Django与另一个字段的多对多关系

Question

我有两个模型，Recipe和Ingredient。食谱模型与成分有许多关系，但我也需要能够指定成分的数量。我的模型目前看起来像：

class Ingredient(models.Model): 
    name = models.CharField(max_length="256", db_index=True, null=True) 

class Recipe(models.Model): 
    ... 
    ingredients = models.ManyToManyField(Ingredient, related_name="RecipeIngredients", db_index=True) 

但显然每个配方将有不同数量的每种成分。所以我需要能够做到这样的事情：

cakeRecipe = Recipe.objects.get(pk=1) 
flour = Ingredient.objects.get(pk=2) 
cakeRecipe.ingredients.add(flour, '200 grams') 

但我不知道如何。任何帮助将不胜感激。谢谢:)

Answer 1

你想要一个中间模型。如同 - 在一些模型中，将使用'through'参数来链接两者。像这样：

class Ingredient(models.Model): 
    name = models.CharField(max_length="256", db_index=True, null=True) 

class Recipe(models.Model): 
    ... 
    ingredients = models.ManyToManyField(Ingredient, 
             related_name="RecipeIngredients", 
             db_index=True, 
             through='Quantity') 


class Quantity(models.Model): 
    ingrediant = models.ForeignKey(Ingredient) 
    recipe = models.ForeignKey(Recipe) 
    amount = models.IntegerField() 
    #... any other fields ... 

了解更多关于它here。

Answer 2

您需要按照上Extra fields on many-to-many relationships说明：

class RecipeIngredient(models.Model): 
    recipe = models.ForeignKey('Recipe') 
    ingredient = models.ForeignKey('Ingredient') 
    quantity = models.CharField(max_length=200) 

class Recipe(models.Model): 
    ingredients = models.ManyToManyField(Ingredient, through=RecipeIngredient)