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

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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

 1 public partial class Language : BaseEntity<int> 2     { 3         private ICollection<LocaleStringResource> _localeStringResources; 4  5         /// <summary> 6         /// Gets or sets the name 7         /// </summary> 8  9         public string Name { get; set; }10 11         /// <summary>12         /// Gets or sets the language culture13         /// </summary>14 15         public string LanguageCulture { get; set; }16 17         /// <summary>18         /// Gets or sets the unique SEO code19         /// </summary>20 21         public string UniqueSeoCode { get; set; }22 23         /// <summary>24         /// Gets or sets the flag image file name25         /// </summary>26 27         public string FlagImageFileName { get; set; }28 29         /// <summary>30         /// Gets or sets a value indicating whether the language supports "Right-to-left"31         /// </summary>32 33         public bool Rtl { get; set; }34 35 36         /// <summary>37         /// Gets or sets a value indicating whether the language is published38         /// </summary>39 40         public bool Published { get; set; }41 42         /// <summary>43         /// Gets or sets the display order44         /// </summary>45 46         public int DisplayOrder { get; set; }47 48         public bool IsDefault { get; set; }49 50         /// <summary>51         /// Gets or sets locale string resources52         /// </summary>53         public virtual ICollection<LocaleStringResource> LocaleStringResources54         {55             get { return _localeStringResources ?? (_localeStringResources = new HashSet<LocaleStringResource>()); }56             protected set { _localeStringResources = value; }57         }

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语言资源(LocaleStringResource):

 1 public partial class LocaleStringResource : BaseEntity<int> 2     { 3         /// <summary> 4         /// Gets or sets the language identifier 5         /// </summary> 6         public int LanguageId { get; set; } 7  8         /// <summary> 9         /// Gets or sets the resource name10         /// </summary>11         public string ResourceName { get; set; }12 13         /// <summary>14         /// Gets or sets the resource value15         /// </summary>16         public string ResourceValue { get; set; }17 18         /// <summary>19         /// Gets or sets a value indicating whether this resource was installed by a plugin20         /// </summary>21         public bool? IsFromPlugin { get; set; }22 23         /// <summary>24         /// Gets or sets a value indicating whether this resource was modified by the user25         /// </summary>26         public bool? IsTouched { get; set; }27 28         /// <summary>29         /// Gets or sets the language30         /// </summary>31         public virtual Language Language { get; set; }32 33     }

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其中语言及资源主外键关系配置如下

 1  public partial class LanguageMapper : IEntityTypeConfiguration<Language> 2     { 3         public void Configure(EntityTypeBuilder<Language> builder) 4         { 5             builder.ToTable("Language"); 6             builder.HasKey(r => r.Id); 7             builder.HasIndex(r => r.LanguageCulture); 8             builder.HasIndex(r => r.Name); 9             builder.HasIndex(r => r.UniqueSeoCode);10         }11     }

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 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：

 1  public class TechCategory:BaseEntity<int> 2     { 3         /// <summary> 4         /// 名称 5         /// </summary> 6         public string Name { get; set; } 7         /// <summary> 8         /// 分类描述 9         /// </summary>10         public string Descript { get; set; }11         /// <summary>12         /// meta标题13         /// </summary>14         public string MetaTitle { get; set; }15         /// <summary>16         /// meta描述17         /// </summary>18         public string MetaDescript { get; set; }19         /// <summary>20         /// 缩略图21         /// </summary>22         public string Thumb { get; set; }23         /// <summary>24         /// 图片25         /// </summary>26         public string Image { get; set; }27         /// <summary>28         /// 排序29         /// </summary>30         public int Sort { get; set; }31         /// <summary>32         /// 父级分类33         /// </summary>34         public int? ParentId { get; set; }35         36         /// <summary>37         /// 父级分类38         /// </summary>39 40         public virtual TechCategory Parent { get; set; }41         public virtual ICollection<Technology> Technologys { get; set; }42         /// <summary>43         /// 子级44         /// </summary>45         public virtual ICollection<TechCategory> Childs { get; set; }46         /// <summary>47         /// 关键词48         /// </summary>49         public string Slug { get; set; }50         /// <summary>51         /// 创建时间52         /// </summary>53         public long CreatedOn { get; set; }54     }

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 1  public class TechCategoryMapper : IEntityTypeConfiguration<TechCategory> 2     { 3         public void Configure(EntityTypeBuilder<TechCategory> builder) 4         { 5             builder.ToTable("TechCategory"); 6             builder.HasKey(r => r.Id); 7             builder.HasMany(r => r.Childs).WithOne(x => x.Parent) 8              .HasForeignKey(fk => fk.ParentId); 9             builder.HasIndex(r => r.Name);10         }11     }

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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

 1  public class DefaultContext : DbContext 2     { 3         public DefaultContext(DbContextOptions<DefaultContext> opt) 4             :base(opt) 5         { 6             AutoCommitEnabled = true; 7         } 8   protected override void OnModelCreating(ModelBuilder builder) 9         {10             base.OnModelCreating(builder);11             var mappingInterface = typeof(IEntityTypeConfiguration<>);12             // Types that do entity mapping13             var mappingTypes = GetType().GetTypeInfo().Assembly.GetTypes()14                 .Where(x => x.GetInterfaces().Any(y => y.GetTypeInfo().IsGenericType && y.GetGenericTypeDefinition() == mappingInterface));15 16             // Get the generic Entity method of the ModelBuilder type17             var entityMethod = typeof(ModelBuilder).GetMethods()18                 .Single(x => x.Name == "Entity" &&19                         x.IsGenericMethod &&20                         x.ReturnType.Name == "EntityTypeBuilder`1");21 22             foreach (var mappingType in mappingTypes)23             {24 25                 // Get the type of entity to be mapped26                 var genericTypeArg = mappingType.GetInterfaces().Single().GenericTypeArguments.Single();27 28                 // Get the method builder.Entity<TEntity>29                 var genericEntityMethod = entityMethod.MakeGenericMethod(genericTypeArg);30 31                 // Invoke builder.Entity<TEntity> to get a builder for the entity to be mapped32                 var entityBuilder = genericEntityMethod.Invoke(builder, null);33 34                 // Create the mapping type and do the mapping35                 var mapper = Activator.CreateInstance(mappingType);36                 mapper.GetType().GetMethod("Configure").Invoke(mapper, new[] { entityBuilder });37             }38             foreach (var relationship in builder.Model.GetEntityTypes().SelectMany(e => e.GetForeignKeys()))39             {40                 relationship.DeleteBehavior = DeleteBehavior.Restrict;41             }42         }43     }

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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

1  <ItemGroup>2     <PackageReference Include="Microsoft.EntityFrameworkCore" Version="2.0.0" />3     <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.0.0" />4     <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.0" />5     <PackageReference Include="Pomelo.EntityFrameworkCore.MySql" Version="2.0.0-rtm-10058" />6   </ItemGroup>

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