Unity-Technologies/UnityCsReference · error · ArgumentException

Can't connect a Prefab in the StreamingAssets folder to Game

Error message

Can't connect a Prefab in the StreamingAssets folder to GameObjects in the scene. To save a Prefab to the StreamingAssets folder use SaveAsPrefabAsset instead.

What it means

Thrown by SaveAsPrefabAssetAndConnect when the target assetPath is inside the StreamingAssets folder. StreamingAssets are shipped read-only and cannot be connected to scene instances; connecting requires a standard asset folder. Unity directs the developer to use SaveAsPrefabAsset (without connect) for that location.

Source

Thrown at Editor/Mono/Prefabs/PrefabUtility.cs:2131

        public static GameObject SaveAsPrefabAsset(GameObject instanceRoot, string assetPath)
        {
            bool success;
            return SaveAsPrefabAsset(instanceRoot, assetPath, out success);
        }

        public static GameObject SaveAsPrefabAssetAndConnect(GameObject instanceRoot, string assetPath, InteractionMode action)
        {
            bool success;
            return SaveAsPrefabAssetAndConnect(instanceRoot, assetPath, action, out success);
        }

        public static GameObject SaveAsPrefabAssetAndConnect(GameObject instanceRoot, string assetPath, InteractionMode action, out bool success)
        {
            SaveAsPrefabAssetArgumentCheck(instanceRoot, assetPath, true);

            if (IsPathInStreamingAssets(assetPath))
                throw new ArgumentException("Can't connect a Prefab in the StreamingAssets folder to GameObjects in the scene. To save a Prefab to the StreamingAssets folder use SaveAsPrefabAsset instead.");

            var actionName = "Connect to Prefab";

            if (action == InteractionMode.UserAction)
            {
                Undo.RegisterFullObjectHierarchyUndo(instanceRoot, actionName);
            }

            var assetRoot = SaveAsPrefabAssetAndConnect_Internal(instanceRoot, assetPath, out success);

            if (!success)
            {
                return null;
            }

            if (action == InteractionMode.UserAction)
            {
                Undo.RecordCreatedObject(GetPrefabInstanceHandle(instanceRoot), actionName);

View on GitHub (pinned to 225b0fbdb5)

Solutions

1. Use SaveAsPrefabAsset (no connect) instead of SaveAsPrefabAssetAndConnect for StreamingAssets paths.
2. If you need a connectable Prefab, save it under Assets/ and copy to StreamingAssets separately if runtime streaming is required.
3. Check IsPathInStreamingAssets(assetPath) before deciding which API to call.

Example fix

// before
PrefabUtility.SaveAsPrefabAssetAndConnect(go,
    "Assets/StreamingAssets/x.prefab", InteractionMode.AutomatedAction);
// after
PrefabUtility.SaveAsPrefabAsset(go,
    "Assets/StreamingAssets/x.prefab");

void SavePrefabSmart(GameObject go, string path, bool connect)
{
    bool inStreaming = path.Contains("StreamingAssets");
    if (connect && inStreaming)
    {
        Debug.LogWarning("StreamingAssets path; using SaveAsPrefabAsset.");
        PrefabUtility.SaveAsPrefabAsset(go, path);
    }
    else if (connect)
        PrefabUtility.SaveAsPrefabAssetAndConnect(go, path, InteractionMode.AutomatedAction);
    else
        PrefabUtility.SaveAsPrefabAsset(go, path);
}

static bool IsConnectablePath(string path) =>
    !string.IsNullOrEmpty(path) && !path.Contains("StreamingAssets");

When it happens

Trigger: Calling SaveAsPrefabAssetAndConnect with an assetPath that begins under the project's StreamingAssets directory (IsPathInStreamingAssets returns true).

Common situations: Developer wants to store a Prefab in StreamingAssets for runtime streaming and inadvertently uses the connect variant. Confusion about which StreamingAssets restrictions apply.

Related errors

• Overwriting a folder with an Asset is not allowed: '{path}'
• Saving Prefab to immutable folder is not allowed: '{path}'
• Given path does not exist: '{path}'
• Scene path "{0}" contains invalid directory separators.
• Invalid build path: '{buildPlayerOptions.locationPathName}'.

AI-assisted analysis of Unity-Technologies/UnityCsReference@225b0fbdb5 (2026-08-13). Data as JSON: /api/errors/074568416ea72ac1. Report an issue: GitHub.