C#C
C#•3y ago
M B V R K

DDD Specification with AND Operator

Hi dear friends,
Sorry because I know this topic is a bit of pain,

I'm working with DDD, as you know DDD came with a useful pain solution called Specifications,
Now I have the following interface that represents a Specification:
using System.Linq.Expressions;

namespace ExpenseService.Domain.Shared.Interfaces;

/// <summary>
/// Represents a specification that defines a condition that an entity must satisfy.
/// </summary>
/// <typeparam name="T">The type of entity.</typeparam>
public interface ISpecification<T> where T: class
{
    bool IsSatisfiedBy(T entity);

    Expression<Func<T, bool>> ToExpression();
    
    ISpecification<T> And(ISpecification<T> other);
}


And I have created an Abstract class who represents this specification as the following:
using System.Linq.Expressions;
using ExpenseService.Domain.Shared.Interfaces;

namespace ExpenseService.Domain.Specifications;


public abstract class Specification<T> : ISpecification<T> where T : class
{
    
    public abstract Expression<Func<T, bool>> ToExpression();


    public virtual bool IsSatisfiedBy(T entity)
    {
        var predicate = ToExpression().Compile();
        return predicate(entity);
    }
    
    
    public ISpecification<T> And(ISpecification<T> other)
    {

    }
}


The issue:
The issue is that And method I don't know how to well implement it, I will do a brief explaination,
All I want that method do is to take an ISpecification<T> and returns another/ a new ISpecification<T> that represents the First specification's expression combined with the second Specification's expression by 
AND
 operator.

I have tried the Github Copilot but it suggests on me to create a new specification called AndSpecification and that method should returns a new instance of that AndSpecification.

From your experience, what is the ideal/efficient implementation for that And method ??
Massive thanks in advance <3
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