Entity

In Domain-Driven Design, entity (marked by IEntity in LeanCode CoreLibrary) is a concept used to model a distinct and identifiable object within the domain that is defined by its characteristics and identity. Entities are objects that have a distinct lifecycle and are distinguishable from other objects based on their unique identity.

Packages

Package	Link	Application in section
LeanCode.DomainModels		IEntity
LeanCode.DomainModels.Generators		Ids

Example

Let's define a class representing a assignment belonging to a project:

[TypedId(TypedIdFormat.PrefixedGuid, CustomPrefix = "assignment")]
public readonly partial record struct AssignmentId;

public class Assignment : IEntity<AssignmentId>
{
    public AssignmentId Id { get; private init; }
    public string Name { get; private set; }
    public AssignmentStatus Status { get; private set; }
    public EmployeeId? AssignedEmployee { get; private set; }

    public Project ParentProject { get; private init; }

    DateTime IOptimisticConcurrency.DateModified { get; set; }

    private Assignment() { }

    public static Assignment Create(Project parentProject, string name)
    {
        return new Assignment
        {
            Name = name,
            ParentProject = parentProject,
            Status = AssignmentStatus.NotStarted,
        };
    }

    public void Edit(string name)
    {
        Name = name;
    }

    public void AssignEmployee(EmployeeId employeeId)
    {
        AssignedEmployee = employeeId;
    }

    public void UnassignEmployee()
    {
        AssignedEmployee = null;
    }

    public void ChangeStatus(AssignmentStatus status)
    {
        Status = status;
    }

    public enum AssignmentStatus
    {
        NotStarted,
        InProgress,
        Finished,
    }
}

Notice that Assignment is not an aggregate root - it can only be accessed through the Project to which it belongs. Methods from the Assignment class should be executed within the context of the Project aggregate. This aligns with the principle that an aggregate should function as a singular unit of transaction, ensuring that modifications to a Assignment object occur exclusively within the context of a corresponding Project. Any attempt to modify a Assignment object without the associated Project context should be restricted to maintain data integrity.