标签：
visual studio 2015 community update 3 + .net core tools(preview2) + sqlserver2012 express
win10（版本14393）+ .net core(版本 1.0.0-preview2-003121)
AirMusic
Asp.net core WebApi（这里不用mvc模板，是因为mvc模板初始的内容太多，这里用不到）
记得去年第一次做项目，用了asp.net mvc5,因此也第一接触了EntityFramework（版本是EF6）。 现在打算用asp.net core来完成一个项目，air music是学习asp.net core时新建的demo项目，以后学习core中遇到的一些问题一般会从这个项目产生，今天这篇文章是在migration初始化数据库时发生的一些问题。
public class Song { public int Id { get; set; } [Required] public string SongName { get; set; } public virtual ICollection<ArtistSong> Artists { get; set; } public virtual ICollection<SongListSong> SongLists { get; set; } } //歌手 public class Artist { public int Id { get; set; } [Required] public string Name { get; set; } public virtual ICollection<Album> Albums { get; set; } public virtual ICollection<ArtistSong> Songs { get; set; } } //song with artist n:n table public class ArtistSong { [Key] public int ArtistId { get; set; } [Key] public int SongId { get; set; } } //专辑 public class Album { public int Id { get; set; } [Required] public string Title { get; set; } public virtual ICollection<Song> Songs { get; set; } } //歌单 public class SongList { public int Id { get; set; } [Required] public string Title { get; set; } public string Describe { get; set; } public virtual ApplicationUser User { get; set; } public virtual ICollection<SongListSong> Songs { get; set; } } // song with songlist n:n table public class SongListSong { [Key] public int SongListId { get; set; } [Key] public int SongId { get; set; } }
"Microsoft.AspNetCore.Identity.EntityFrameworkCore": "1.0.0"
（依赖了好多ef重要组件）"Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview2-final"
（引用了才可以试用migration）"Microsoft.EntityFrameworkCore.SqlServer": "1.0.0"
（我觉得是ef连接sqlserver的必须组件）还有就是必须在project.json里的tools节点中添加"Microsoft.EntityFrameworkCore.Tools": "1.0.0-preview2-final",不然输入命令”Add Migration“时就会报出下面这句错误。
"No parameterless constructor………“这句错误是因为ApplicationDbContext(数据库上下文类)没有写下面这个构造函数报的错误。
public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options) : base(options) { }
Webapi模板已经创建好了appsetting.json文件，这个文件的作用和web.config是一样的
在ApplicationDbContext重写的方法OnModelCreating中，有一行代码
base.OnModelCreating(builder)
当我把这行代码注释掉时，迁移过程中就会报出如下错误：
很明显，错误发生的原因是IdentityUser没有被映射到ApplicationDbContext,所以可以知道这句代码的作用，就是用来映射Identity的几个实体类的，没有这句，数据库中就不会自动生成Users、Roles……等Table了,我还没有去github看这个方法的源码，但我觉得实际上就是第一次Add-Migration时，生成的源文件ApplicationDbContextModelSnapshot.cs 中的代码：
protected override void BuildModel(ModelBuilder modelBuilder) { modelBuilder .HasAnnotation("ProductVersion", "1.0.0-rtm-21431") .HasAnnotation("SqlServer:ValueGenerationStrategy", SqlServerValueGenerationStrategy.IdentityColumn); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityRole", b => { b.Property<string>("Id"); b.Property<string>("ConcurrencyStamp") .IsConcurrencyToken(); b.Property<string>("Name") .HasAnnotation("MaxLength", 256); b.Property<string>("NormalizedName") .HasAnnotation("MaxLength", 256); b.HasKey("Id"); b.HasIndex("NormalizedName") .HasName("RoleNameIndex"); b.ToTable("AspNetRoles"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityRoleClaim<string>", b => { b.Property<int>("Id") .ValueGeneratedOnAdd(); b.Property<string>("ClaimType"); b.Property<string>("ClaimValue"); b.Property<string>("RoleId") .IsRequired(); b.HasKey("Id"); b.HasIndex("RoleId"); b.ToTable("AspNetRoleClaims"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUser", b => { b.Property<string>("Id"); b.Property<int>("AccessFailedCount"); b.Property<string>("ConcurrencyStamp") .IsConcurrencyToken(); b.Property<string>("Discriminator") .IsRequired(); b.Property<string>("Email") .HasAnnotation("MaxLength", 256); b.Property<bool>("EmailConfirmed"); b.Property<bool>("LockoutEnabled"); b.Property<DateTimeOffset?>("LockoutEnd"); b.Property<string>("NormalizedEmail") .HasAnnotation("MaxLength", 256); b.Property<string>("NormalizedUserName") .HasAnnotation("MaxLength", 256); b.Property<string>("PasswordHash"); b.Property<string>("PhoneNumber"); b.Property<bool>("PhoneNumberConfirmed"); b.Property<string>("SecurityStamp"); b.Property<bool>("TwoFactorEnabled"); b.Property<string>("UserName") .IsRequired() .HasAnnotation("MaxLength", 256); b.HasKey("Id"); b.HasIndex("NormalizedEmail") .HasName("EmailIndex"); b.HasIndex("NormalizedUserName") .IsUnique() .HasName("UserNameIndex"); b.ToTable("AspNetUsers"); b.HasDiscriminator<string>("Discriminator").HasValue("IdentityUser"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserClaim<string>", b => { b.Property<int>("Id") .ValueGeneratedOnAdd(); b.Property<string>("ClaimType"); b.Property<string>("ClaimValue"); b.Property<string>("UserId") .IsRequired(); b.HasKey("Id"); b.HasIndex("UserId"); b.ToTable("AspNetUserClaims"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserLogin<string>", b => { b.Property<string>("LoginProvider"); b.Property<string>("ProviderKey"); b.Property<string>("ProviderDisplayName"); b.Property<string>("UserId") .IsRequired(); b.HasKey("LoginProvider", "ProviderKey"); b.HasIndex("UserId"); b.ToTable("AspNetUserLogins"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserRole<string>", b => { b.Property<string>("UserId"); b.Property<string>("RoleId"); b.HasKey("UserId", "RoleId"); b.HasIndex("RoleId"); b.HasIndex("UserId"); b.ToTable("AspNetUserRoles"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserToken<string>", b => { b.Property<string>("UserId"); b.Property<string>("LoginProvider"); b.Property<string>("Name"); b.Property<string>("Value"); b.HasKey("UserId", "LoginProvider", "Name"); b.ToTable("AspNetUserTokens"); }); modelBuilder.Entity("AirMusic.Models.ApplicationUser", b => { b.HasBaseType("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUser"); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityRoleClaim<string>", b => { b.HasOne("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityRole") .WithMany("Claims") .HasForeignKey("RoleId") .OnDelete(DeleteBehavior.Cascade); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserClaim<string>", b => { b.HasOne("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUser") .WithMany("Claims") .HasForeignKey("UserId") .OnDelete(DeleteBehavior.Cascade); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserLogin<string>", b => { b.HasOne("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUser") .WithMany("Logins") .HasForeignKey("UserId") .OnDelete(DeleteBehavior.Cascade); }); modelBuilder.Entity("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUserRole<string>", b => { b.HasOne("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityRole") .WithMany("Users") .HasForeignKey("RoleId") .OnDelete(DeleteBehavior.Cascade); b.HasOne("Microsoft.AspNetCore.Identity.EntityFrameworkCore.IdentityUser") .WithMany("Roles") .HasForeignKey("UserId") .OnDelete(DeleteBehavior.Cascade); }); }
一个让我很困惑的问题在进行第一次Migration时出现了。AirMusic的实体中，有这样一种关系：
但是神奇的事情发生了（我不想这样的）：
migrationBuilder.CreateTable( name: "ArtistSongs", columns: table => new { ArtistId = table.Column<int>(nullable: false), SongId = table.Column<int>(nullable: false), //ArtistId1 = table.Column<int>(nullable: true) }, constraints: table => { table.PrimaryKey("PK_ArtistSongs", x => new { x.ArtistId, x.SongId }); table.ForeignKey( name: "FK_ArtistSongs_Artists_ArtistId", column: x => x.ArtistId, principalTable: "Artists", principalColumn: "Id", onDelete: ReferentialAction.Cascade); //table.ForeignKey( // name: "FK_ArtistSongs_Artists_ArtistId1", // column: x => x.ArtistId1, // principalTable: "Artists", // principalColumn: "Id", // onDelete: ReferentialAction.Restrict); table.ForeignKey( name: "FK_ArtistSongs_Songs_SongId", column: x => x.SongId, principalTable: "Songs", principalColumn: "Id", onDelete: ReferentialAction.Cascade); }); migrationBuilder.CreateTable( name: "SongListSongs", columns: table => new { SongListId = table.Column<int>(nullable: false), SongId = table.Column<int>(nullable: false), //SongListId1 = table.Column<int>(nullable: true) }, constraints: table => { table.PrimaryKey("PK_SongListSongs", x => new { x.SongListId, x.SongId }); table.ForeignKey( name: "FK_SongListSongs_Songs_SongId", column: x => x.SongId, principalTable: "Songs", principalColumn: "Id", onDelete: ReferentialAction.Cascade); table.ForeignKey( name: "FK_SongListSongs_SongLists_SongListId", column: x => x.SongListId, principalTable: "SongLists", principalColumn: "Id", onDelete: ReferentialAction.Cascade); //table.ForeignKey( // name: "FK_SongListSongs_SongLists_SongListId1", // column: x => x.SongListId1, // principalTable: "SongLists", // principalColumn: "Id", // onDelete: ReferentialAction.Restrict); });
自动添加了带artist1和songlist1的字段，我很希望知道的朋友告诉我解决的办法！！我实在不知道怎么让EF不自动添加这个多余的字段，所以我把那些多余的字段都注释掉后，才update-database到数据库:
song-artist[N:N] , song-songlist[N:N]
在ApplicationDbContext的OnModelCreating方法里，可以手动的配置数据库中的关系，像什么组合主键啦，组合外键啦等等各种约束，都可以 实现。特别是数据库中实体的关系配置（1:1,1:N,N:N）,例如：用方法builder.HasOne().WithMany()就可以建立[1:N]的关系。AirMusic初次Migration中，我也手动的配置了一些关系：
var entityAS=builder.Entity<ArtistSong>(); entityAS.HasKey("ArtistId", "SongId"); entityAS.HasOne<Artist>() .WithMany() .HasForeignKey("ArtistId"); var entitySS = builder.Entity<SongListSong>(); entitySS.HasKey("SongListId", "SongId"); entitySS.HasOne<SongList>() .WithMany() .HasForeignKey("SongListId");
上面代码的作用是，ArtistId和SongId设为ArtistSong的组合主键，ArtistSong的ArtistId设为Artist的外键。entitySS的作用也大致相同。
第一次完整的写一篇博文，晚上去吃饭是电脑自动重启更新了，vscode里的代码都没保存，打开博客园文章管理发现什么都没了，难过的就去听歌睡觉了。第二天起来打算从新来过时，发现有一行“自动保存恢复”，那个感觉就和中了100块的彩票一样。
希望有人看完这篇文章吧，新写手最需要的就是多给建议呀！谢谢
Asp.net core中Migration工具使用的交流分享
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原文地址：http://www.cnblogs.com/boomyao/p/5745525.html
