将 json 转换为嵌套的 postgres 复合类型

Question

我在 postgres 中定义了以下嵌套类型：

CREATE TYPE address AS (
  name    text,
  street  text,
  zip     text,
  city    text,
  country text
);

CREATE TYPE customer AS (
  customer_number           text,
  created                   timestamp WITH TIME ZONE,
  default_billing_address   address,
  default_shipping_address  address
);

现在想在存储过程中填充此类型，该存储过程将 json 作为输入参数。这适用于顶级字段，输出显示了 postgres 复合类型的内部格式：

# select json_populate_record(null::customer, '{"customer_number":"12345678"}'::json)::customer;
 json_populate_record 
----------------------
 (12345678,,,)
(1 row)

但是，postgres 不处理嵌套的 json 结构：

# select json_populate_record(null::customer, '{"customer_number":"12345678","default_shipping_address":{"name":"","street":"","zip":"12345","city":"Berlin","country":"DE"}}'::json)::customer;
ERROR:  malformed record literal: "{"name":"","street":"","zip":"12345","city":"Berlin","country":"DE"}"
DETAIL:  Missing left parenthesis.

再次起作用的是，如果嵌套的属性是 postgres 的内部格式，如下所示：

# select json_populate_record(null::customer, '{"customer_number":"12345678","default_shipping_address":"(\"\",\"\",12345,Berlin,DE)"}'::json)::customer;
            json_populate_record            
--------------------------------------------
 (12345678,,,"("""","""",12345,Berlin,DE)")
(1 row)

有没有办法让 postgres 从嵌套的 json 结构转换为相应的复合类型？

Answer 1

仅对嵌套对象使用json_populate_record()：

with a_table(jdata) as (
values
    ('{
        "customer_number":"12345678",
        "default_shipping_address":{
            "name":"",
            "street":"",
            "zip":"12345",
            "city":"Berlin",
            "country":"DE"
        }
    }'::json)
)
select (
    jdata->>'customer_number', 
    jdata->>'created', 
    json_populate_record(null::address, jdata->'default_billing_address'),
    json_populate_record(null::address, jdata->'default_shipping_address')
    )::customer
from a_table;

                    row                     
--------------------------------------------
 (12345678,,,"("""","""",12345,Berlin,DE)")
(1 row)

嵌套复合类型不是 Postgres（和任何 RDBMS）的设计目标。它们太复杂和麻烦了。在数据库逻辑中，嵌套结构应保持相关 tables，例如

create table addresses (
    address_id serial primary key,
    name text,
    street text,
    zip text,
    city text,
    country text
);

create table customers (
    customer_id serial primary key, -- not necessary `serial` may be `integer` or `bigint`
    customer_number text,           -- maybe redundant
    created timestamp with time zone,
    default_billing_address int references adresses(address_id),
    default_shipping_address int references adresses(address_id)
);

有时在 table 中使用嵌套结构是合理的，但在这些情况下使用 jsonb 或 hstore 似乎更方便和自然，例如：

create table customers (
    customer_id serial primary key, 
    customer_number text,
    created timestamp with time zone,
    default_billing_address jsonb,
    default_shipping_address jsonb
);

Answer 2

plpython 救援：

create function to_customer (object json)
returns customer
AS $$
import json
return json.loads(object)
$$ language plpythonu;

示例：

select to_customer('{
        "customer_number":"12345678",
        "default_shipping_address":
        {
                "name":"",
                "street":"",
                "zip":"12345",
                "city":"Berlin",
                "country":"DE"
        },
        "default_billing_address":null,
        "created": null
}'::json);
                to_customer                 
--------------------------------------------
 (12345678,,,"("""","""",12345,Berlin,DE)")
(1 row)

警告：postgresql 在构建从 python 返回的对象时需要将所有 null 值呈现为 None（即不允许跳过不存在的空值），因此我们必须在传入 json 中指定所有空值。例如，不允许：

select to_customer('{
        "customer_number":"12345678",
        "default_shipping_address":
        {
                "name":"",
                "street":"",
                "zip":"12345",
                "city":"Berlin",
                "country":"DE"
        } 
}'::json);                             
ERROR:  key "created" not found in mapping
HINT:  To return null in a column, add the value None to the mapping with the key named after the column.
CONTEXT:  while creating return value
PL/Python function "to_customer"

Answer 3

这似乎在 Postgres 10 中得到解决。在 release notes 中搜索 json_populate_record 显示以下更改：

Make json_populate_record() and related functions process JSON arrays and objects recursively (Nikita Glukhov)

With this change, array-type fields in the destination SQL type are properly converted from JSON arrays, and composite-type fields are properly converted from JSON objects. Previously, such cases would fail because the text representation of the JSON value would be fed to array_in() or record_in(), and its syntax would not match what those input functions expect.

将 json 转换为嵌套的 postgres 复合类型

Converting json to nested postgres composite type

postgresql

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composite-types