microsoft/aspire · error · ArgumentException

At least one partition key path should be provided.

Error message

At least one partition key path should be provided.

What it means

AddContainer requires at least one partition key path: the extension materializes the collection to an array and throws ArgumentException when it is empty, mirroring the resource-level validation. Cosmos DB containers cannot be defined without a partition key path.

Solutions

1. Pass at least one non-empty partition key path such as "/id".
2. Validate the collection is non-empty before calling AddContainer.
3. Fix the upstream configuration so at least one path is populated.

Example fix

// before
var paths = config.GetPartitionKeyPaths(); // returns empty list
db.AddContainer("orders", paths);
// after
var paths = config.GetPartitionKeyPaths();
if (paths.Count == 0) throw new InvalidOperationException("At least one partition key path must be configured.");
db.AddContainer("orders", paths);

if (partitionKeyPaths is null || !partitionKeyPaths.Any()) throw new ArgumentException("At least one partition key path must be provided.");

try { db.AddContainer("orders", paths); } catch (ArgumentException ex) when (ex.ParamName == "partitionKeyPaths") { /* fall back to "/id" and retry */ }

When it happens

Trigger: Calling builder.AddContainer(name, Array.Empty<string>()) or an empty List<string>; passing a lazily-evaluated enumerable that yields no items.

Common situations: Building the path list from config where no keys were configured; a LINQ filter that removes all entries before the call; default-initialized empty arrays.

Understand the failure class

Background: "must not be empty", "cannot be empty" — required-field validation errors across open-source libraries — this error's family across 41 libraries.

Related errors

• At least one partition key path should be provided.
• Partition key paths cannot contain null or empty strings.
• At least one terminal host is required.
• Cannot build connection string for MongoDB replica set…
• ConnectionStringAvailableEvent was published for the

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/430263cc8173afd1. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.Azure.CosmosDB/AzureCosmosDBExtensions.cs:443

    /// <summary>
    /// Adds a container to the associated Cosmos DB database resource with hierarchical partition keys.
    /// </summary>
    /// <param name="builder">CosmosDBDatabase resource builder.</param>
    /// <param name="name">Name of container resource.</param>
    /// <param name="partitionKeyPaths">Hierarchical partition key paths for the container.</param>
    /// <param name="containerName">The name of the container. If not provided, this defaults to the same value as <paramref name="name"/>.</param>
    /// <returns>A reference to the <see cref="IResourceBuilder{T}"/>.</returns>
    [AspireExportIgnore(Reason = "Polyglot AppHosts use the internal addContainer dispatcher export.")]
    public static IResourceBuilder<AzureCosmosDBContainerResource> AddContainer(this IResourceBuilder<AzureCosmosDBDatabaseResource> builder, [ResourceName] string name, IEnumerable<string> partitionKeyPaths, string? containerName = null)
    {
        ArgumentNullException.ThrowIfNull(builder);
        ArgumentException.ThrowIfNullOrEmpty(name);
        ArgumentNullException.ThrowIfNull(partitionKeyPaths);
        var partitionKeyPathsArray = partitionKeyPaths.ToArray();
        if (partitionKeyPathsArray.Length == 0)
        {
            throw new ArgumentException("At least one partition key path should be provided.", nameof(partitionKeyPaths));
        }

        if (partitionKeyPathsArray.Any(string.IsNullOrEmpty))
        {
            throw new ArgumentException("Partition key paths cannot contain null or empty strings.", nameof(partitionKeyPaths));
        }

        // Use the resource name as the container name if it's not provided
        containerName ??= name;

        var container = new AzureCosmosDBContainerResource(name, containerName, partitionKeyPaths, builder.Resource);

        builder.Resource.Containers.Add(container);

        return builder.ApplicationBuilder.AddResource(container)
            .WithIconName("Box");
    }

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