Philiprehberger.Specification

Specification pattern implementation for composable, reusable query filters.

Installation

dotnet add package Philiprehberger.Specification

Usage

Define Specifications

using Philiprehberger.Specification;
using System.Linq.Expressions;

public class IsActive : Specification<User>
{
    public override Expression<Func<User, bool>> ToExpression()
        => user => user.IsActive;
}

public class HasMinimumAge : Specification<User>
{
    private readonly int _minimumAge;

    public HasMinimumAge(int minimumAge) => _minimumAge = minimumAge;

    public override Expression<Func<User, bool>> ToExpression()
        => user => user.Age >= _minimumAge;
}

Compose Specifications

var isActive = new IsActive();
var isAdult = new HasMinimumAge(18);

// Combine with And, Or, Not
var activeAdult = isActive.And(isAdult);
var inactiveOrMinor = isActive.Not().Or(isAdult.Not());

Check Entities

var spec = new IsActive().And(new HasMinimumAge(18));

bool satisfies = spec.IsSatisfiedBy(user);

Filter Queryables

var spec = new IsActive().And(new HasMinimumAge(18));

// Extension method
IQueryable<User> results = dbContext.Users.Where(spec);

// Or via evaluator
IQueryable<User> results = SpecificationEvaluator.Evaluate(dbContext.Users, spec);

Implicit Conversion

Expression<Func<User, bool>> expr = new IsActive();
var results = dbContext.Users.Where(expr);

API

Specification<T>

Member	Description
ToExpression()	Convert to a LINQ expression tree
IsSatisfiedBy(T entity)	Check if an entity satisfies the specification
implicit operator Expression<Func<T, bool>>	Implicit conversion to expression

SpecificationExtensions

Method	Description
And<T>(Specification<T>, Specification<T>)	Combine with logical AND
Or<T>(Specification<T>, Specification<T>)	Combine with logical OR
Not<T>(Specification<T>)	Negate with logical NOT

QueryableExtensions

Method	Description
Where<T>(IQueryable<T>, Specification<T>)	Filter a queryable using a specification

SpecificationEvaluator

Method	Description
Evaluate<T>(IQueryable<T>, Specification<T>)	Apply a specification to a queryable source

Development

dotnet build src/Philiprehberger.Specification.csproj --configuration Release

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License

MIT