ProductQuery.cs

using System;
using System.Linq;
using System.Threading.Tasks;
using Catalog.Contracts;
using Microsoft.EntityFrameworkCore;

namespace Catalog
{
    public interface IProductQuery
    {
        Task<Product> GetProduct(Guid productId);
    }

    public class Product
    {
        public Guid Id { get; set; }
        public string Name { get; set; }
        public decimal Price { get; set; }
    }
    
    public class ProductQuery : IProductQuery
    {
        private readonly CatalogDbContext _dbContext;

        public ProductQuery(CatalogDbContext dbContext)
        {
            _dbContext = dbContext;
        }

        public async Task<Product> GetProduct(Guid productId)
        {
            return await _dbContext.Products
                .Where(x => x.Id == productId)
                .Select(x => new Product
                {
                    Id = x.Id,
                    Name = x.Name,
                    Price = x.Price
                })
                .SingleAsync();
        }
    }
}