Null exception on AlterColumn in 2.1

[christamlyn-bridge]

After upgrading to EF 2.1, an existing migration throws an null reference exception on a migration to Alter Column type.

{
    "Timestamp": "2018-06-28T16:12:10.7220699+01:00",
    "Level": "Fatal",
    "MessageTemplate": "Failed to migrate database.",
    "RenderedMessage": "Failed to migrate database.",
    "Exception": "System.NullReferenceException: Object reference not set to an instance of an object.\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.GetColumnType(String schema, String table, String name, Type clrType, Nullable`1 unicode, Nullable`1 maxLength, Nullable`1 fixedLength, Boolean rowVersion, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(AlterColumnOperation operation, IModel model, MigrationCommandListBuilder builder)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.<>c.<.cctor>b__72_4(MigrationsSqlGenerator g, MigrationOperation o, IModel m, MigrationCommandListBuilder b)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(MigrationOperation operation, IModel model, MigrationCommandListBuilder builder)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.GenerateUpSql(Migration migration)\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.<>c__DisplayClass13_2.<GetMigrationCommandLists>b__2()\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.MigrateAsync(String targetMigration, CancellationToken cancellationToken)\r\n   at Bridge.Framework.EntityFramework.WebHostExtensions.MigrateDatabase[T](T dbContext, ILogger`1 logger)",
    "Properties": {
        "SourceContext": "Bridge.EmployeeAttendance.Api.Repositories.EntityFramework.IApplicationDbContext",
        "EnvironmentUserName": "DESKTOP-0EKMJ8N\\daniel.campos",
        "MachineName": "DESKTOP-0EKMJ8N",
        "ProcessId": 6768,
        "ThreadId": 4,
        "Format": "json",
        "ExceptionDetail": {
            "Type": "System.NullReferenceException",
            "HResult": -2147467261,
            "Message": "Object reference not set to an instance of an object.",
            "Source": "Microsoft.EntityFrameworkCore.Relational",
            "StackTrace": "   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.GetColumnType(String schema, String table, String name, Type clrType, Nullable`1 unicode, Nullable`1 maxLength, Nullable`1 fixedLength, Boolean rowVersion, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(AlterColumnOperation operation, IModel model, MigrationCommandListBuilder builder)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.<>c.<.cctor>b__72_4(MigrationsSqlGenerator g, MigrationOperation o, IModel m, MigrationCommandListBuilder b)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(MigrationOperation operation, IModel model, MigrationCommandListBuilder builder)\r\n   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.GenerateUpSql(Migration migration)\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.<>c__DisplayClass13_2.<GetMigrationCommandLists>b__2()\r\n   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.MigrateAsync(String targetMigration, CancellationToken cancellationToken)\r\n   at Bridge.Framework.EntityFramework.WebHostExtensions.MigrateDatabase[T](T dbContext, ILogger`1 logger)"
        },
        "Environment": "Development",
        "Country": "Global",
        "Source": "Bridge Employee Attendance API"
    }
}

Steps to reproduce

protected override void Up(MigrationBuilder migrationBuilder) =>
            migrationBuilder.AlterColumn<DateTimeOffset>(
                name: "Date",
                schema: "schema",
                table: "ColumnName",
                type: "DATE",
                nullable: false,
                oldClrType: typeof(DateTimeOffset));

        protected override void Down(MigrationBuilder migrationBuilder) =>
            migrationBuilder.AlterColumn<DateTimeOffset>(
                name: "Date",
                schema: "schema",
                table: "ColumnName",
                nullable: false,
                oldClrType: typeof(DateTimeOffset),
                oldType: "DATE");

To get the migration to work in 2.1 required to explicitly define oldType in the Up. Is this now mandatory? It seems to have worked in previous versions without.

