[davvid]

Here's the equivalent using jsonaxe[1]. The main difference is the python-like syntax, which is either good or bad depending on your tastes. The pain point about string interpolation remains, tho.

    data=input.json
    
    fruits () {
        jsonaxe 'models.filter(lambda x: x["title"] == "fruits")[0]' "$data"
    }
    
    farmers () {
        jsonaxe 'models.filter(lambda x: x["title"] == "farmers")[0]' "$data"
    }
    
    fruit_name_key=$(fruits |
        jsonaxe --raw 'fields.filter(lambda x: x["name"] == "Name")[0].key')
    
    farmer_name_key=$(farmers |
        jsonaxe --raw 'fields.filter(lambda x: x["name"] == "Full name")[0].key')
    
    farmer_fruits_key=$(farmers |
        jsonaxe --raw 'fields.filter(lambda x: x["name"] == "Fruits")[0].key')
    
    farmers |
    # get bob
    jsonaxe "entities.filter(lambda x: x['$farmer_name_key'] == 'Bob, the farmer')[0]" |
    # get bob's fruits key
    jsonaxe --raw "get('$farmer_fruits_key')" |
    while read fruit_id
    do
        fruits |
        jsonaxe "entities.filter(lambda x: x['_id'] == '$fruit_id')[0]" |
        jsonaxe "get('$fruit_name_key')"
    done

[1] https://github.com/davvid/jsonaxe