Entity Framework。多个 DbContext 多个数据库。 MySQL。代码优先

Question

我们有一个测试 Code First 项目，其中我们有两个 DbContext，每个都与它们自己的数据库匹配。

ApplicationDbContext:

using MultipleDbContext.Entities;
using MultipleDbContext.EntityConfigurations;
using System.Data.Entity;

namespace MultipleDbContext
{
    [DbConfigurationType(typeof(MySql.Data.Entity.MySqlEFConfiguration))]
    public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext() : base("ApplicationDBContext") {}

    public DbSet<Application> Applications { get; set; }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
            base.OnModelCreating(modelBuilder);

             modelBuilder.Configurations.Add(new ApplicationUserConfiguration());
            modelBuilder.Configurations.Add(new ApplicationConfiguration());

        }
    }
}

ApplicationUserDbContext:

using MultipleDbContext.Entities;
using MultipleDbContext.EntityConfigurations;
using System.Data.Entity;

namespace MultipleDbContext
{
    [DbConfigurationType(typeof(MySql.Data.Entity.MySqlEFConfiguration))]
    public class ApplicationUserDbContext : DbContext
    {
         public ApplicationUserDbContext() : base("UserDBContext") {

    }

        public DbSet<ApplicationUser> ApplicationUsers { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
         modelBuilder.Configurations.Add(new ApplicationUserConfiguration());
         }
    }
}

实体类：

申请：

using System.Collections.Generic;

namespace MultipleDbContext.Entities
{
    public class Application
    {
        public int ApplicationID { get; set; }
        public string ApplicationName { get; set; }
        public int UserID { get; set; }
        public virtual ApplicationUser PrimaryUser { get; set; }
    }
}

和应用程序用户

namespace MultipleDbContext.Entities
{
    public class ApplicationUser
    {
        public int UserID { get; set; }
        public string Name { get; set; }
    }
}

应用程序有一个 FK UserID，它映射到我们的 ApplicationUser。

using MultipleDbContext.Entities;
using System.Data.Entity.ModelConfiguration;

namespace MultipleDbContext.EntityConfigurations
{
    public class ApplicationConfiguration : EntityTypeConfiguration<Application>
    {
        public ApplicationConfiguration()
        {
            HasKey(x => x.ApplicationID);
            Property(x => x.ApplicationID).IsRequired();
            Property(x => x.ApplicationName).IsRequired();
            HasRequired(x => x.PrimaryUser).WithMany().HasForeignKey(x => x.UserID);

        }
    }
}

当我运行在 ApplicationUser 上更新数据库时，它工作正常。但是当我尝试在 ApplicationDbContext 上运行 update-database 时，它会抛出一个错误：

update-database -ConfigurationTypeName MultipleDbContext.Migrations.Configuration -verbose
Using StartUp project 'MultipleDbContext'.
Using NuGet project 'MultipleDbContext'.
Specify the '-Verbose' flag to view the SQL statements being applied to the target database.
Target database is: 'test' (DataSource: test, Provider: MySql.Data.MySqlClient, Origin: Configuration).
Applying explicit migrations: [201611021534507_Initial].
Applying explicit migration: 201611021534507_Initial.
System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Data.Entity.Migrations.DbMigrator.<ExecuteStatementsInternal>b__32(MigrationStatement s)
   at System.Linq.Enumerable.WhereListIterator`1.MoveNext()
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection, DbInterceptionContext interceptionContext)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatementsInternal(IEnumerable`1 migrationStatements, DbConnection connection)
   at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClass30.<ExecuteStatements>b__2e()
   at System.Data.Entity.Infrastructure.DefaultExecutionStrategy.Execute(Action operation)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements, DbTransaction existingTransaction)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.ExecuteStatements(IEnumerable`1 migrationStatements)
   at System.Data.Entity.Migrations.DbMigrator.ExecuteOperations(String migrationId, VersionedModel targetModel, IEnumerable`1 operations, IEnumerable`1 systemOperations, Boolean downgrading, Boolean auto)
   at System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.ApplyMigration(DbMigration migration, DbMigration lastMigration)
   at System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   at System.Data.Entity.Migrations.Infrastructure.MigratorLoggingDecorator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId)
   at System.Data.Entity.Migrations.DbMigrator.UpdateInternal(String targetMigration)
   at System.Data.Entity.Migrations.DbMigrator.<>c__DisplayClassc.<Update>b__b()
   at System.Data.Entity.Migrations.DbMigrator.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.EnsureDatabaseExists(Action mustSucceedToKeepDatabase)
   at System.Data.Entity.Migrations.DbMigrator.Update(String targetMigration)
   at System.Data.Entity.Migrations.Infrastructure.MigratorBase.Update(String targetMigration)
   at System.Data.Entity.Migrations.Design.ToolingFacade.UpdateRunner.Run()
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.AppDomain.DoCallBack(CrossAppDomainDelegate callBackDelegate)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Run(BaseRunner runner)
   at System.Data.Entity.Migrations.Design.ToolingFacade.Update(String targetMigration, Boolean force)
   at System.Data.Entity.Migrations.UpdateDatabaseCommand.<>c__DisplayClass2.<.ctor>b__0()
   at System.Data.Entity.Migrations.MigrationsDomainCommand.Execute(Action command)
Object reference not set to an instance of an object.

我做错了什么？

Answer 1

在进行更多研究后，我发现一篇文章说您不能从其他上下文中获得 FK，因为 EF 6 尚不支持它。

https://forums.asp.net/t/1953426.aspx?Foreign+Key+to+Different+Database+in+Code+First+Approach

四处走走，在我的迁移中，我手动创建了一个 SQL("") 来创建这个外键。

Entity Framework。多个 DbContext 多个数据库。 MySQL。代码优先

Entity Framework. Multiple DbContext Multiple Databases. MySQL. Code First

c#

mysql

entity-framework

entity-framework-migrations