.net core2.x 自动注入 Entity(实体对象到上下文)

概要：有点老套，因为早在 .net frmework的时候（core还没出来），我们在使用 ef(4.。。。6)的时候就已经这么用，这里我在搭建框架，所以随手写下，让后来人直接拿去用用。

1.使用前提

　　使用前我们一定要明白的是，通过fluent api去映射实体关系和属性的，也就是说core里面，要实现IEntityTypeConfiguration<TEntity>接口对象，示例如下：

public class UserRoleConfiguration : IEntityTypeConfiguration<UserRole>
    {
        public override void Configure(EntityTypeBuilder<UserRole> builder)
        {
            builder.HasMany(x => x.UserRolePermissionCollection).WithOne(x => x.UserRole).HasForeignKey(x => x.UserRoleID).IsRequired();
            builder.HasDataRole();
        }
    }

　　这时候我们可以在 DBContext的 onModelCreating中如下方式注入：

public class DbContextBase : DbContext, IDbContext
    {
        private readonly IEntityConfigurationFinder _configurationFinder;
        public DbContextBase(DbContextOptions options, IEntityConfigurationFinder configurationFinder)
            : base(options)
        {
            _configurationFinder = configurationFinder;
        }

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            Type contextType = GetType();
            IEntityRegister[] entityConfigures = _configurationFinder.GetEntityRegisters();
            foreach (var config in entityConfigures)
            {
                config.Apply(modelBuilder);
            }
        }
    }

　　这是其中一个实体的映射方式，假设我们有十几或几十个，那么我们需要在这些十几或者几十遍，累得慌吧，累就对了，所以换个方式实现：

　　我们在定义一个IEntityRegister对象，所有的 所有实体映射类都需要实现这个接口对象，接口如下：

public interface IEntityRegister
    {
        void Apply(ModelBuilder builder);
    }

　　同时修改上面的 roleEntityTypeConfiguration

public class UserRoleConfiguration : IEntityTypeConfiguration<UserRole>,IEntityRegister
    {
        public override void Configure(EntityTypeBuilder<UserRole> builder)
        {
            builder.HasMany(x => x.UserRolePermissionCollection).WithOne(x => x.UserRole).HasForeignKey(x => x.UserRoleID).IsRequired();
            builder.HasDataRole();
        }
        public void Apply(ModelBuilder modelBuilder){
            modelBuilder.ApplyConfiguration(this);
        }
    }

　　

　　这时候我们其他的几十个 实体的配置对象，依旧按照如上写法即可，现在我们要做的就是找到所有实现了IEntityRegister接口的对象，也就是实体的映射对象。

2.查找实体配置对象

　　之前我们在上一篇说 dependencyInjection对象的时候，有写过一个类，其中查找程序及对象的方法，这里我们就又用到了，再贴一次完整的：

　　接口实现：

/// <summary>
    ///     查找应用程序中的程序集对象
    /// </summary>
    public interface IAppAssemblyFinder
    {
        /// <summary>
        ///     查询所有程序集对象
        /// </summary>
        /// <param name="filterAssembly">是否排除非业务程序集对象</param>
        /// <returns></returns>
        Assembly[] FindAllAssembly(bool filterAssembly = true);
        /// <summary>
        ///     获取指定类型的对象集合
        /// </summary>
        /// <typeparam name="ItemType">指定的类型</typeparam>
        /// <param name="expression">
        ///     过滤表达式:
        ///         查询接口(type=>typeof(ItemType).IsAssignableFrom(type));
        ///         查询实体:type => type.IsDeriveClassFrom<ItemType>()
        /// </param>
        /// <param name="fromCache">是否从缓存查询</param>
        /// <returns></returns>
        Type[] FindTypes<ItemType>(Func<Type, bool> expression, bool fromCache = true) where ItemType : class;
    }

　　对应实现类：

public class AppAssemblyFinder : IAppAssemblyFinder
    {
        private List<Assembly> _assemblies = new List<Assembly>();

        public Assembly[] FindAllAssembly(bool filterAssembly = true)
        {
            var filter = new string[]{
                "System",
                "Microsoft",
                "netstandard",
                "dotnet",
                "Window",
                "mscorlib",
                "Newtonsoft",
                "Remotion.Linq"
            };
            //core中获取依赖对象的方式
            DependencyContext context = DependencyContext.Default;
            if (context != null)
            {
                List<string> names = new List<string>();
                string[] dllNames = context.CompileLibraries.SelectMany(m => m.Assemblies).Distinct().Select(m => m.Replace(".dll", "")).ToArray();
                if (dllNames.Length > )
                {
                    names = (from name in dllNames
                             let index = name.LastIndexOf('/') +
                             select name.Substring(index))
                          .Distinct()
                          .WhereIf(name => !filter.Any(name.StartsWith), filterAssembly)
                          .ToList();
                }
                return LoadFromFiles(names);
            }
            //传统方式
            string pathBase = AppDomain.CurrentDomain.BaseDirectory;
            string[] files = Directory.GetFiles(pathBase, "*.dll", SearchOption.TopDirectoryOnly)
                .Concat(Directory.GetFiles(pathBase, ".exe", SearchOption.TopDirectoryOnly))
                .ToArray();
            if (filterAssembly)
            {
                files = files.WhereIf(f => !filter.Any(n => f.StartsWith(n, StringComparison.OrdinalIgnoreCase)), filterAssembly).Distinct().ToArray();
            }
            _assemblies = files.Select(Assembly.LoadFrom).ToList();
            return _assemblies.ToArray();
        }

