在哪里放置函数和验证代码实体框架

Question

Where and how (code example would be great) can I remove business logic from auto generated class for example Customer.cs under my Model.edmx

When I edit something in the designer and then save that changes EF update class so I need to enter for example default values (I know I can set them in designer) again.

public Customer()
{
    this.Blocked = false;
    this.Code = "#00000";
    this.Contacts = new ObservableListSource<Contact>();
}

Also how to create/where to put some basic validation (this.Code cannot be empty string or null) ?

Thanks.

Answer 1

Classes generated by Entity Framework are marked with partial keyword and you can extend them adding new file and creating other part of the partial class. This also prevent your changes from being overwritten when you update the model.

And maybe what even more important, EF adds set of partial methods to every mapped property, which allows you to add your own validation logic:

On Property Changing - include code to execute before the change occurs, such as property validation. The value parameter is the value to which the property is changing. Implement this method to validate a property change before it occurs. To prevent the change from being made, you must throw an exception.

On Property Changed - include code to execute after the change occurs, such as logging the change.

from How to: Execute Business Logic During Scalar Property Changes

Your partial class should look like that:

public partial class Customer()
{
    partial void OnCodeChanging(string value) 
    {
        if(string.IsNullOrEmpty(value))
            throw new InvalidOperationException ("value cannot be null or empty");
    }

}

You have to make sure it exists in the same namespace as the other part, created by EF.

Answer 2

Check out this project I was working on... https://github.com/NickStrupat/EntityFrameworkCodeFirstTriggers

The NuGet is at... https://www.nuget.org/packages/EntityFrameworkCodeFirstTriggers/

You can put in logic which is executed when the entities are persisted (at SaveChanges() ).

customer.Inserting += (sender, args) => ((Customer)customer).Code = "Some default";