1   <ItemGroup>
2     <PackageReference Include="Microsoft.EntityFrameworkCore.SqlServer" Version="2.0.1" />
3     <PackageReference Include="Microsoft.EntityFrameworkCore.Tools" Version="2.0.1" />
4   </ItemGroup>

 1     public class DBCoreFirst : DbContext
 2     {
 3         public DBCoreFirst() : base()
 4         {
 5
 6         }
 7
 8         public DBCoreFirst(DbContextOptions<DBCoreFirst> options)
 9             : base(options)
10         {
11
12         }
13
14         override protected void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
15         {
16             base.OnConfiguring(optionsBuilder);
17         }
18
19         #region 数据表
20
21         public DbSet<DT_User> DT_User { get; set; }
22
23         #endregion
24
25     }

1     public class DT_User
2     {
3         /// <summary>
4         /// 默认int类型ID为主键
5         /// 必须有一个字段为主键，不然会报错
6         /// </summary>
7         public int ID { get; set; }
8         public string UserName { get; set; }
9     }

1 Add-Migration DBCoreFirst

GenericArguments[0], 'Models.Migrations.DBCoreFirst',
on 'Microsoft.EntityFrameworkCore.Design.IDesignTimeDbContextFactory`1[TContext]' violates the constraint of type 'TContext'.

genericarguments [ 0 ]，”模型。迁移。dbcorefirst '，'微软。entityframeworkcore。设计。idesigntimedbcontextfactory ` 1 [ tcontext ]“违背类型的tcontext约束。

Could not load assembly 'WebFront'. Ensure it is referenced by the startup project 'Models'.未能加载程序集“webfront”。确保它由启动项目的“Models”引用。

Your target project 'WebFront' doesn't match your migrations assembly 'Models'. Either change your target project or change your migrations assembly.

你的目标项目webfront不迁移组件模型匹配”。要么更改目标项目，要么更改迁移程序集。

services.AddDbContext<DBCoreFirst>(options => options.UseSqlServer(connection));
改为
services.AddDbContext<DBCoreFirst>(options => options.UseSqlServer(connection, c => c.MigrationsAssembly("WebFront")));

GenericArguments[0], 'Models.Migrations.DBCoreFirst',
on 'Microsoft.EntityFrameworkCore.Design.IDesignTimeDbContextFactory`1[TContext]' violates the constraint of type 'TContext'.genericarguments [ 0 ]，”模型。迁移。dbcorefirst '，'微软。entityframeworkcore。
设计。idesigntimedbcontextfactory ` 1 [ tcontext ]“违背类型的tcontext约束。

Add-Migration DBCodeFirst
改为
Add-Migration DBLog