使用 Ecto.Query 的递归 SQL 查询

Question

我有一个 categories table 包含以下列：

id
name
parent_id (nullable)

还有一个 books table，里面有一个 category_id 列。我想要一个函数，它接受类别 ID 列表 (category_ids) 和 returns 一个查询，该查询获取属于给定类别之一或其子类别的书籍（递归）。

我已经编写了一个 returns 给定类别的所有子项的查询。我可以使用它来获取 category_ids 类别的所有子类别并使用新列表。但它会向数据库发送多个查询，我想在一个查询中完成。这是查询：

with recursive cat_tree as (
  select id,
    name,
    parent_id
  from categories
  where id = 
  union all
  select child.id, 
    child.name,
    child.parent_id
  from categories as child
  join cat_tree as parent on parent.id = child.parent_id
)
select *
from cat_tree;

已编辑

  @raw_sql """
  select id,
    name,
    parent_id
  from categories
  where id in (?)
  union all
    select child.id,
           child.name,
           child.parent_id
  from categories as child
    join cat_tree as parent on parent.id = child.parent_id
  """

  def category_search_query(query, []), do: query 
  def category_search_query(query, category_ids) do
    query
    |> recursive_ctes(true)
    |> with_cte("cat_tree", as: fragment(@raw_sql, ^category_ids))
    |> join(:inner, [b], c in "cat_tree", on: c.id == b.category_id)
  end

但是当我将 [12, 13]（例如）传递给函数时，它会出现以下错误：

(DBConnection.EncodeError) Postgrex expected an integer in -9223372036854775808..9223372036854775807, got '\f\r'. Please make sure the value you are passing matches the definition in your table or in your query or convert the value accordingly.

但是当我只传递一个整数（而不是列表）时，它工作正常。

Answer 1

我会制作一个程序来获取类别列表作为参数（可以是数组）并将您的查询更改为：

create function funcName (categoryIds int[])
returns table ( bookid int ,categoryid int , ...<deffine book columns>)
as 
$$ 
with recursive cat_tree as (
    select
        id,name,parent_id
    from
        categories
    where id in (select unnest(categoryIds))
    union all
    select
        child.id,child.name,child.parent_id
    from
        categories as child
    join cat_tree as parent on parent.id = child.parent_id
)
select
    b.*
from
    cat_tree c
join books on c.id = b.categoryid
$$ Language sql;

使用 Ecto.Query 的递归 SQL 查询

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