Nested object count

gistfile1.txt

What do I need?
    Retrieve all buckets which have at least 2 different products. In the example below, the query would return buckets 1 and 3.
    Note: I need 2 different product names (p1 and p2) not product quantity (2x p1 or 2x p2)


My mapping definition for a bucket (product is a nested type, mapped automatically by Elasticsearch):
mappings:{
    bucket:{
        properties:{
            id:{type:number},
            ...
            products: {
                properties: {
                    product_name:{ type: string},
                    has_discount:{type: boolean},   
                    quantity: {type:long}
                }  
            }
        }
    }
}
  

Search response example:
 -XGET localhost:9200/orders/bucket/_search:

[
	{	"_type": bucket
		"_source":{
		    id:1
			...
			products:[
				{
                    product: "p1",
                    has_discount: true,
                    quantity: 2
                }
				{
                    product: "p2",
                    has_discount: false,
                    quantity: 1
                }
				{
                    product: "p3",
                    has_discount: true,
                    quantity: 1
                }
			]
		}
	},
	{	"_type": bucket
		"_source":{
		    id:2
			...
			products:[
				{
                    product: "p1",
                    has_discount: false,
                    quantity: 3
                }
			]
		}
	},
	{	"_type": bucket
		"_source":{
		    id:3
			...
			products:[
				{
                    product: "p2",
                    has_discount: true,
                    quantity: 2
                }
				{
                    product: "p3",
                    has_discount: false,
                    quantity: 1
                }
			]
		}
	}
]