当我创建DbContext时，它会跳过初始化程序。我启用了迁移，添加了初始迁移，并通过程序包管理器更新了数据库。前两个步骤成功完成，但是当update命令尝试初始化我的数据库时，它返回空引用异常。
上下文类：
public class MusicContext:DbContext
{
public DbSet<Album> Albums { get; private set; }
public DbSet<Artist> Artists { get; private set; }
public DbSet<Rating> Ratings { get; private set; }
public DbSet<Song> Songs { get; private set; }
public DbSet<User> Users { get; private set; }
private static MusicContext s_instance;
public MusicContext() : base("EntityDB")
{
Database.SetInitializer<MusicContext>(new MusicInitializer());
var ensureDllIsCopied = System.Data.Entity.SqlServer.SqlProviderServices.Instance;
}
private MusicContext(string conStr) : base(conStr)
{
Database.SetInitializer(new MusicInitializer());
var ensureDllIsCopied = System.Data.Entity.SqlServer.SqlProviderServices.Instance;
}
public static MusicContext GetContext(string conStr)
{
if(s_instance==null)
s_instance = new MusicContext(conStr);
return s_instance;
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
modelBuilder.Configurations.Add(new AlbumConfig());
modelBuilder.Configurations.Add(new ArtistConfig());
modelBuilder.Configurations.Add(new SongConfig());
modelBuilder.Configurations.Add(new UserConfig());
}
}`
配置类：
internal sealed class Configuration : DbMigrationsConfiguration<DAL.MusicContext>
{
public Configuration()
{
AutomaticMigrationsEnabled = false;
}
protected override void Seed(DAL.MusicContext context)
{
Artist art1 = new Artist()
{
Name = "Skillet",
CareerStart = 1996 ,
Albums =new List<Album>(),
Songs =new List<Song>()
};
Artist art2 = new Artist()
{
Name = "Rammstein",
CareerStart = 1993,
Albums = new List<Album>(),
Songs = new List<Song>()
};
Artist art3 = new Artist()
{
Name = "Sharleen Spiteri",
CareerStart = 1988,
Albums = new List<Album>(),
Songs = new List<Song>()
};
Album alb1 = new Album()
{
Name = "Rosenrot",
Year = 2005,
Genre = "Industial Metal",
Artists = new List<Artist>(),
Songs = new List<Song>()
};
Album alb2 = new Album()
{
Name = "Comatose",
Year = 2006,
Genre = "Alternative Metal",
Artists = new List<Artist>(),
Songs = new List<Song>()
};
Song song1 = new Song()
{
Name = "Don't Die Before I Do",
Year = 2005,
Album = alb1,
Artists = new List<Artist>(),
Ratings = new List<Rating>(),
Liked = new List<User>(),
Filename = @"some filename"
};
Song song2 = new Song()
{
Name = "Whispers in the Dark",
Year = 2006,
Album = alb2,
Artists = new List<Artist>(),
Ratings = new List<Rating>(),
Liked = new List<User>(),
Filename = @"some filename"
};
art1.Albums.Add(alb1);
art1.Songs.Add(song1);
art2.Albums.Add(alb2);
art2.Songs.Add(song2);
art3.Songs.Add(song1);
alb1.Songs.Add(song1);
alb2.Songs.Add(song2);
song1.Artists.Add(art1);
song1.Artists.Add(art3);
song2.Artists.Add(art2);
User admin = new User() {
Name = "Krakenus00",
Role = "ADMIN",
Ratings = new List<Rating>(),
Liked = new List<Song>()
};
UserInfo ui = new UserInfo
{
Email = DataProtection.Encrypt("adminpoint"),
PasswordStored = DataProtection.Encrypt("FullAccess"),
User = admin
};
Rating rating = new Rating() { User = admin, Song = song2, Value = 5 };
admin.Liked.Add(song2);
context.Albums.Add(alb1);
context.Albums.Add(alb2);
context.Artists.Add(art1);
context.Artists.Add(art2);
context.Artists.Add(art3);
context.Songs.Add(song1);
context.Songs.Add(song2);
context.Users.Add(admin);
context.Ratings.Add(rating);
context.SaveChanges();
}
}
我的自定义初始化程序的Seed()等于配置的。它继承了DropCreateDatabaseAlways<>
当我尝试向DbContext添加元素时抛出异常。 错误信息：
System.NullReferenceException：对象引用未设置为实例 一个对象。在DAL.Migrations.Configuration.Seed（MusicContext 上下文中） D：\ Work \ Courses \ Raindrop \ DAL \ Migrations \ Configuration.cs：第105行
在 System.Data.Entity.Migrations.DbMigrationsConfiguration1.OnSeed(DbContext context) at System.Data.Entity.Migrations.DbMigrator.SeedDatabase() at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.SeedDatabase() at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable1 endingMigrations，字符串targetMigrationId，字符串lastMigrationId）
在 System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade（IEnumerable`1 endingMigrations，字符串targetMigrationId，字符串lastMigrationId）
在System.Data.Entity.Migrations.DbMigrator.UpdateInternal（String targetMigration） System.Data.Entity.Migrations.DbMigrator。<> c__DisplayClasse.b__d（） 在 System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists（动作 mustSucceedToKeepDatabase） System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists（操作 mustSucceedToKeepDatabase） System.Data.Entity.Migrations.DbMigrator.Update（字符串 targetMigration） System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update（String targetMigration） System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.RunCore（） 在System.Data.Entity.Migrations.Design.ToolingFacade.BaseRunner.Run（） 对象引用未设置为对象的实例。
第105行的代码：context.Albums.Add(alb1);
答案 0 :(得分：0)
有3个问题：
User的{{1}}不可为空的字段。JoinDate具有私有集属性。这导致从DbContext引发NullReferenceException。