The following migrates successfully:

protected override void Up(MigrationBuilder migrationBuilder) => migrationBuilder.AlterColumn( name: "Date", schema: "schema", table: "ColumnName", type: "DATE", nullable: false, oldType: "DATETIMEOFFSET", oldClrType: typeof(DateTimeOffset));

    protected override void Down(MigrationBuilder migrationBuilder) =>
        migrationBuilder.AlterColumn<DateTimeOffset>(
            name: "Date",
            schema: "schema",
            table: "ColumnName",
            nullable: false,
            oldClrType: typeof(DateTimeOffset),
            oldType: "DATE");

### Further technical details
EF Core version: 2.1
Database Provider: SQL Server
Operating system:  Windows

The documentation suggests 

[ajcvickers]

@christamlyn-bridge Can you post the full stack trace?

[bricelam]

System.NullReferenceException: Object reference not set to an instance of an object.
  at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.GetColumnType(String schema, String table, String name, Type clrType, Nullable`1 unicode, Nullable`1 maxLength, Nullable`1 fixedLength, Boolean rowVersion, IModel model)
  at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(AlterColumnOperation operation, IModel model, MigrationCommandListBuilder builder)
  at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.<>c.<.cctor>b__72_4(MigrationsSqlGenerator g, MigrationOperation o, IModel m, MigrationCommandListBuilder b)
  at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(MigrationOperation operation, IModel model, MigrationCommandListBuilder builder)
  at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)
  at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)
  at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.GenerateUpSql(Migration migration)
  at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.<>c__DisplayClass13_2.<GetMigrationCommandLists>b__2()
  at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.MigrateAsync(String targetMigration, CancellationToken cancellationToken)
  at Bridge.Framework.EntityFramework.WebHostExtensions.MigrateDatabase[T](T dbContext, ILogger`1 logger)"

[bricelam]

@christamlyn-bridge What version of EF was used to generate this migration? (Look for modelBuilder.HasAnnotation("ProductVersion", "X.X.X") in the designer file.) Or was is handcrafted?

[Parmie]

I got this error with ProductVersion "2.2.3-servicing-35854". My situation looks the same. I'm trying to change a DateTime to DateTimeOffset, as advised in #4711. After changing the type on one property, I generated this migration:

        protected override void Up(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.AlterColumn<DateTimeOffset>(
                name: "TimeStamp",
                table: "StorageWeightChanges",
                nullable: false,
                oldClrType: typeof(DateTime));
        }

        protected override void Down(MigrationBuilder migrationBuilder)
        {
            migrationBuilder.AlterColumn<DateTime>(
                name: "TimeStamp",
                table: "StorageWeightChanges",
                nullable: false,
                oldClrType: typeof(DateTimeOffset));
        }

Stack trace looks the same as the one above:

System.NullReferenceException: Object reference not set to an instance of an object.
   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.GetColumnType(String schema, String table, String name, Type clrType, Nullable`1 unicode, Nullable`1 maxLength, Nullable`1 fixedLength, Boolean rowVersion, IModel model)
   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(AlterColumnOperation operation, IModel model, MigrationCommandListBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.<>c.<.cctor>b__73_4(MigrationsSqlGenerator g, MigrationOperation o, IModel m, MigrationCommandListBuilder b)
   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(MigrationOperation operation, IModel model, MigrationCommandListBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(MigrationOperation operation, IModel model, MigrationCommandListBuilder builder)
   at Microsoft.EntityFrameworkCore.Migrations.MigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)   at Microsoft.EntityFrameworkCore.Migrations.SqlServerMigrationsSqlGenerator.Generate(IReadOnlyList`1 operations, IModel model)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.GenerateUpSql(Migration migration)
   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.<>c__DisplayClass13_2.<GetMigrationCommandLists>b__2()
   at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.Migrate(String targetMigration)
   at Microsoft.EntityFrameworkCore.RelationalDatabaseFacadeExtensions.Migrate(DatabaseFacade databaseFacade)

[bricelam]

I'm not able to reproduce either case on 2.1.11 or 2.2.6. If anyone still has a project they can share, I can investigate further...

[Kolky]

I had the same issue (on a migration to 3.1.2, coming from 2.2.6); I fixed it by specifying on the mapping .HasColumnType("datetimeoffset(7)"). This added type: "datetimeoffset(7)" to each AlterColumn statement, which the code seemed to expect. As you can see in @Parmie's code he doesn't have that!