DimonSmart.Specification.EntityFrameworkCore 1.0.3

Specification Pattern Implementation in C#

Overview

The Specification Pattern is a behavioral design pattern that allows you to define reusable and composable query specifications. It is commonly used in scenarios where you need to filter, order, and include related entities in a query. The main idea behind this pattern is to encapsulate the logic of a query into separate specification classes, which can then be combined and reused to build complex queries.

In this C# implementation of the Specification Pattern, we have two parts:

1. Classical Specification (Specification class)

The classical specification provides the core functionality to build query specifications. It contains methods to define filtering criteria (Where), sorting (OrderBy, OrderByDesc), and logical operations (And, Or) to combine multiple specifications together.

Usage Example:

var specification = Specification<Student>
    .Create()
    .Where(s => s.Age < 21)
    .OrderBy(s => s.Name)
    .OrderByDesc(s => s.Age);

2. Specification for use with EntityFrameworkCore (EFCoreSpecification)

The EntityFrameworkCore support extends the classical specification with EF-specific operations, such as Include and ThenInclude, to eagerly load related entities in the query.

Usage Example:

var specification = EFCoreSpecification<Student>
    .Create()
    .Where(s => s.Age < 21)
    .Include(s => s.School.MainBook.Author);

Executing Specifications

To execute the specifications, you can use extension methods on the DBContext provided.

var under21 = _testDBContext.BySpecification(specification).ToList();

Custom Specifications

Developers can create their custom specification classes by inheriting from the Specification<TEntity> class and pass parameters through the constructor.

Example:

public class CustomStudentSpecification : Specification<Student>
{
    public CustomStudentSpecification(int minAge, string schoolName)
    {
        Where(s => s.Age >= minAge && s.School.Name == schoolName);
    }
}

Conclusion

The Specification Pattern in C# allows you to create reusable and composable query specifications for different data access scenarios. By providing EntityFrameworkCore support, you can efficiently use these specifications in Entity Framework queries, enhancing query performance and readability.

Remember that you can also create custom specification classes by inheriting from the base Specification class, making the pattern even more flexible and adaptable to various business requirements.