Hydration of root node of match in PE executed from command handlers not working

[James Carnegie]

Doesn't seem to work from Command Handlers in particular:

https://github.com/atomisthq/enrollment-rugs/blob/6bc37a6fa9b4c1bd84163315ab32a305f5028f50/.atomist/handlers/Common.ts#L18

In this example, it's possible to to use the scalar result, but for optional matching, this makes things a bit tricky.

Everything below match.root is undefined, but it should be possible to navigate the graph from this point.

[David Dooling]

Looking at your code,

        const pe = `/members::ChatId()
        [@id='${slackUserId}']/person::Person()
            [/preferences::UserPreferences()]?`;
        const match =
            ctx.pathExpressionEngine.scalar<cortex.ChatTeam, cortex.ChatTeam>(ctx.contextRoot as cortex.ChatTeam, pe);
        // tslint:disable-next-line:no-string-literal
        return new FlowConfig(match.members[0].person["preferences"]);

It seems to me this code would be more likely to succeed:

        const pe = `/members::ChatId()
        [@id='${slackUserId}']/person::Person()
            [/preferences::UserPreferences()]?`;
        const match =
            ctx.pathExpressionEngine.scalar<cortex.ChatTeam, cortex.Person>(ctx.contextRoot as cortex.ChatTeam, pe);
        // tslint:disable-next-line:no-string-literal
        return new FlowConfig(match.preferences);

The matches returned are of the type of the last step in the path expression, Person in this case. But you say your code works, so the match is the ChatTeam?

As for your actual question, we'll have to look into that.