如何獲取未保存在數據庫中的對象的ID？

Question

我在Cart模型的方法：

def add_product_with_variant(product_id, variant_id) 
    current_item = line_items.find_by(product_id: product_id) 
    if current_item 
    current_item.amount += 1 
    line_item_variant = LineItemVariant.new(variant_id: variant_id, line_item_id: current_item.id) 
    line_item_variant.save 
    else 
    current_item = line_items.build(product_id: product_id) 
    line_item_variant = LineItemVariant.new(variant_id: variant_id, line_item_id: current_item.id) 
    line_item_variant.save! 
    end 
end 

在else發言中，我使用LineItemvariant.new(variant_id: variant_id, line_item_id: current_item.id)到variant分配給line_item。但在這種情況下，我不能保存LineItemVariant，因爲line_item尚不存在，我不能使用這部分代碼：line_item_id: current_item.id。有沒有解決方案來獲得ID，或者有更簡單的方法來解決這個問題？謝謝你。

Answer 1

您可以使用accepts_nested_attributes_for

裏面你LineItemVariant模型定義

accepts_nested_attributes_for :line_item # or whatever relation is towards this item 

，然後改變你的else語句

嘗試對象轉換成JSON傳遞時使用to_json

def add_product_with_variant(product_id, variant_id) 
    current_item = line_items.find_by(product_id: product_id) 
    if current_item 
    current_item.amount += 1 
    line_item_variant = LineItemVariant.new(variant_id: variant_id, line_item_id: current_item.id) 
    line_item_variant.save 
    else 
    current_item = line_items.build(product_id: product_id) 
    line_item_variant = LineItemVariant.new(variant_id: variant_id, line_item: current_item.to_json) 
    line_item_variant.save! 
end