        /// <summary>
        /// 获取指定类型的对象集合
        /// </summary>
        /// <typeparam name="ItemType">指定的类型</typeparam>
        /// <param name="expression"> 过滤表达式: 查询接口(type=>typeof(ItemType).IsAssignableFrom(type)); 查询实体:type => type.IsDeriveClassFrom<ItemType>()</param>
        /// <param name="fromCache">是否从缓存查询</param>
        /// <returns></returns>
        public Type[] FindTypes<ItemType>(Func<Type, bool> expression, bool fromCache = true) where ItemType : class
        {
            List<Assembly> assemblies;
            if (fromCache) assemblies = _assemblies;
            if (_assemblies == null || _assemblies.Count() == )
                assemblies = this.FindAllAssembly().ToList();

            Type[] types = _assemblies.SelectMany(a => a.GetTypes())
                .Where(expression).Distinct().ToArray();

            return types;
        }
        /// <summary>
        ///    从文件加载程序集对象
        /// </summary>
        /// <param name="files">文件(名称集合)</param>
        /// <returns></returns>
        private static Assembly[] LoadFromFiles(List<string> files)
        {
            List<Assembly> assemblies = new List<Assembly>();
            files?.ToList().ForEach(f =>
            {
                AssemblyName name = new AssemblyName(f);
                try { Assembly assembly = Assembly.Load(name); assemblies.Add(assembly); } catch { }
            });
            return assemblies.ToArray();
        }

    }

　　需要注意的是，这个接口以及实现类，需要注册为 singleton对象，保证生命周期和应用程序一致，否则，参数的fromCache无效，性能也会急剧下降。

　　查找IEntityRegister对象：

public class EntityConfigFinder : IEntityConfigFinder
    {
        public EntityConfigFinder(IAppAssemblyFinder assemblyFinder)
        {
            _assemblyFinder = assemblyFinder;
        }

        private readonly IAppAssemblyFinder _assemblyFinder;

        public IEntityRegister[] EntityRegisters()
        {
            var baseType = typeof(IEntityRegister);
            var types = _assemblyFinder.FindTypes<IEntityRegister>(type => baseType.IsAssignableFrom(type));
            var entityRegisters = types.Select(t => (IEntityRegister)Activator.CreateInstance(t))?.ToArray();
            return entityRegisters;
        }
    }

　　这时候我们就可以很简单的使用了：

3.使用

public class DbContextBase : DbContext, IDbContext
    {
        public DbContextBase(DbContextOptions options, IEntityConfigFinder entityFinder)
            : base(options)
        {
            _entityConfigFinder = entityFinder;
        }

        private readonly IEntityConfigFinder _entityConfigFinder;

        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            var dbContextType = GetType();
            IEntityRegister[] entityRegisters = _entityConfigFinder.EntityRegisters();
            foreach (var entityConfig in entityRegisters)
            {
                entityConfig.RegistTo(modelBuilder);
                Console.WriteLine($"成功注册实体:{entityConfig.EntityType}");
            }
            Console.WriteLine($"成功注册实体:{entityRegisters.Length}个");
        }
    }
}

4.其他

　　在 ef(6.x)中我们使用EntityTypeConfiguration的时候，可以直接使用该对象，但是core中没有了，所以我们可以再封装一个实现类：

public abstract class EntityTypeConfigurationBase<TEntity, TKey> : IEntityTypeConfiguration<TEntity>, IEntityRegister
        where TEntity : class, IEntity<TKey>
    {
        /// <summary>
        /// 将当前实体类映射对象注册到数据上下文模型构建器中
        /// </summary>
        /// <param name="modelBuilder">上下文模型构建器</param>
        public void Apply(ModelBuilder modelBuilder)
        {
            modelBuilder.ApplyConfiguration(this);
        }

        /// <summary>
        /// 重写以实现实体类型各个属性的数据库配置
        /// </summary>
        /// <param name="builder">实体类型创建器</param>
        public abstract void Configure(EntityTypeBuilder<TEntity> builder);
    }

　　这时候，我们的实体的配置类只需要继承该类，并实现其方法就可以了，比如：

public class UserRoleConfiguration : EntityTypeConfigurationBase<UserRole, Guid>
    {
        public override void Configure(EntityTypeBuilder<UserRole> builder)
        {
            builder.HasMany(x => x.UserRolePermissionCollection).WithOne(x => x.UserRole).HasForeignKey(x => x.UserRoleID).IsRequired();
            builder.HasDataRole();
        }
    }

　　DbContext的 OnModelCreating中不变。

结束！