = "The customer email can only have 50 characters")]

public virtual String Email { get; set; }

[NotNull(Message = "The customer address is mandatory")]

public virtual Address Address { get; set; }

}

Tip: You need to reference the namespace NHibernate.Validator.Constraints.

You have to change the Validator configuration to use attributes:

FluentConfiguration validatorConfiguration = new FluentConfiguration();

validatorConfiguration.SetDefaultValidatorMode(ValidatorMode.UseAttribute)

.IntegrateWithNHibernate.ApplyingDDLConstraints().RegisteringListeners();

Finally, to use XML, you need to add a file named Customer.nhv.xml, place it in the same location as the Customer class, and mark it as an embedded resource, just as we saw on XML Mappings:

<?xml version="1.0" encoding="utf-8" ?>

<nhv-mapping namespace="Succinctly.Model" assembly="Succinctly.Model"

xmlns="urn:nhibernate-validator-1.0">

<notnull-notempty message="The customer name is mandatory"/>

</property>

<notnull-notempty message="The customer email is mandatory"/>

</property>

<not-null message="The customer address is mandatory"/>

</property>

</class>

</nhv-mapping>

You also have to tell NHibernate Validator to look for embedded resources explicitly:

FluentConfiguration validatorConfiguration = new FluentConfiguration();

validatorConfiguration.Register(new [] { typeof(Customer) })

.SetDefaultValidatorMode(ValidatorMode.UseExternal)

.IntegrateWithNHibernate.ApplyingDDLConstraints().RegisteringListeners();

For some properties, we are using the built-in validation mechanisms such as NotNullableAndNotEmpty and IsEmail whereas, in other cases, we are performing a custom check (the Address reference). Out-of-the-box validators include:

Included Validators

Validator	Type	Description
Digits/digits/decimalmax/ Decimalmin	Numbers, Strings	Validates the maximum number of digits/digits and fractional digits
FilePathExists/fileexists	Strings	Checks if a file path exists
GreaterThanOrEqualTo/min	Numbers	Checks if a number is greater or equal to a given value
HasValidElements/isvalid	Collections	Checks if all of the collections’ elements are valid recursively
IncludedBetween/range	Numbers	Checks if a number is included within a range (inclusive)
IsCreditCardNumber/ Creditcardnumber	Strings	Checks if a string matches a credit card number
IsEAN/ean	Numbers, Strings	Checks if a string or number matches an EAN
IsEmail/email	Strings	Checks if a string is a valid e-mail address
IsFalse/assertfalse	Booleans	Checks that a boolean is false
IsIBAN/iban	Strings	Checks that a string is a valid IBAN
IsInTheFuture/future	Dates and Times	Checks that a date is in the future
IsInThePast/past	Dates and Times	Checks that a date is in the past
IsIP/ipaddress	Strings	Checks that a string is a valid IP address
IsNumeric/digits	Strings	Checks that a string is a valid number
IsTrue/asserttrue	Booleans	Checks that a boolean is true
IsValid/valid	Entities	Checks that an entity is valid recursively
LengthBetween/length	Strings	Checks that the length of a string is contained within given limits
LessThanOrEqualTo/max	Numbers	Checks that a number is less or equal to a given value
MatchWith/pattern	Strings	Check that a string matches a regular expression
MaxLength/length	Strings	Checks the maximum length of a string
MaxSize/size	Collections	Checks the maximum size of a collection
MinLength/length	Strings	Checks the minimum length of a string
MinSize/size	Collections	Checks the minimum size of a collection
NotEmpty/not-empty	String, Collections, GUIDs	Checks if a string/collection/GUID is not empty
NotNullable/not-null	Any	Checks that a value is not null
NotNullableAndNotEmpty/ notnull-notempty	String, Collections	Checks that a string/collection is not null and contains values
Satisfy	Any	A custom rule, as a lambda expression
SizeBetween/size	Collections	Checks that a collection’s size is contained within given limits
Whitih/range	Numbers	Checks if a number is included within a range (exclusive)

Some of these validations can be implemented on the database in the form of the maximum length for a string and as check constraints. In this case, if NHibernate Validator is integrated with NHibernate using the ApplyingDDLConstraints/apply_to_ddl option, when the model is generated, it will include these checks.

Finally, you can implement your own attributes by inheriting from EmbeddedRuleArgsAttribute and implementing a couple of interfaces:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]

public sealed class IsEvenAttribute : EmbeddedRuleArgsAttribute, IRuleArgs, IValidator,

IPropertyConstraint

{

public IsEvenAttribute()

{

this.Message = "Number is odd";

}

public String Message { get; set; }

public Boolean IsValid(Object value, IConstraintValidatorContext constraintValidatorContext)

{

Int32 number = Convert.ToInt32(value);

return ((number % 2) == 0);

}

public void Apply(Property property)

{

Column column = property.ColumnIterator.OfType<Column>().First();

column.CheckConstraint = String.Format("({0} % 2 = 0)", column.Name);

}

This validator checks that a number is even, and can even change the property to which it is applied in order to add this check at the database level. That is what the IPropertyConstraint is for and you don’t have to implement it because, sometimes, a validation cannot be expressed easily in database terms.

To add the attribute by XML, add a <rule> tag to Customer.nhv.xml that references your custom attribute:

</rule>

</property>

Finally, let me just say this: Validation occurs when NHibernate tries to save an entity with validations attached but you can also validate explicitly:

InvalidValue[] invalidValuesObtainedExplicitly = validatorEngine.Validate(entity);

And that’s just about it. Happy validating!

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Validation

NHibernate Validator

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