microsoft/aspire · error · DistributedApplicationException

Project metadata was not found for resource

Error message

Project metadata was not found for resource '{project.Name}'.

What it means

During manifest publishing, ManifestPublishingContext.WriteProjectAsync serializes a ProjectResource, but every project resource must carry IProjectMetadata (its project file path). If the resource is a ProjectResource without that metadata annotation, Aspire cannot emit a valid manifest entry, so it throws DistributedApplicationException. This is an internal model invariant: only AddProject creates valid project resources.

Solutions

Use IDistributedApplicationBuilder.AddProject<TProject>(name) instead of manually constructing ProjectResource so IProjectMetadata is attached automatically.
If building a custom resource, ensure TryGetProjectMetadata succeeds by annotating the resource with IProjectMetadata (project path resolved via PhysicalFile path of the .csproj).
Check custom model transforms/annotations that may remove project metadata before publishing.

Example fix

// before
var project = new ProjectResource("api");
builder.AddResource(project);
// after
builder.AddProject<Projects.Api>("api");

Defensive patterns

Strategy: validation

Validate before calling

if (!project.TryGetProjectMetadata(out var metadata))
{
    throw new InvalidOperationException($"Resource '{project.Name}' is a ProjectResource without project metadata; use AddProject<T>.");
}

Type guard

static bool HasProjectMetadata(ProjectResource p) => p.TryGetProjectMetadata(out _);

Prevention

Always create project resources via AddProject<TProject>.
Never construct ProjectResource manually in production code.
Review custom model transforms for annotation removal.

When it happens

Trigger: Calling AddResource (or building a custom resource derived from ProjectResource) with a ProjectResource constructed manually that never received IProjectMetadata, instead of using builder.AddProject; or removing/replacing the metadata annotation before publish runs.

Common situations: Custom resource-building helpers that new up ProjectResource directly; tests or tools that manipulate the distributed application model and strip annotations; upgrading custom code after the ProjectResource/metadata API changed.

Understand the failure class

Background: 'Could not be found', 'does not exist', 'not found in database': the resource-not-found family when an ID, slug, key, or URI lookup comes back empty — this error's family across 20 libraries.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/196912c8d4270dc9. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting/Publishing/ManifestPublishingContext.cs:179

    {
        Writer.WriteString("error", "This resource does not support generation in the manifest.");
        return Task.CompletedTask;
    }

    private Task WriteConnectionStringAsync(IResourceWithConnectionString resource)
    {
        // Write connection strings as value.v0
        Writer.WriteString("type", "value.v0");
        WriteConnectionString(resource);

        return Task.CompletedTask;
    }

    private async Task WriteProjectAsync(ProjectResource project)
    {
        if (!project.TryGetProjectMetadata(out var metadata))
        {
            throw new DistributedApplicationException($"Project metadata was not found for resource '{project.Name}'.");
        }

        var relativePathToProjectFile = GetManifestRelativePath(metadata.ProjectPath);

        var deploymentTarget = project.GetDeploymentTargetAnnotation();
        if (deploymentTarget is not null)
        {
            Writer.WriteString("type", "project.v1");
        }
        else
        {
            Writer.WriteString("type", "project.v0");
        }

        Writer.WriteString("path", relativePathToProjectFile);

        if (deploymentTarget is not null)
        {

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