How Do I Preserve Custom Code Changes In Entity Model Classes

Question

4.00/5 (1 vote)

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Hi,

1) I am using the Database first approach in my project, below is a small sample to describe what i want to achieve in my actual project.

2) I have generated an entity model from my database which generates the following code:

C#

namespace Test
{
    using System;
    using System.Collections.Generic;

    public partial class Student
    {
        public Student()
        {
            this.Enrollments = new HashSet&amp;lt;Enrollment&amp;gt;();
        }

        public int StudentID { get; set; }
        public string LastName { get; set; }
        public string FirstName { get; set; }
        public System.DateTime EnrollmentDate { get; set; }

        public virtual ICollection&amp;lt;Enrollment&amp;gt; Enrollments { get; set; }
    }
}

3) I made some changes in the above given Student class, i added an attribute and a property:

C#

using System.ComponentModel.DataAnnotations;

[Required()]
public int StudentID { get; set; }

public string FullName { get; set; }

4) Then i updated the model from database "Update Model from Database", and lost all the changes which i made in the Student class.

I want to know if there is any way to preserve these changes after updating the model from database?

Any and all help will be highly appreciated.

Thanks

Posted 7-Mar-14 8:55am

User 5095898

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User 5095898 · Accepted Answer · 2014-03-07T09:59:00

Hey Phil,

I was going through articles online and found a concept called “Buddy” classes. Here is the code I just wrote but not tested till yet:

New Class:

C#

namespace Test
{
    public class StudentMetaData
    {

        [Required()]
        public int StudentID { get; set; }

        public string FullName { get; set; }

    }
}

Modified generated class:

C#

namespace Test
{
    using System;
    using System.Collections.Generic;
    using System.ComponentModel.DataAnnotations;

    [MetadataType(typeof(StudentMetaData))]
    public partial class Student
    {
        public Student()
        {
            this.Enrollments = new HashSet<Enrollment>();
        }

        public int StudentID { get; set; }
        public string LastName { get; set; }
        public string FirstName { get; set; }
        public System.DateTime EnrollmentDate { get; set; }

        public virtual ICollection<Enrollment> Enrollments { get; set; }
    }
}

thanks

phil.o · Accepted Answer · 2014-03-07T09:01:00

Solution 1

As this class is declared as partial, you have the ability to create your own file, in which you can declare the same partial class, with your own code.
The code generator will always replace the code in the original file, there's no way to skip it; on the contrary, it will never touch anything in your custom own file.
You just have to match namespace and class name.

Hope this helps.

Posted 7-Mar-14 9:01am

phil.o

Comments

[no name] 7-Mar-14 15:49pm

Hey Phil,

Thanks for your reply, do you mean something like this:

Code generator:

namespace Test
{
using System;
using System.Collections.Generic;

public partial class Student
{
public Student()
{
this.Enrollments = new HashSet<Enrollment>();
}

public int StudentID { get; set; }
public string LastName { get; set; }
public string FirstName { get; set; }
public System.DateTime EnrollmentDate { get; set; }

public virtual ICollection<Enrollment> Enrollments { get; set; }
}
}

My Code:

namespace Test
{
using System;
using System.Collections.Generic;
using System.ComponentModel.DataAnnotations;

public partial class Student
{
[Required()]
public int StudentID { get; set; }

public string FullName { get; set; }

}
}