使用Add-Migration无法添加多个迁移（Pomelo.EntityFrameworkCore.MySql）

问题描述 #

使用程序包管理器控制台的Add-Migration命令添加新迁移或空迁移时，触发空引用异常。

重现步骤 #

• 项目中已存在迁移文件
• 在程序包管理器控制台执行命令 Add-Migration Test 添加新迁移，或尝试添加空迁移

技术细节 #

• MySQL版本：8.0.32 MySQL Community Server
• 操作系统：Windows 10 22H2
• Pomelo.EntityFrameworkCore.MySql版本：7.0.0
• Microsoft.AspNetCore.App版本：6.0

已尝试方案 #

• 更换为MySql.Data/MySql.EntityFrameworkCore驱动后，迁移可正常执行，但无法将Blob数据保存至数据库
• 考虑采用双驱动方案，分别管理数据库结构与数据，已在Pomelo相关仓库提交对应问题

堆栈跟踪 #

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Initialize(ColumnOperation columnOperation, IColumn column, RelationalTypeMapping typeMapping, Boolean isNullable, IEnumerable`1 migrationsAnnotations, Boolean inline)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.InitializeColumnHelper(ColumnOperation columnOperation, IColumn column, Boolean inline)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Diff(IColumn source, IColumn target, DiffContext diffContext)+MoveNext()
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.MakeStringColumnsRequiredWithoutUnexpectedDefaultValue(IColumn source, IColumn target, IEnumerable`1 migrationOperations)+MoveNext()
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.SkipRedundantCharSetSpecifyingAlterColumnOperations(IEnumerable`1 migrationOperations)+MoveNext()
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.PostFilterOperations(IEnumerable`1 migrationOperations)+MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.DiffCollection[T](IEnumerable`1 sources, IEnumerable`1 targets, DiffContext diffContext, Func`4 diff, Func`3 add, Func`3 remove, Func`4[] predicates)+MoveNext()
   at System.Linq.Enumerable.ConcatIterator`1.MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Diff(ITable source, ITable target, DiffContext diffContext)+MoveNext()
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.PostFilterOperations(IEnumerable`1 migrationOperations)+MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.DiffCollection[T](IEnumerable`1 sources, IEnumerable`1 targets, DiffContext diffContext, Func`4 diff, Func`3 add, Func`3 remove, Func`4[] predicates)+MoveNext()
   at System.Linq.Enumerable.ConcatIterator`1.MoveNext()
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.PostFilterOperations(IEnumerable`1 migrationOperations)+MoveNext()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.Sort(IEnumerable`1 operations, DiffContext diffContext)
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.Sort(IEnumerable`1 operations, DiffContext diffContext)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.MigrationsModelDiffer.GetDifferences(IRelationalModel source, IRelationalModel target)
   at Pomelo.EntityFrameworkCore.MySql.Migrations.Internal.MySqlMigrationsModelDiffer.GetDifferences(IRelationalModel source, IRelationalModel target)
   at Microsoft.EntityFrameworkCore.Migrations.Design.MigrationsScaffolder.ScaffoldMigration(String migrationName, String rootNamespace, String subNamespace, String language)
   at Microsoft.EntityFrameworkCore.Design.Internal.MigrationsOperations.AddMigration(String name, String outputDir, String contextType, String namespace)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigrationImpl(String name, String outputDir, String contextType, String namespace)
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.AddMigration.<>c__DisplayClass0_0.<.ctor>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.<>c__DisplayClass3_0`1.<Execute>b__0()
   at Microsoft.EntityFrameworkCore.Design.OperationExecutor.OperationBase.Execute(Action action)
Object reference not set to an instance of an object.

内容的提问来源于stack exchange，提问作者M. Ours