问题一：Add-Migration 时出现 此类问题一般都是模型类主键标识问题增加KEY即可解决
报错：
The entity type 'xxxx' requires a primary key to be defined. If you intended to use a keyless entity type, call 'HasNoKey' in 'OnModelCreating'. For more information on keyless entity types, see https://go.microsoft.com/fwlink/?linkid=2141943.
以上问题方案：
public class XXXX { **[Key]** public int UserID { get; set; }//用户识别ID 主键 public string UserNike { get; set; } }
问题二：
Add-Migration 时出现这类问题（我是因为我选了默认项目模型类）） 一般情况下是当前默认项目(可以切到需要生成的项目下)中缺少entity framework core 相关包，需引用包
报错：
Your target project '解决方案名' doesn't match your migrations assembly '默认项目'. Either change your target project or change your migrations assembly. Change your migrations assembly by using DbContextOptionsBuilder. E.g. options.UseSqlServer(connection, b => b.MigrationsAssembly("WebBlogFirst")). By default, the migrations assembly is the assembly containing the DbContext. Change your target project to the migrations project by using the Package Manager Console's Default project drop-down list, or by executing "dotnet ef" from the directory containing the migrations project.以上问题方案：
