一起学ASP.NET Core 2.0学习笔记(二): ef core2.0 及mysql provider 、Fluent API相关配置及迁移

不得不说微软的技术迭代还是很快的，上了微软的船就得跟着她走下去，前文一起学ASP.NET Core 2.0学习笔记(一): CentOS下 .net core2 sdk nginx、supervisor、mysql环境搭建搭建好了.net core linux的相关环境，今天就来说说ef core相关的配置及迁移:

简介:

Entity Framework(以下简称EF) 是微软以 ADO.NET 为基础所发展出来的对象关系对应 (O/R Mapping) 解决方案，EF Core是Entity framework得下一版本,相比EF原来版本(4-6.1)，显得更加轻量级,相比同样出身名门的dapper还是显得有点庞大,不过鱼与熊掌向来不可兼得,想想一堆堆语法糖,方便的linq查询以及lambda表达式,可以很大程度上从T-SQL语法上脱身出来很多,在配置过程中也碰到一些问题，记录下来,以便后期翻阅:

一.poco的创建以及Fluent Api关系配置

1.一对多关系:

项目中最常见的就是一对多关系了,以语言及语言为例

语言(Language)类

 public partial class Language : BaseEntity<int>
     {
         private ICollection<LocaleStringResource> _localeStringResources;

         /// <summary>
         /// Gets or sets the name
         /// </summary>

         public string Name { get; set; }

         /// <summary>
         /// Gets or sets the language culture
         /// </summary>

         public string LanguageCulture { get; set; }

         /// <summary>
         /// Gets or sets the unique SEO code
         /// </summary>

         public string UniqueSeoCode { get; set; }

         /// <summary>
         /// Gets or sets the flag image file name
         /// </summary>

         public string FlagImageFileName { get; set; }

         /// <summary>
         /// Gets or sets a value indicating whether the language supports "Right-to-left"
         /// </summary>

         public bool Rtl { get; set; }

         /// <summary>
         /// Gets or sets a value indicating whether the language is published
         /// </summary>

         public bool Published { get; set; }

         /// <summary>
         /// Gets or sets the display order
         /// </summary>

         public int DisplayOrder { get; set; }

         public bool IsDefault { get; set; }

         /// <summary>
         /// Gets or sets locale string resources
         /// </summary>
         public virtual ICollection<LocaleStringResource> LocaleStringResources
         {
             get { return _localeStringResources ?? (_localeStringResources = new HashSet<LocaleStringResource>()); }
             protected set { _localeStringResources = value; }
         }

语言资源(LocaleStringResource):

 public partial class LocaleStringResource : BaseEntity<int>
     {
         /// <summary>
         /// Gets or sets the language identifier
         /// </summary>
         public int LanguageId { get; set; }

         /// <summary>
         /// Gets or sets the resource name
         /// </summary>
         public string ResourceName { get; set; }

         /// <summary>
         /// Gets or sets the resource value
         /// </summary>
         public string ResourceValue { get; set; }

         /// <summary>
         /// Gets or sets a value indicating whether this resource was installed by a plugin
         /// </summary>
         public bool? IsFromPlugin { get; set; }

         /// <summary>
         /// Gets or sets a value indicating whether this resource was modified by the user
         /// </summary>
         public bool? IsTouched { get; set; }

         /// <summary>
         /// Gets or sets the language
         /// </summary>
         public virtual Language Language { get; set; }

     }

其中语言及资源主外键关系配置如下

  public partial class LanguageMapper : IEntityTypeConfiguration<Language>
     {
         public void Configure(EntityTypeBuilder<Language> builder)
         {
             builder.ToTable("Language");
             builder.HasKey(r => r.Id);
             builder.HasIndex(r => r.LanguageCulture);
             builder.HasIndex(r => r.Name);
             builder.HasIndex(r => r.UniqueSeoCode);
         }
     }

 public partial class LocaleStringResourceMapper : IEntityTypeConfiguration<LocaleStringResource>
    {
        public void Configure(EntityTypeBuilder<LocaleStringResource> builder)
        {
            builder.ToTable("LocaleStringResource");
            builder.HasKey(r => r.Id);
            builder.HasIndex(r => r.LanguageId);
            builder.HasIndex(r => r.ResourceName);
            builder.HasOne(r => r.Language).WithMany(b => b.LocaleStringResources)
                .HasForeignKey(fk => fk.LanguageId);
        }
    }

2、父子关系 ：

  public class TechCategory:BaseEntity<int>
     {
         /// <summary>
         /// 名称
         /// </summary>
         public string Name { get; set; }
         /// <summary>
         /// 分类描述
         /// </summary>
         public string Descript { get; set; }
         /// <summary>
         /// meta标题
         /// </summary>
         public string MetaTitle { get; set; }
         /// <summary>
         /// meta描述
         /// </summary>
         public string MetaDescript { get; set; }
         /// <summary>
         /// 缩略图
         /// </summary>
         public string Thumb { get; set; }
         /// <summary>
         /// 图片
         /// </summary>
         public string Image { get; set; }
         /// <summary>
         /// 排序
         /// </summary>
         public int Sort { get; set; }
         /// <summary>
         /// 父级分类
         /// </summary>
         public int? ParentId { get; set; }

