Validating a single entity object is is quite useful in a web applications. In most web applications, the entity object is processed as soon as it is added or modified. But in some applications, the batch processing can be a better option. In a batch mode, you need to deal with multiple entity objects.

1. Validating Multiple Objects

The “DbContext” class has the “GetValidationErrors()” method to validate “Added” and “Modified” objects in the context. It returns a collection of “DbEntityValidationResult” objects.

public class DbContext
{
  public IEnumerable<DbEntityValidationResult> GetValidationErrors();
}

Before validating entities, the “GetValidationErrors()” calls the “DetectChanges()“.

2. Data Annotations

Let’s validate 2 entities.

public class MyCategory
{
  public int Id { get; set; }

  [MaxLength(5, ErrorMessage = "Category Name should be less than 5 characters.")]
  public string Name { get; set; }
}

public class MyProduct
{
  public int Id { get; set; }

  [Required(ErrorMessage="The product name is required")]
  public string Name { get; set; }
}

public class MyProductContext : DbContext
{
  public DbSet<MyCategory> Categories { get; set; }
  public DbSet<MyProduct> Products { get; set; }
}

public static class ValidationTest
{
  public static void DoValidation()
  {
    MyCategory c = new MyCategory { Id = 1, Name = "Toy" }; // Valid
    MyProduct p = new MyProduct { Id=1, Name = ""};

    using (MyProductContext context = new MyProductContext())
    {
      context.Categories.Add(c);
      context.Products.Add(p);

      c.Name = "Long Name"; // Invalid

      foreach (DbEntityValidationResult result in context.GetValidationErrors())
      {
        Console.WriteLine("{0} is Valid? {1}", result.Entry.Entity.ToString(), result.IsValid);

        foreach (DbValidationError e in result.ValidationErrors)
        {
          Console.WriteLine("{0}: {1}", e.PropertyName, e.ErrorMessage);
        }
      }
    }
  }
}

The output is like this:

MyCategory is Valid ? False
Name: Category Name should be less than 5 characters.
MyProduct is Valid ? False
Name: The product name is required