microsoft/aspire · error · InvalidOperationException

A DbContext could not be configured with this…

Error message

A DbContext could not be configured with this AddCosmosDbContext overload. Ensure the connection string '{connectionName}' contains a database name or use the overload that takes a database name as a parameter.

What it means

The parameterless AddCosmosDbContext overload infers the database name from the connection string; when parsing yields no database name, EF Core cannot be wired to Cosmos and the extension throws. This overload contract requires 'Database=' in the connection string, otherwise the overload accepting a databaseName parameter must be used.

Solutions

Add 'Database=<name>' to the connection string.
Or switch to the AddCosmosDbContext<TContext>(builder, connectionName, databaseName) overload.
Or set the database name in the 'Aspire:Microsoft:EntityFrameworkCore:Cosmos' configuration section if supported by that path.

Example fix

// before
builder.AddCosmosDbContext<OrderContext>("cosmosdb"); // no Database= in string
// after
builder.AddCosmosDbContext<OrderContext>("cosmosdb", "orders-db");

Defensive patterns

Strategy: validation

Validate before calling

// before AddCosmosDbContext without a databaseName parameter
var cs = builder.Configuration.GetConnectionString(connectionName);
if (cs is not null && !cs.Contains("Database="))
{
    throw new InvalidOperationException("Use the AddCosmosDbContext overload with an explicit database name.");
}

Type guard

bool ConnectionStringHasDatabase(string? cs) => cs?.Split(';').Any(p => p.TrimStart().StartsWith("Database=", StringComparison.OrdinalIgnoreCase)) == true;

Try / catch

try { builder.AddCosmosDbContext<OrderContext>("cosmosdb"); }
catch (InvalidOperationException ex) when (ex.Message.Contains("AddCosmosDbContext overload")) { builder.AddCosmosDbContext<OrderContext>("cosmosdb", "orders-db"); }

Prevention

Prefer the explicit databaseName overload; it makes intent obvious and config-independent.
Keep Database= in connection strings when using the inferred overload.
Review connection strings when regenerating them from tooling or CI secrets.

When it happens

Trigger: builder.AddCosmosDbContext<MyContext>(connectionName) where the connection string in 'ConnectionStrings:{connectionName}' has no 'Database=' key and no databaseName parameter overload was used.

Common situations: Connection string contains only endpoint + key; developer swapped from the named-database overload to the inferred one during refactoring; config value regenerated by tooling dropped the Database attribute.

Understand the failure class

Background: "missing required argument" and "the following required arguments were not provided": what required-argument errors mean and how to fix them — this error's family across 20 libraries.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/fa19fd58bab2fe6f. Report an issue: GitHub.

Appendix: source

Thrown at src/Components/Aspire.Microsoft.EntityFrameworkCore.Cosmos/AspireAzureEFCoreCosmosExtensions.cs:54

    public static void AddCosmosDbContext<[DynamicallyAccessedMembers(RequiredByEF)] TContext>(
        this IHostApplicationBuilder builder,
        string connectionName,
        Action<EntityFrameworkCoreCosmosSettings>? configureSettings = null,
        Action<DbContextOptionsBuilder>? configureDbContextOptions = null) where TContext : DbContext
    {
        ArgumentNullException.ThrowIfNull(builder);
        ArgumentException.ThrowIfNullOrEmpty(connectionName);

        string? databaseName = null;
        if (builder.Configuration.GetConnectionString(connectionName) is string connectionString)
        {
            var cosmosConnectionInfo = CosmosUtils.ParseConnectionString(connectionString);
            databaseName = cosmosConnectionInfo.DatabaseName;
        }

        if (databaseName is null)
        {
            throw new InvalidOperationException(
                "A DbContext could not be configured with this AddCosmosDbContext overload. "
                + $"Ensure the connection string '{connectionName}' contains a database name or use the overload that takes a database name as a parameter.");
        }

        AddCosmosDbContext<TContext>(
            builder,
            connectionName,
            databaseName,
            configureSettings,
            configureDbContextOptions);
    }

    /// <summary>
    /// Registers the given <see cref="DbContext" /> as a service in the services provided by the <paramref name="builder"/>.
    /// Enables db context pooling, logging and telemetry.
    /// </summary>
    /// <typeparam name="TContext">The <see cref="DbContext" /> that needs to be registered.</typeparam>
    /// <param name="builder">The <see cref="IHostApplicationBuilder" /> to read config from and add services to.</param>

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