为 class 库创建 Entity Framework 核心迁移

Question

我正在尝试在 EF Core class 库中生成迁移，但到目前为止无济于事。我正在使用包管理器控制台（Visual Studio 2017 社区）编写如下命令：

PM> Add-Migration Update37

但我总是得到一个错误：

Unable to create an object of type 'DBContext'. Add an implementation of 'IDesignTimeDbContextFactory' to the project, or see https://go.microsoft.com/fwlink/?linkid=851728 for additional patterns supported at design time.

我的解决方案结构：

如您所见，我有 2 个项目，其中 MesDBModels 是 class 库，我想为其生成到 Migrations 文件夹的迁移。我添加了 DummyProject 以便在 .NETcore 运行时提供 "Startup project"。 DummyProject 还包含 DBContextFactory class 中 IDesignTimeDBContextFactory<> 接口的实现。 DummyProject 还包含对 MesDBModels 项目的引用。

MesDBModels.Database.DBContext :

using MesDBModels.FluentConfig;
using MesDBModels.Models;
using Microsoft.EntityFrameworkCore;

namespace MesDBModels.Database
{
public class DBContext : DbContext
{
    public DBContext(DbContextOptions<DBContext> options) : base(options) { }

    protected override void OnModelCreating(ModelBuilder modelBuilder)
    {
        modelBuilder.ApplyConfiguration(new AccessCardConfig());
        modelBuilder.ApplyConfiguration(new AlarmConfig());
        modelBuilder.ApplyConfiguration(new BitPositionConfig());
        modelBuilder.ApplyConfiguration(new MachineConfig());
        modelBuilder.ApplyConfiguration(new ParameterTemplateConfig());
        modelBuilder.ApplyConfiguration(new ReferenceConfig());
        modelBuilder.ApplyConfiguration(new ReferenceTemplateConfig());
        modelBuilder.ApplyConfiguration(new UserConfig());
        modelBuilder.ApplyConfiguration(new UserGroupConfig());
        modelBuilder.ApplyConfiguration(new UserPermissionConfig());

        base.OnModelCreating(modelBuilder);
    }

    public DbSet<AccessCard> AccessCards { get; set; }
    public DbSet<Alarm> Alarms { get; set; }
    public DbSet<AlarmDefinition> AlarmDefinitions { get; set; }
    public DbSet<AlarmPriority> AlarmPriorities { get; set; }
    public DbSet<BitPosition> BitPositions { get; set; }
    public DbSet<EventLog> EventLogs { get; set; }
    public DbSet<EventType> EventTypes { get; set; }
    public DbSet<Group> Groups { get; set; }
    public DbSet<Machine> Machines { get; set; }
    public DbSet<MachineState> MachineStates { get; set; }
    public DbSet<MachineStateDefinition> MachineStateDefinitions { get; set; }
    public DbSet<Permission> Permissions { get; set; }
    public DbSet<ParameterTemplate> ParameterTemplates { get; set; }
    public DbSet<ReferenceParameterHistory> ReferenceParameterHistory { get; set; }
    public DbSet<ParameterValueLimit> ParameterValueLimits { get; set; }
    public DbSet<Reference> References { get; set; }
    public DbSet<ReferenceParameterType> ReferenceParameterTypes { get; set; }
    public DbSet<ReferenceTemplate> ReferenceTemplates { get; set; }
    public DbSet<Session> Sessions { get; set; }
    public DbSet<Unit> Units { get; set; }
    public DbSet<UnitStatus> UnitStatuses { get; set; }
    public DbSet<User> Users { get; set; }
    public DbSet<UserGroup> UserGroups { get; set; }
    public DbSet<UserPermission> UsersPermissions { get; set; }
}

}

DummyProject.DBContextFactory :

using Microsoft.EntityFrameworkCore;
using Microsoft.EntityFrameworkCore.Design;

namespace MesDBModels
{
public class DBContextFactory : IDesignTimeDbContextFactory<DbContext>
{ 
    public DbContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<DbContext>();
        builder.UseSqlServer(
            "Server=(local)\serverName;Database=dbName;Trusted_Connection=True;MultipleActiveResultSets=true");

        return new DbContext(builder.Options);
    }
}

}

DummyProject.Program class :

using System;

namespace DummyProject
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

所以我的问题是：我做错了什么？我试图将 DBContextFactory class 与 DBContext class 一起放入 MesDBModels 项目中，但结果是一样的。我已经关注了这个：还有这个： https://garywoodfine.com/using-ef-core-in-a-separate-class-library-project/ 但也许我误解了某些事情或做错了什么。

请帮忙。

Answer 1

您在

中输入错误

public class DBContextFactory : IDesignTimeDbContextFactory<DbContext>
{ 
    public DbContext CreateDbContext(string[] args)
    {
        var builder = new DbContextOptionsBuilder<DbContext>();
        builder.UseSqlServer(
            "Server=(local)\serverName;Database=dbName;Trusted_Connection=True;MultipleActiveResultSets=true");

        return new DbContext(builder.Options);
    }
}

当尝试构造您的 DBContext 时，框架会为 DBContext 寻找 IDesignTimeDbContextFactory，但您却为基础 DbContext 实现了一个工厂。将这段代码中的 DbContext 修改为 DBContext 应该可以了。

为 class 库创建 Entity Framework 核心迁移

Create Entity Framework Core migration for class library

c#

entity-framework-migrations

entity-framework-core

.net-core