mysql - 如何处理链接同一实体的多个列

Question

这个例子只是我的数据库的一个模式。我有下表称为食谱:

id | author_name | recipe1_id | recipe2_id | recipe3_id

所有食谱都与 recipes_ingredients 表有关:

id | recipe_id | ingredient1 | ingredient2 | ingredient3

现在我在 recipe1_id 到 recipe3_id 上做了三个 JOINS，如下所示:

SELECT recipe1.ingredient1 as recipe1ingredient1, recipe1.ingredient2 as recipe1ingredient2, recipe1.ingredient3 as recipe1ingredient3, [...]
FROM recipes
INNER JOIN recipe recipe1 ON (recipes.recipe1_id = recipes.id)
INNER JOIN recipe recipe2 ON (recipes.recipe2_id = recipes.id)
INNER JOIN recipe recipe3 ON (recipes.recipe3_id = recipes.id)

为了将 3 个食谱映射到 MyBatis 中的一个 bean，我有三个 resultsMap，它们将每个食谱映射到一个包含 3 种成分的食谱对象(recipe1、recipe2、recipe3)。

但是:我想将食谱列在一个列表中。我怎样才能做到这一点？

PS:可以肯定的是，我在表 recipes 和表 recipes_ingredients 中只有 3 个实体。这永远不会改变，所以我看不出有什么理由将它放在 n:m 表中。

Answer 1

我认为这会奏效。

<resultMap id="recipe1" type="recipe1">
 ...
</resultMap>

<resultMap id="recipe2" type="recipe2">
 ...
</resultMap>

<resultMap id="recipe3" type="recipe3">
 ...
</resultMap>

<select id="getRecipes" parameterType="list" resultMap="recipe1, recipe2, recipe3">
   SELECT recipe1.ingredient1 as recipe1ingredient1, recipe1.ingredient2 as recipe1ingredient2, recipe1.ingredient3 as recipe1ingredient3, [...]
   FROM recipes
   INNER JOIN recipe recipe1 ON (recipes.recipe1_id = recipes.id)
   INNER JOIN recipe recipe2 ON (recipes.recipe2_id = recipes.id)
   INNER JOIN recipe recipe3 ON (recipes.recipe3_id = recipes.id)
</select>

来源:MyBatis multiple resultsets