煎饼大师：寻找缺失的食谱配料

假设你有一个包含食谱和配料的数据库，以及厨师及其当前的厨房存货。

一位厨师（被同事们敬佩并仅称为“煎饼大师”）想做一些煎饼。在开始之前，他需要知道厨房里是否有合适的配料。

我们首先创建配料。

MERGE (:Ingredient {name: "Flour"})
MERGE (:Ingredient {name: "Baking Powder"})
MERGE (:Ingredient {name: "Salt"})
MERGE (:Ingredient {name: "Sugar"})
MERGE (:Ingredient {name: "Egg"})
MERGE (:Ingredient {name: "Milk"})
MERGE (:Ingredient {name: "Butter"});

我们也描述了一个好的煎饼食谱。

MERGE (flour:Ingredient {name: "Flour"})
MERGE (powder:Ingredient {name: "Baking Powder"})
MERGE (salt:Ingredient {name: "Salt"})
MERGE (sugar:Ingredient {name: "Sugar"})
MERGE (egg:Ingredient {name: "Egg"})
MERGE (milk:Ingredient {name: "Milk"})
MERGE (butter:Ingredient {name: "Butter"})
CREATE (pancake:Recipe {title: "Ultimate Pancake Recipe"})
CREATE (pancake)-[:requires_value]->(flour_val:Value)-[:is_part_of]->(flour)
CREATE (pancake)-[:requires_value]->(powder_val:Value)-[:is_part_of]->(powder)
CREATE (pancake)-[:requires_value]->(salt_val:Value {value: "Himalaya"})-[:is_part_of]->(salt)
CREATE (pancake)-[:requires_value]->(sugar_val:Value {value: "White"})-[:is_part_of]->(sugar)
CREATE (pancake)-[:requires_value]->(egg_val:Value {value: "Bio"})-[:is_part_of]->(egg)
CREATE (pancake)-[:requires_value]->(milk_val:Value {value: "Bio"})-[:is_part_of]->(milk)
CREATE (pancake)-[:requires_value]->(butter_val:Value {value: "Plain"})-[:is_part_of]->(butter)
RETURN *;

嗯，煎饼，美味！

接下来，让我们描述一下煎饼大师厨房里还剩下什么

CREATE (pancakeMaster:Chef {name: "Master of Pancakes"})
MERGE (flour:Ingredient {name: "Flour"})
MERGE (salt:Ingredient {name: "Salt"})
MERGE (sugar:Ingredient {name: "Sugar"})
MERGE (egg:Ingredient {name: "Egg"})
MERGE (milk:Ingredient {name: "Milk"})
MERGE (butter:Ingredient {name: "Butter"})
CREATE (pancakeMaster)-[:has_value]->(flour_val:Value)-[:is_part_of]->(flour)
CREATE (pancakeMaster)-[:has_value]->(salt_val:Value {value: "Fleur de Sel"})-[:is_part_of]->(salt)
CREATE (pancakeMaster)-[:has_value]->(sugar_val:Value {value: "Brown"})-[:is_part_of]->(sugar)
CREATE (pancakeMaster)-[:has_value]->(egg_val:Value {value: "Bio"})-[:is_part_of]->(egg)
CREATE (pancakeMaster)-[:has_value]->(milk_val:Value {value: "Bio"})-[:is_part_of]->(milk)
CREATE (pancakeMaster)-[:has_value]->(butter_val:Value {value: "Salty"})-[:is_part_of]->(butter)
RETURN *;

现在，我们有了所有数据，让我们看看是否准备好做煎饼了

MATCH
  (pancake:Recipe {title: "Ultimate Pancake Recipe"})-[:requires_value]->(req_value:Value)-[:is_part_of]->(ingredient:Ingredient)
OPTIONAL MATCH (ingredient)<-[:is_part_of]-(avail_value)<-[:has_value]-(pancakeMaster:Chef {name: "Master of Pancakes"})
RETURN ingredient.name AS ingredient, req_value, avail_value;

这已经不错了，但我们只想看到缺失的配料或种类不正确的配料。为此，我们需要比较所需的配料和现有的配料

MATCH
  (pancake:Recipe {title: "Ultimate Pancake Recipe"})-[:requires_value]->(req_value:Value)-[:is_part_of]->(ingredient:Ingredient)
OPTIONAL MATCH (ingredient)<-[:is_part_of]-(avail_value)<-[:has_value]-(pancakeMaster:Chef {name: "Master of Pancakes"})
WITH ingredient, req_value, avail_value
WHERE avail_value IS NULL OR req_value.value <> avail_value.value
RETURN
  ingredient.name AS ingredient,
  CASE WHEN req_value.value IS NULL THEN "Any" ELSE req_value.value END AS required,
  CASE WHEN avail_value IS NULL THEN "None" ELSE avail_value.value END AS available;

呀！咸黄油！如果我们能弄到一些泡打粉和非咸黄油，我们就可以开始做了。

MERGE (pancakeMaster:Chef {name: "Master of Pancakes"})
MERGE (powder:Ingredient {name: "Baking Powder"})
MERGE (butter:Ingredient {name: "Butter"})
WITH *
MATCH (pancakeMaster)-[:has_value]->(butter_val:Value)-[:is_part_of]->(butter)
SET butter_val.value = "Plain"
CREATE (pancakeMaster)-[:has_value]->(powder_val:Value)-[:is_part_of]->(powder)
RETURN *;

瞧，现在厨师可以开始施展他的魔力了

MATCH (pancake:Recipe {title: "Ultimate Pancake Recipe"})-[:requires_value]->(req_value:Value)-[:is_part_of]->(ingredient:Ingredient)
OPTIONAL MATCH (ingredient)<-[:is_part_of]-(avail_value)<-[:has_value]-(pancakeMaster:Chef {name: "Master of Pancakes"})
WITH ingredient, req_value, avail_value
WHERE avail_value IS NULL OR req_value.value <> avail_value.value
RETURN
  ingredient.name AS ingredient,
  CASE WHEN req_value.value IS NULL THEN "Any" ELSE req_value.value END AS required,
  CASE WHEN avail_value IS NULL THEN "None" ELSE avail_value.value END AS available;

正如你所见，用 Neo4j 烹饪非常有趣！

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煎饼大师：寻找缺失的食谱配料