DatabaseDelete.md

Database.Delete()

In this lesson, we will learn about possible ways to delete a record from the database. M# provides Database.Delete() method for this purpose, which requires an entity instance to be deleted from database.

M# provides three overloads of Database.Delete() method. In this lesson, we will work with the Employee entity and will see how we can call Database.Delete() on an entity instance(s).

Note: In the codes below, the keyword this represents the current instance of an Employee entity.

Soft Deleting

M# allows developers to soft delete records in the database. You can mark an entity as Soft Delete in M# and calling Database.Delete() method on the entity instances updates the .Deleted special column on the record as True, rather than deleting the record permanently.

Setting an Entity as Soft Delete

You can mark an entity as Soft Delete by selecting SoftDelete(); method on the Entity in M# Model Management Section, as shown below:

For more information on entities in M#, please read lesson M# Concepts.

using MSharp;

namespace Domain
{
    public class Employee : SubType<User>
    {
        public Employee()
        {
            SoftDelete();

            String("Code");
        }
    }
}

M# updates the entity class and marks the class with [SoftDelete] attribute, as in our case the Employee entity class is marked as Soft Delete, as shown below:

/// <summary>Represents an instance of Employee entity type.</summary>
[SoftDelete]
[EscapeGCop("Auto generated code.")]
public partial class Employee : User

M# creates a new column on the SQL Table shown below to manage soft delete records.

Overloads

Task Delete(IEntity instance);
Task Delete(IEntity instance, DeleteBehaviour behaviour);
Task Delete<T>(IEnumerable<T> instances) where T : IEntity;

Example

/// Delete Single Employee Record
Database.Delete(this);

// Delete Collection of Employee Records
Database.Delete(lstEmployees);

// Delete Single Employee with Delete behaviour
Database.Delete(this,DeleteBehaviour.BypassDeleting);

The code above shows that we are deleting a record of Employee, also supplying an additional parameter DeleteBehaviour. The additional parameter is used in special cases when you want to bypass any event in the workflow of the Database.Delete() method. DeleteBehaviour enum and the events raised by M# while deleting an instance are discussed below.

Events Raised During Database.Delete

protected override Task OnDeleting(CancelEventArgs e)
{
    // Perform any pre-deleting business logic. Fires just befor an instance is deleted
    return base.OnDeleting(e);
}

protected override Task OnDeleted(EventArgs e)
{
    // Perform any post-deleting business logic. Fires just after an instance is deleted
    return base.OnDeleted(e);
}

Delete Behaviour Enum

M# provides Database.Delete() method overload with an extra parameter of an enum type DeleteBehaviour. This enum type is used to bypass the events raised while deleting an entity instance as required in the business logic, the enum options are shown below:

namespace Olive.Entities
{
    [Flags]
    public enum DeleteBehaviour
    {
        Default = 1,
        BypassDeleting = 2,
        BypassDeleted = 4,
        BypassLogging = 8,
        BypassAll = 14
    }
}