生产has_many：production_lines， production_line所属项：项目， has_one项：配方， 配方has_many：recipe_lines， recipe_line归属于：item，
production_line and recipe line have attribute quantity. I need to group recipe_lines for a production by item, with quantity that equals to production_line.quantity * recipe_line.quantity
def item_quantities
array = production_lines.map do |p|
p.item.recipe.recipe_lines.map do |r|
{
item_id: r.item_id,
item_name: r.item.name,
quantity: r.quantity * p.quantity
}
end
end
array.flatten(1).group_by { |p| p[:item_id] }
.transform_values { |vals| vals.sum { |val| val[:quantity] } }
end
返回：
item_quantities = {
1: 10,
2: 5
}
其中key是item_id，value是数量。值是正确的。
但是我想返回：
item_quantities = [
{
id: 1,
name: "Tomato",
quantity: 10,
},
{
id: 2,
name: "Carrot",
quantity: 5
}
]
我应该如何更改解决方案以实现该目标？
First of all, your nested
mapfollowed byflatten(1)can be simplified by making the firstmapintoflat_map. If you do this you could remove theflatten(1).从这一点开始，您的代码已遍历整个过程，但是您可以进行以下更改以获得所需的输出：
you can group by multiple attributes, name and id. In another language you might use a tuple for this. Ruby doesn't have tuples, so we can just use a len-2 array:
At this point you have a hash mapping [id,name] tuple to quantity:
and you can coerce this to the desired data type using
reduce(oreach_with_object, if you prefer):The wierd looking
((id, name), quantity)is a kind of destructuring. See https://jsarbada.wordpress.com/2019/02/05/destructuring-with-ruby/ specifically the sections on "Destructuring Block Arguments" and "Destructuring Hashes".