MongoDB $text search with only negated terms

How can the $text query operator be used to find documents not containing a list of forbidden words? The documents don't need to contain anything specific; just none of those words.

This is a pretty common use case, e.g. for profanity filtering, but the MongoDB documentation states, without any explanation or workarounds, that

> When passed a search string that only contains negated words, text search will not match any documents.

Without MongoDB doesn't support this feature, I guess all the solutions will be hack.

And here is mine:

I would create a dummy field to my collection with the same static value, like "dummy":"x". And add this field to the text index. And lastly adding this dummy value x to the query to overcome the limitation of:

> When passed a search string that only contains negated words, text
> search will not match any documents

db.articles.insert(
    [
        { _id: 1, subject: "coffee", dummy: "x" },
        { _id: 2, subject: "Coffee Shopping", dummy: "x" },
        { _id: 3, subject: "Baking a cake", dummy: "x" },
        { _id: 4, subject: "baking", dummy: "x" },
        { _id: 5, subject: "Cafe Con Cake", dummy: "x" },
        { _id: 6, subject: "ice cream", dummy: "x" },
        { _id: 7, subject: "coffee and cream", dummy: "x" }
    ]
)

We are adding dummy field to the text index.

db.articles.createIndex( { subject: "text", dummy:"text" } )

We are adding x to the query:

db.articles.find( { $text: { $search: "x -cream -cake" } } ).projection({"dummy":0})

The result will be like this without the forbidden words cream and cake:

{
	"_id" : 4,
	"subject" : "baking"
},

{
	"_id" : 2,
	"subject" : "Coffee Shopping"
},

{
	"_id" : 1,
	"subject" : "coffee"
}

the $text operator requires at least one inclusive word to match. you can then have as many forbidden words as you like after the inclusion like so:

db.articles.find({
    $text: {
        $search: "coffee -cream -shop"
    }
})

i guess it's a limitation of mongodb's text search engine.

so, the alternative would be to do this:

db.articles.find(
    {
        subject: {
            $not: {
                $in: [/cream/i, /shop/i]
            }
        }
    }
)