Implementing Entity Validation - ASP.NET Dynamic Data - page 241

var employee = new Employee();
employee.BirthDate = new DateTime(74, 1, 1);
context.Employees.AddObject(employee);
context.SaveChanges();
}
}
StringLengthAttribute
SQL Server allows you to specify the maximum length of values that can be stored in
columns of string types such as CHAR and VARCHAR . However, the errors it reports when
encountering values that are too long to be stored in the underlying database column
without data truncation do not include the actual column name. This makes debugging of
truncation errors unnecessarily difficult. Fortunately, the StringLengthAttribute can be
used to validate the string length before the data is sent to the database server. Here is
how you can extend the ProductName property of the Product entity class:
[Required]
[StringLength(40, MinimumLength = 2]
public object ProductName;
The StringLengthAttribute allows you to specify both minimum and maximum length
that a string value can have. The maximum length is required and specified as the first
argument of the constructor. The minimum length is optional and has to be specified
explicitly by including the name of the MinimumLength property in the constructor.
The following test method verifies how the StringLengthAttribute works by initializing the
ProductName property with a string that consists of 41 characters—one character too long. As
you would expect from a validation attribute, this code throws a ValidationException ,
which unlike the low-level SqlException includes the display name of the column that
caused the problem:
[TestMethod]
[ExpectedValidationException(MemberName = “ProductName” )]
public void ProductName_MustBe40CharactersOrLess()
{
using (new TransactionScope())
using (var context = new NorthwindEntities())
{
var product = new Product();
product.ProductName = new String('T', 41);
context.Products.AddObject(product);
context.SaveChanges();
}
}