SpecificationPattern

Implementation of a Data Access pattern for Entity Framework

Description

This project maintains EF UnitOfWork (UoW) approach, but gets rid of repositories, using UoW directly.

IUnitOfWork interface exposes all the methods needed to query and modify data.

public interface IUnitOfWork
{
    ValueTask<TEntity?> GetById<TEntity>(object?[]? id, CancellationToken cancellationToken = default) 
		where TEntity : class;
    Task<List<TEntity>> List<TEntity>(CancellationToken cancellationToken = default) 
		where TEntity : class;
    Task<List<TProjection>> List<TEntity, TProjection>(Query<TEntity, TProjection> query, CancellationToken cancellationToken = default) 
		where TEntity : class;
    Task<TEntity?> FirstOrDefault<TEntity>(CancellationToken cancellationToken = default)
		where TEntity : class;
    Task<TProjection?> FirstOrDefault<TEntity, TProjection>(Query<TEntity, TProjection> query, CancellationToken cancellationToken = default)
		where TEntity : class;
    void Add<TEntity>(TEntity entity)
		where TEntity : class;
    void Update<TEntity>(TEntity entity)
		where TEntity : class;
    void Delete<TEntity>(TEntity entity)
		where TEntity : class;
}

To query data, the UoW uses the Query class, which represents the DB operation to read data. This way, it forces you to project the data to a specific class/dto, avoiding retrieving lots of data.

There are 3 query classes:

• Query<TEntity, TProjection>. Queries the TEntity DbSet and must return a TProjection item.
• SelfQuery<TEntity>. Queries the TEntity DbSet and must return the same TEntity.
• PaginatedQuery<TEntity, TProjection>. Has a constructor which receives a page number and page size, and paginates the response.

Examples

In the Specification.Examples project there are example queries and a service to view the usage of both elements.

Example query:

public class GetPeopleByNameQuery : Query<Person, GetPeopleByNameQueryDto>
{
    public string Name { get; }

    public GetPeopleByNameQuery(string name)
    {
        Name = name;
    }

    public override IQueryable<GetPeopleByNameQueryDto> Apply(IQueryable<Person> baseQuery)
    {
        return baseQuery.Where(x => x.FirstName == Name)
            .Select(x => new GetPeopleByNameQueryDto(x.FirstName + " " + x.LastName, x.BirthDate));
    }
}

public record GetPeopleByNameQueryDto(string CompleteName, DateTime BirthDate);

Because all the logic is in the query, services don't need extra mapping, so they end up being:

public Task<List<GetCatsWithOwnersQueryDto>> GetCats()
{
    var query = new GetCatsWithOwnersQuery();

    return _unitOfWork.List(query);
}