基于ABP VNext及CodeFirst，迈开走向DDD的第一步

　　　前言:　DDD的基础知识这里就不讲了，网上有很多，无外乎架构从以外的三层变成四层，有聚合、实体、值对象、领域服务等这些概念，我也是最近看了很多，但无从下手，正好我们现有的项目是基于ABP

框架的，虽说也支持DDD,也是分为了4个项目，有领域有Domain，但感觉还是个三层项目，想了想，最大的问题还是收到新的任务后，总是从数据库开始，然后T4生成实体，没有太多的去进行领域划分。所以本次

我们使用EFCore的CodeFirst和ABPVnext来体验一下怎么在项目中真正的运用DDD。

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　　新建项目

　　我这里使用ABP的CLI命令创建的，当然也可以直接在网站（https://www.abp.io/get-started）上下载

　　我这里由于没有装mssql,所以切换到了mysql,具体可参考https://docs.abp.io/zh-Hans/abp/latest/Entity-Framework-Core-MySQL

切换后，我们使用下面这俩命令创建一下数据库

Add-Migration "Init"
Update-DataBase

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

重点来了

　　接下来我们正式从一个订单的领域开始，首先看一张图

首先我们先创建个地址的值对象　

  /// <summary>
    /// 地址(值对象)
    /// </summary>
    public class Address : ValueObject
    {
        public String Street { get; private set; }
        public String City { get; private set; }
        public String State { get; private set; }
        public String Country { get; private set; }
        public String ZipCode { get; private set; }

        public Address() { }

        public Address(string street, string city, string state, string country, string zipcode)
        {
            Street = street;
            City = city;
            State = state;
            Country = country;
            ZipCode = zipcode;
        }

        protected override IEnumerable<object> GetAtomicValues()
        {
            // Using a yield return statement to return each element one at a time
            yield return Street;
            yield return City;
            yield return State;
            yield return Country;
            yield return ZipCode;
        }
    }

创建实体

 /// <summary>
    /// 订单明细实体
    /// </summary>
    public class OrderItem : Entity
    {
        public virtual Guid OrderId { get; protected set; }

        public virtual Guid ProductId { get; protected set; }

        public virtual int Count { get; protected set; }

        protected OrderItem()
        {

        }

        internal OrderItem(Guid orderId, Guid productId, int count)
        {
            OrderId = orderId;
            ProductId = productId;
            Count = count;
        }

        internal void ChangeCount(int newCount)
        {
            Count = newCount;
        }

        public override object[] GetKeys()
        {
            return new Object[] { OrderId, ProductId };
        }
    }

创建订单聚合根

 /// <summary>
    /// 订单聚合根
    /// </summary>
    public class Order : AggregateRoot<Guid>
    {
        public virtual string ReferenceNo { get; protected set; }

        public virtual int TotalItemCount { get; protected set; }

        public virtual DateTime CreationTime { get; protected set; }

        public virtual List<OrderItem> OrderLines { get; protected set; }

        public Address Address { get; protected set; }//值对象

        public string UserName { get; protected set; }

        protected Order()
        {

        }

        public Order(Guid id, string referenceNo, string userName, Address address)
        {
            Check.NotNull(referenceNo, nameof(referenceNo));

            Id = id;
            ReferenceNo = referenceNo;
            Address = address;
            OrderLines = new List<OrderItem>();
            CreationTime = DateTime.Now;
            UserName = userName;
        }

        public void AddProduct(Guid productId, int count)
        {
            if (count <= 0)
            {
                throw new ArgumentException(
                    "You can not add zero or negative count of products!",
                    nameof(count)
                );
            }

            var existingLine = OrderLines.FirstOrDefault(ol => ol.ProductId == productId);

            if (existingLine == null)
            {
                OrderLines.Add(new OrderItem(this.Id, productId, count));
            }
            else
            {
                existingLine.ChangeCount(existingLine.Count + count);
            }

            TotalItemCount += count;
        }
    }

然后在Context中添加

public DbSet<Order> Orders { get; set; }

public DbSet<OrderItem> OrderItems { get; set; }

public static void ConfigureDDDTest(this ModelBuilder builder)
        {
            Check.NotNull(builder, nameof(builder));

            /* Configure your own tables/entities inside here */

            //builder.Entity<YourEntity>(b =>
            //{
            //    b.ToTable(DDDTestConsts.DbTablePrefix + "YourEntities", DDDTestConsts.DbSchema);

            //    //...
            //});

            builder.Entity<Order>(b =>
            {
                b.ToTable(DDDTestConsts.DbTablePrefix + "Orders", DDDTestConsts.DbSchema);
                b.ConfigureByConvention();
                b.OwnsOne(o => o.Address, a => {
                    a.WithOwner();
                });
                //b.Property(x => x.Name).IsRequired().HasMaxLength(128);
            });

            builder.Entity<OrderItem>(b =>
            {
                b.ToTable(DDDTestConsts.DbTablePrefix + "OrderLines", DDDTestConsts.DbSchema);
                b.ConfigureByConvention();
                b.HasKey(x => new { x.OrderId, x.ProductId });
                //b.Property(x => x.Name).IsRequired().HasMaxLength(128);
            });
        }

此时我们再执行迁移命令，会发现数据库中多了俩张表，值对象在聚合中

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

这时候我们执行个创建的方法是，会出现这个错误。

这个时候只需要把 base.OnModelCreating(builder);，移到builder.ConfigureDDDTest();下面即可

自定义仓储的话，我们需要把接口定义在领域层，把实现放在基础设施层

 public class OrderRepository : EfCoreRepository<DDDTestDbContext, Order, Guid>, IOrderRepository
    {
        public OrderRepository(IDbContextProvider<DDDTestDbContext> dbContextProvider)
     : base(dbContextProvider)
        {

        }

        public async Task<Order> Get(Guid orderId)
        {

            var order = await DbContext
                               .Orders
                               .Include(x => x.Address)
                               .FirstOrDefaultAsync(o => o.Id == orderId);
            if (order == null)
            {
                order = DbContext
                            .Orders
                            .Local
                            .FirstOrDefault(o => o.Id == orderId);
            }
            if (order != null)
            {
                await DbContext.Entry(order)
                    .Collection(i => i.OrderLines).LoadAsync();
            }

            return order;
        }
    }

整体实现下来，不知道有没有点对DDD的感觉呢？

参考：　　

https://www.cnblogs.com/richieyang/p/5373250.html
https://cn.abp.io/blog/Abp/Abp-vNext-Announcement
https://docs.abp.io/en/abp/latest/
https://github.com/abpframework/abp/issues/2640
https://docs.microsoft.com/zh-cn/dotnet/architecture/microservices/microservice-ddd-cqrs-patterns/microservice-domain-model
https://github.com/dotnet-architecture/eShopOnContainers