使用FOR JSON PATH创建嵌套的JSON数组

Question

我需要从一个查询创建一个JSON输出，该查询使用具有一对多关系的两个表之间的内部连接。 我希望将辅助表的值嵌套为主表的数组属性。

请考虑以下示例：

DECLARE @Persons AS TABLE
(
    person_id int primary key,
    person_name varchar(20)
)

DECLARE @Pets AS TABLE
(
    pet_owner int, -- in real tables, this would be a foreign key
    pet_id int  primary key,
    pet_name varchar(10)
)

INSERT INTO @Persons (person_id, person_name) VALUES
(2, 'Jack'),
(3, 'Jill')

INSERT INTO @Pets (pet_owner, pet_id, pet_name) VALUES
(2, 4, 'Bug'),
(2, 5, 'Feature'),
(3, 6, 'Fiend')

并查询：

DECLARE @Result as varchar(max)
SET @Result =
(
SELECT  person_id as [person.id],
        person_name as [person.name],
        pet_id as [person.pet.id],
        pet_name as [person.pet.name]
FROM @Persons 
JOIN @Pets ON person_id = pet_owner
FOR JSON PATH, ROOT('pet owners')
)

PRINT @Result

这将打印以下JSON：

{
    "pet owners":
    [
    {"person":{"id":2,"name":"Jack","pet":{"id":4,"name":"Bug"}}},
    {"person":{"id":2,"name":"Jack","pet":{"id":5,"name":"Feature"}}},
    {"person":{"id":3,"name":"Jill","pet":{"id":6,"name":"Fiend"}}}
    ]
}

但是，我想将宠物数据作为所有者数据中的数组：

{
    "pet owners":
    [
        {
            "person":
            {
                "id":2,"name":"Jack","pet":
                [
                    {"id":4,"name":"Bug"},
                    {"id":5,"name":"Feature"}
                ]
            }
        },
        {
            "person":
            {
                "id":3,"name":"Jill","pet":
                {"id":6,"name":"Fiend"}
            }
        }
    ]
}

我怎样才能做到这一点？

Answer 1

您可以使用以下查询：

SELECT pr.person_id AS [person.id], pr.person_name AS [person.name],
    (
        SELECT pt.pet_id AS id, pt.pet_name AS name 
        FROM @Pets pt WHERE pt.pet_owner=pr.person_id 
        FOR JSON PATH
    ) AS [person.pet]
FROM @Persons pr 
FOR JSON PATH, ROOT('pet owners')

有关更多信息，请参阅https://blogs.msdn.microsoft.com/sqlserverstorageengine/2015/10/09/returning-child-rows-formatted-as-json-in-sql-server-queries/