dotnet/efcore · error · InvalidOperationException

A synchronous store management operation was performed and…

Error message

A synchronous store management operation was performed and no synchronous seed delegate has been provided, however an asynchronous seed delegate was. Set 'UseSeeding' option with a delegate equivalent to the one supplied in 'UseAsyncSeeding'.

What it means

Thrown from SeedDataAsync when an asynchronous seed delegate was not registered but a synchronous one was, yet the async seeding pipeline is being executed. EF Core requires that when you customize seeding you supply both a sync (UseSeeding) and an async (UseAsyncSeeding) delegate, because both the sync and async store pipelines may run. The error tells you to register the matching delegate.

Solutions

Add a matching UseAsyncSeeding(async (ctx, created, ct) => { ... }) that mirrors the logic in your UseSeeding callback.
Or, if you only ever run async workflows, switch entirely to UseAsyncSeeding and supply a trivial (or no) sync delegate as required by the framework.
Ensure both delegates perform the same seeding work so behavior is identical regardless of which pipeline runs.

Example fix

// before
optionsBuilder.UseSeeding((ctx, created) =>
{
    ctx.Blogs.Add(new Blog { Url = "http://blogs.msdn.com" });
    ctx.SaveChanges();
});

// after
optionsBuilder.UseSeeding((ctx, created) =>
{
    ctx.Blogs.Add(new Blog { Url = "http://blogs.msdn.com" });
    ctx.SaveChanges();
}).UseAsyncSeeding(async (ctx, created, ct) =>
{
    ctx.Blogs.Add(new Blog { Url = "http://blogs.msdn.com" });
    await ctx.SaveChangesAsync(ct);
});

Defensive patterns

Strategy: validation

Validate before calling

// In a startup test, assert both seeders are configured together
var ext = dbContext.Options.FindExtension<CoreOptionsExtension>();
if (ext?.Seeder is not null && ext?.AsyncSeeder is null
    || ext?.Seeder is null && ext?.AsyncSeeder is not null)
{
    throw new InvalidOperationException("Configure UseSeeding AND UseAsyncSeeding together.");
}

Try / catch

try { await dbContext.Database.EnsureCreatedAsync(ct); }
catch (InvalidOperationException ex) when (ex.Message.Contains("UseSeeding"))
{
    // add the missing UseAsyncSeeding (or UseSeeding) delegate, then retry.
}

Prevention

Always register UseSeeding and UseAsyncSeeding as a matched pair.
Add a startup assertion that both (or neither) seeders are configured.
Keep the bodies of both delegates semantically identical.

When it happens

Trigger: Calling DbContextOptionsBuilder.UseSeeding(...) (sync only) without a matching UseAsyncSeeding(...), then invoking the async store-creation pipeline (EnsureCreatedAsync or the internal async SeedDataAsync on CosmosDatabaseCreator). At CosmosDatabaseCreator.cs:252-258, AsyncSeeder is null and Seeder is non-null, so MissingSeeder is thrown.

Common situations: Following an older seeding tutorial that only mentions UseSeeding. Upgrading EF Core to a version that split seeding into sync/async delegates without adding the async overload. ASP.NET Core startup that only configures the sync delegate but the host calls the async path.

Related errors

AI-assisted analysis of dotnet/efcore@3a2006ef56 (2026-08-11). Data as JSON: /api/errors/7a5bef48a24a904c. Report an issue: GitHub.

Appendix: source

Thrown at src/EFCore.Cosmos/Storage/Internal/CosmosDatabaseCreator.cs:258

    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public virtual async Task SeedDataAsync(
        bool created,
        CancellationToken cancellationToken = default)
    {
        var coreOptionsExtension =
            _contextOptions.FindExtension<CoreOptionsExtension>();

        if (coreOptionsExtension?.AsyncSeeder is not null)
        {
            await coreOptionsExtension.AsyncSeeder(_currentContext.Context, created, cancellationToken).ConfigureAwait(false);
        }
        else if (coreOptionsExtension?.Seeder is not null)
        {
            throw new InvalidOperationException(CoreStrings.MissingSeeder);
        }
    }

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>
    public virtual Task<bool> EnsureDeletedAsync(CancellationToken cancellationToken = default)
        => _cosmosClient.DeleteDatabaseAsync(cancellationToken);

    /// <summary>
    ///     This is an internal API that supports the Entity Framework Core infrastructure and not subject to
    ///     the same compatibility standards as public APIs. It may be changed or removed without notice in
    ///     any release. You should only use it directly in your code with extreme caution and knowing that
    ///     doing so can result in application failures when updating to a new Entity Framework Core release.
    /// </summary>

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