Dialogflow: How to store multiple parameters in a list parameter from different user sentences?

Basically I want to achieve this:

1.user: I want apple.
bot: You want apple right? 
2.user: I also want banana.
bot: You want apple and banana right? 

Here apple and banana are all parameters of the same fruit entity. In my webook backend I want to receive [apple, banana] when the user entered 2nd sentence, so the bot needs to remember all the fruit (parameters) users gave during the conversation.

I was playing around with dialogflow context. I know it could pass parameters between different intents. But at here I'm using the same intent buyFruit, so the output context only has the new fruit parameters user entered in a new sentence:

1.user: I want apple. -> outputContext.parameters = [apple]
2.user: I also want banana. -> outputContext.parameters = [banana]

I couldn't find a way to get the fruit parameters user said in previous sentences. In another word, I want outputContext.parameters = [apple, banana] in the second webhook request. Does anyone know how to achieve this?

I found the solution to this. I will assume you understand how to use fulfillment, and adding webhooks. If not, feel free to visit here or shoot a question.

For this, there are 3 necessary parts. Dialogflow, your fulfillment code ( I used flask and python), and communication between the two. Enable Webhook, fill in the appropriate local machine url (for this I used NGROK).

I created a cart and a function for creating and maintaining said cart. Below is the code:

from flask import Flask, request

app = Flask(__name__)



##Create the cart
cart = []


#create a route for the webhook
@app.route('/webhook', methods=['GET', 'POST'])
def webhook():
    req = request.get_json(silent=True, force=True)
    fulfillmentText = ''
    query_result = req.get('queryResult')

    if query_result.get('action') == 'order.wings':
        food_data = query_result['parameters']

        ##create temp dictionary so we always extract correct order data
        temp_dictionary = []
        for item in food_data:
            temp_dictionary.append(item)

        ##add items to cart
        new_item = []
        for item in temp_dictionary:
            new_item.append(food_data[item])

        cart.append(new_item)
        print(cart)


        fulfillmentText = "Added Wings to Cart"
    return {
            "fulfillmentText": fulfillmentText,
            "source": "webhookdata"
    }


#run the app
if __name__ == '__main__':
    app.run()