Insert value into JSON array if it is not already present - json

Question

I'm building a bash script that will read the response from an API and insert a value within a [] list (not {} array) if the value isn't present. Fake example response from API:
#response.json contains:
{
"foods": {
"menu": [
"tacos",
"spaghetti",
"pizza",
"chicken_florentine",
"bacon_cheeseburge",
"chow_mein",
"sushi",
"chocolate",
"whiskey"
]
}
}
The variable from my bash script is order="lasagna". If 'foods.menu[]' contains $order then do nothing, else insert $order value into 'foods.menu[]'.
Using bash variable order="lasagna" which currently doesn't exist in 'foods.menu[]', the resulting json should be:
{
"foods": {
"menu": [
"tacos",
"spaghetti",
"pizza",
"chicken_florentine",
"bacon_cheeseburge",
"chow_mein",
"sushi",
"chocolate",
"whiskey",
"lasagna" <----
]
}
}
I started with trying a bash for loop and variations of jq's if-then-else, select, and contains but went down a rabbit hole. Any help is appreciated.

Answer 1

You don't need a loop for that
jq --arg order lasagna '.foods.menu |= if index($order) then . else . + [$order] end' response.json
But you may need one for inserting multiple orders
jq 'reduce $ARGS.positional[] as $order (.;
.foods.menu |= if index($order) then . else . + [$order] end
)' response.json --args apple banana sushi

Answer 2

I don't know if this fits with any unspoken requirements.
Add the item regardless, and then unique the results:
echo "$result" | jq --arg order pizza '.foods.menu |= (. + [$order] | unique)'
{
"foods": {
"menu": [
"bacon_cheeseburge",
"chicken_florentine",
"chocolate",
"chow_mein",
"pizza",
"spaghetti",
"sushi",
"tacos",
"whiskey"
]
}
}
The resulting array is sorted. If there were any duplicates in the input, those are gone.

Answer 3

Here's another way using the alternative operator // to default to the array's length for the item's index:
jq --arg order 'lasagna' '
(.foods.menu | .[index($order) // length]) = $order
' response.json
Adding a list of items in the same manner:
jq '.foods.menu |= reduce $ARGS.positional[] as $order (.;
.[index($order) // length] = $order
)' response.json --args 'lasagna' 'sushi' 'milk'