The model for context 'PostgresContext' has pending changes.

[Oleh213]

Hi,

When we moved to .Net 9 and update packages we got this issue:

Unhandled exception. System.AggregateException: One or more errors occurred. (An error was generated for warning 'Microsoft.EntityFrameworkCore.Migrations.PendingModelChangesWarning': The model for context 'PostgresContext' has pending changes. Add a new migration before updating the database. See https://aka.ms/efcore-docs-pending-changes. This exception can be suppressed or logged by passing event ID 'RelationalEventId.PendingModelChangesWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.)
---> System.InvalidOperationException: An error was generated for warning 'Microsoft.EntityFrameworkCore.Migrations.PendingModelChangesWarning': The model for context 'PostgresContext' has pending changes. Add a new migration before updating the database. See https://aka.ms/efcore-docs-pending-changes. This exception can be suppressed or logged by passing event ID 'RelationalEventId.PendingModelChangesWarning' to the 'ConfigureWarnings' method in 'DbContext.OnConfiguring' or 'AddDbContext'.
at Microsoft.EntityFrameworkCore.Diagnostics.EventDefinition1.Log[TLoggerCategory](IDiagnosticsLogger1 logger, TParam arg)
at Microsoft.EntityFrameworkCore.Diagnostics.RelationalLoggerExtensions.PendingModelChangesWarning(IDiagnosticsLogger`1 diagnostics, Type contextType)
at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.ValidateMigrations(Boolean useTransaction)
at Microsoft.EntityFrameworkCore.Migrations.Internal.Migrator.Migrate(String targetMigration)
at Npgsql.EntityFrameworkCore.PostgreSQL.Migrations.Internal.NpgsqlMigrator.Migrate(String targetMigration)
at Microsoft.EntityFrameworkCore.RelationalDatabaseFacadeExtensions.Migrate(DatabaseFacade databaseFacade)
at WorkflowCore.Persistence.EntityFramework.Services.EntityFrameworkPersistenceProvider.EnsureStoreExists()
at WorkflowCore.Services.WorkflowHost.StartAsync(CancellationToken cancellationToken)
--- End of inner exception stack trace ---
at System.Threading.Tasks.Task.ThrowIfExceptional(Boolean includeTaskCanceledExceptions)
at System.Threading.Tasks.Task.Wait(Int32 millisecondsTimeout, CancellationToken cancellationToken)
at System.Threading.Tasks.Task.Wait()
at WorkflowCore.Services.WorkflowHost.Start()
at Cyclix.Workflow.WorkflowServiceCollectionExtensions.RegisterWorkflows(IApplicationBuilder app, Assembly[] assemblies)

.AddWorkflow(options => options.UsePostgreSQL(connectionString: appSettings.ConnectionStrings.PostgresWorkflowDb, true, true))

`

public static void RegisterWorkflows(this IApplicationBuilder app, params Assembly[] assemblies)
{
    var host = app.ApplicationServices.GetService<IWorkflowHost>();
    
    host.RegisterWorkflow<ShopServiceJobWorkflow, ShopServiceJobWorkflowContext>();
    host.RegisterWorkflow<CustomerServiceRequestWorkflow, CustomerServiceRequestWorkflowContext>();

    host.Start();
}

`

WorkflowCore 3.13.0
WorkflowCore.Persistence.PostgreSQL 3.13.0
Microsoft.EntityFrameworkCore 9.0.1

P.S: Creating a new migration didn't solve this issue

[chrrust]

In my interactive view in Rider I evaluated workflowDbContext.Database.HasPendingModelChanges() to true inside EntityFrameworkPersistenceProvider.EnsureStoreExists().

Because of this, I tried generating a migration, and the migration seems to want to migrate basically all DateTime fields from type timestamp without time zone to timestamp with time zone.

Here's an example:

protected override void Up(MigrationBuilder migrationBuilder)
...
            migrationBuilder.AlterColumn<DateTime>(
                name: "CreateTime",
                schema: "wfc",
                table: "Workflow",
                type: "timestamp with time zone",
                nullable: false,
                oldClrType: typeof(DateTime),
                oldType: "timestamp without time zone");
...
}

As linked to in the stacktrace in this issue(See https://aka.ms/efcore-docs-pending-changes.), a behavioral change has happened from EF 8 to 9 where EF will throw an exception when the warning "pending model changes" occurs. Previously it didn't do anything with this warning, but as described in this comment, they changed it to save developers from hard-to-diagnose errors resulting from letting this warning pass.

In Npgsql 6, a breaking change was introduced to the way datetime is mapped in EF(See this changelog). This is likely what triggers the changes I saw in the migration I created for myself as shown above. I see that the last migration was done BEFORE the WorkflowCore.Persistence.PostgreSQL project was upgraded to .NET 6 and started using Npgsql.EntityFrameworkCore.PostgreSQL 6.

I assume from all this that the pending model changes has been there for a while(since this commit), but not blown up because it hasn't been a problem in runtime. The "pending model changes" warning hasn't been an actual error when running trying to migrate programmatically, until .NET 9, so now it blows up.

The release notes of Npsql 6 has a migration guide for these fields, but you can also just use the legacy behavior that was pre Npsql 6(link to how that is done). It does state the following about the migration:

Migrating timestamp columns to timestamptz is a simple procedure, but care must be taken, depending on the current contents of your column.

And

The changes described above are far-reaching, and may break applications in various ways.

And, enabling the AppContext.SetSwitch("Npgsql.EnableLegacyTimestampBehavior", true); for legacy use would probably impact other DbContexts in an application, so perhaps not so straight forward after all.

Hope this information gathering helps, @danielgerlag

Edit:
After a quick glance, it seems the persistence models consistently uses DateTime with Kind set to UTC. Wouldn't this make the migration safe to do after all?