JosefNemec/Playnite · error · Exception

Can't assign object to uknown dat property.

Error message

Can't assign object to uknown dat property.

What it means

Thrown by DatParser when a top-level DAT property name matches a known datGameProperties key, but its value is a nested DatObject rather than a scalar string. Only a few keys (like 'rom') are handled as nested objects; any other key whose value is an object has no target mapping and the parser refuses to guess, raising a generic Exception. Note the misspelling 'uknown' is intentional/consistent with the codebase.

Source

Thrown at source/Tools/Playnite.Utilities/DatParser.cs:94

            foreach (var prop in datObj.Properties)
            {
                var romAdded = false;
                if (prop.Name == "rom" && !romAdded)
                {
                    romAdded = true;
                    foreach (var romDatProp in (prop.Value as DatObject).Properties)
                    {
                        if (datGameProperties.TryGetValue("rom." + romDatProp.Name, out var romPropInfo))
                        {
                            SetParsedProperty(romPropInfo, datGame, (string)romDatProp.Value);
                        }
                    }
                }
                else if (datGameProperties.TryGetValue(prop.Name, out var propInfo))
                {
                    if (prop.Value is DatObject)
                    {
                        throw new Exception("Can't assign object to uknown dat property.");
                    }

                    SetParsedProperty(propInfo, datGame, (string)prop.Value);
                }
            }

            datGame.FixData();
            return datGame;
        }

        private void SetParsedProperty(PropertyInfo prop, object datGame, string propValue)
        {
            if (prop.PropertyType == typeof(uint))
            {
                prop.SetValue(datGame, uint.Parse(propValue));
            }
            else if (prop.PropertyType == typeof(int))
            {

View on GitHub (pinned to 5911f4e964)

Solutions

1. Inspect the offending DAT entry to find which property name carries an object value instead of a string.
2. If the nested object is legitimate, add an explicit branch in the parser (mirroring the 'rom' handling) to map its sub-properties before this else-if falls through.
3. Pre-process/sanitize the DAT so recognized keys carry scalar values.
4. Report the property name upstream so the DAT schema can be corrected.

Example fix

// before
else if (datGameProperties.TryGetValue(prop.Name, out var propInfo))
{
    if (prop.Value is DatObject)
        throw new Exception("Can't assign object to uknown dat property.");
    SetParsedProperty(propInfo, datGame, (string)prop.Value);
}

// after (handle a legitimate nested container explicitly)
else if (prop.Name == "custom" && prop.Value is DatObject custom)
{
    foreach (var sub in custom.Properties)
        if (datGameProperties.TryGetValue("custom." + sub.Name, out var sp))
            SetParsedProperty(sp, datGame, (string)sub.Value);
}
else if (datGameProperties.TryGetValue(prop.Name, out var propInfo))
{
    SetParsedProperty(propInfo, datGame, (string)prop.Value);
}

static bool IsKnownScalarProperty(string name, object value) =>
    datGameProperties.ContainsKey(name) && !(value is DatObject);

// guard before assignment:
if (prop.Value is DatObject obj)
    logger.Warn($"Skipping nested object on known property '{prop.Name}' — no mapping.");
else
    SetParsedProperty(propInfo, datGame, (string)prop.Value);

When it happens

Trigger: Parsing a .dat file whose structure nests an object under a property name that is recognized but not the 'rom' container — i.e. a DAT object whose Name collides with a flat datGame property but whose Value is itself a DatObject.

Common situations: Custom or non-standard DAT exports that nest data unexpectedly; a DAT from a different emulator/curation tool using object values for fields Playnite expects as scalars; schema drift in an upstream DAT generator.

Related errors

• URL file doesn't have shortcut definition section.
• playnite:// uri missing parameters.

AI-assisted analysis of JosefNemec/Playnite@5911f4e964 (2026-08-13). Data as JSON: /api/errors/02dd3d957ed7e345. Report an issue: GitHub.