         /// <summary>
         /// 父级分类
         /// </summary>

         public virtual TechCategory Parent { get; set; }
         public virtual ICollection<Technology> Technologys { get; set; }
         /// <summary>
         /// 子级
         /// </summary>
         public virtual ICollection<TechCategory> Childs { get; set; }
         /// <summary>
         /// 关键词
         /// </summary>
         public string Slug { get; set; }
         /// <summary>
         /// 创建时间
         /// </summary>
         public long CreatedOn { get; set; }
     }

  public class TechCategoryMapper : IEntityTypeConfiguration<TechCategory>
     {
         public void Configure(EntityTypeBuilder<TechCategory> builder)
         {
             builder.ToTable("TechCategory");
             builder.HasKey(r => r.Id);
             builder.HasMany(r => r.Childs).WithOne(x => x.Parent)
              .HasForeignKey(fk => fk.ParentId);
             builder.HasIndex(r => r.Name);
         }
     }

二、数据库上下文:

根据前面创建的相关实体类 以及相关mapper类型，我们可以重现DbContext的OnModelCreating的方法,反射出实现了IEntityTypeConfiguration接口的相关mapper类型创建相关实体-数据表的相关对应关系

  public class DefaultContext : DbContext
     {
         public DefaultContext(DbContextOptions<DefaultContext> opt)
             :base(opt)
         {
             AutoCommitEnabled = true;
         }
   protected override void OnModelCreating(ModelBuilder builder)
         {
             base.OnModelCreating(builder);
             var mappingInterface = typeof(IEntityTypeConfiguration<>);
             // Types that do entity mapping
             var mappingTypes = GetType().GetTypeInfo().Assembly.GetTypes()
                 .Where(x => x.GetInterfaces().Any(y => y.GetTypeInfo().IsGenericType && y.GetGenericTypeDefinition() == mappingInterface));

             // Get the generic Entity method of the ModelBuilder type
             var entityMethod = typeof(ModelBuilder).GetMethods()
                 .Single(x => x.Name == "Entity" &&
                         x.IsGenericMethod &&
                         x.ReturnType.Name == "EntityTypeBuilder`1");

             foreach (var mappingType in mappingTypes)
             {

                 // Get the type of entity to be mapped
                 var genericTypeArg = mappingType.GetInterfaces().Single().GenericTypeArguments.Single();

                 // Get the method builder.Entity<TEntity>
                 var genericEntityMethod = entityMethod.MakeGenericMethod(genericTypeArg);

                 // Invoke builder.Entity<TEntity> to get a builder for the entity to be mapped
                 var entityBuilder = genericEntityMethod.Invoke(builder, null);

                 // Create the mapping type and do the mapping
                 var mapper = Activator.CreateInstance(mappingType);
                 mapper.GetType().GetMethod("Configure").Invoke(mapper, new[] { entityBuilder });
             }
             foreach (var relationship in builder.Model.GetEntityTypes().SelectMany(e => e.GetForeignKeys()))
             {
                 relationship.DeleteBehavior = DeleteBehavior.Restrict;
             }
         }
     }

三、多数据库支持:

多数据库的支持，并不是意味着同时对多种数据库操作，当然，后面，我们会尝试同时对多种数据库操作，这可能需要多个上下文，暂且不论。分布式数据库。我们的项目可能是在windows上开发的使用的是SqlServer，我们要发布到linux上，SqlServer 2017 据说是支持liunx的，但是还没出... 当然不是说 SqlServer 就不能装在liunx上，但是我们的Liunx服务器可能已经安装了MySql或 Oracle，我们希望使用现有的，又或者是，我们需要切换数据库。那么，我们需要可以随时切换数据库的支持，以上篇的mysql为例：

1.引用相关包，mysql我用的Pomelo.EntityFrameworkCore.MySql，国人开发的mysql for ef core的相关服务对象,ef

core 2.0中需要指定2.0版本(Install-Package Pomelo.EntityFrameworkCore.MySql -Version 2.0.0-rtm-10059),

2.需改配置文件依据相关配置动态加载数据库提供对象；相关代码及配置如下

nuget引用列表

  <ItemGroup>
     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.0.0" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.0.0" />
     <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.0" />
     <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="2.0.0-rtm-10058" />
   </ItemGroup>

相关配置文件修改

 "ConnectionStrings": {
    "MongoDbConnectionString": "mongodb://tchistory:tc123456@127.0.0.1/history",
    "ConnectionString": "Data Source=127.0.0.1;Initial Catalog=farmdata;User ID=root;Password=123456",
    "DataProvider": "MySql"
  },

在startup.cs 的configureServices方法中添加数据库上下文

        public void ConfigureServices(IServiceCollection services)
        {
            services.AddDbContext<DefaultContext>(option => option.UseFarmDatabase(Configuration));
            services.UseFarmService(Configuration);
            services.AddMvc();

        }

数据库提供对象扩展方法如下:

public static DbContextOptionsBuilder UseFarmDatabase(this DbContextOptionsBuilder optionsBuilder, IConfiguration configuration)
{
string provider = configuration.GetConnectionString("DataProvider"), connection = configuration.GetConnectionString("ConnectionString");
if (provider.Equals(DataBaseServer.SqlServer, StringComparison.InvariantCultureIgnoreCase))
{
return optionsBuilder.UseSqlServer(connection);
}
else if (provider.Equals(DataBaseServer.MySql, StringComparison.InvariantCultureIgnoreCase))
{
return optionsBuilder.UseMySql(connection);
}
else
{
throw Error.Argument("UseDatabaseServer", "No databaseProvider");
}
}

在程序包管理控制台添加相关迁移 命令 add-migration init:  会在当前目录下生成相关迁移目录

执行update-database -Verbose提交更改到数据库,这样数据库迁移及更改就算完成了,其中要注意的地方是ef core 2.0 中有些数据库提供对象暂时是没有完全实现，如用Pomelo.EntityFrameworkCore.MySql -Version 1.1.2 可能会报方法未实现，更新2.0 rtm版本即可。

祝愿你在码农道路上越走越顺畅;