FOR JSON PATHを使用してネストされたJSON配列を作成する
1対多の関係を持つ2つのテーブル間の内部結合を使用するクエリからJSON出力を作成する必要があります。
セカンダリテーブルの値をプライマリテーブルの配列プロパティとしてネストしたい。
次の例を考えてみます。
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')
そしてクエリ：
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
これにより、次のJSONが出力されます。
{
"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"}}}
]
}
ただし、飼い主データ内の配列としてペットデータを使用したいと思います。
{
"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"}
}
}
]
}
これどうやってするの？
次のクエリを使用できます。
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')
深くネストされた配列では、サブクエリはすぐに管理できなくなります。
select id,foo, (select id, bar, (select ... for json path) things,
(select...) more_things) yet_more, select(...) blarg
for json pathと同様に、すべてのテーブルを結合し、列のエイリアスにjson構造が埋め込まれたリレーショナル（非json）ビューを作成します。しかし、jsonノードが配列であることを示す[]もあります。このような：
select p.id [id], p.foo [foo], c.name [children[].name], c.id [children[].id],
gp.name [grandparent.name], gc.name [children[].grandchildren[].name]
from parent p
join children c on c.parent_id = p.id .....
リレーショナルビューの列名を解析してjsonをきれいにするjsonビューを非jsonビューに作成するストアドプロシージャを作成しました。下記参照。リレーショナルビューの名前を付けて呼び出すと、ビューが作成されます。完全にはテストされていませんが、私にとってはうまくいきます。ただし、テーブルにはidと呼ばれる列が必要ですid。string_agg（）とjson_array（）を使用しますsqlのバージョンはかなり新しいものである必要があります。また、ルートに配列を返すように設定されています。オブジェクトを返すには微調整が必要です。
create procedure create_json_from_view
@view_name varchar(max)
as
create table #doc_schema (
node_level int, -- nesting level starting with 0
node_name varchar(max), -- alias used for this nodes query
node_path varchar(max), -- full path to this node
parent_path varchar(max), -- full path to it's parents
is_array bit, -- is node marked as array by ending with []
select_columns varchar(max),-- comma separated path/alias pairs for selected columns on node
group_by_columns varchar(max), -- comma separated paths for selected columns on node. group by is necessary to prevent duplicates
node_parent_id varchar(max), -- the id column path to join subquery to parent. NOTE: ID COLUMN MUST BE CALLED ID
from_clause varchar(max), -- from clause built from above fields
node_query varchar(max) -- complete query built from above fields
)
/* get each node path from view schema
*/
INSERT INTO #doc_schema (node_path)
select distinct LEFT(COLUMN_NAME,CHARINDEX('.'+ VALUE + '.',COLUMN_NAME) + LEN(VALUE)) node_path
FROM INFORMATION_SCHEMA.COLUMNS
CROSS APPLY STRING_SPLIT(COLUMN_NAME, '.')
WHERE CHARINDEX('.',COLUMN_NAME) > 0
AND RIGHT(COLUMN_NAME,LEN(VALUE)) <> VALUE
and table_name = @view_name
/* node_name past rightmost period or the same as node_path if there is no period
also remove [] from arrays
*/
update #doc_schema set node_name =
case when charindex('.',node_path) = 0 then replace(node_path,'[]','')
else REPLACE(right(node_path,charindex('.',reverse(node_path)) - 1),'[]','') end
/* if path ends with [] node is array
escapes are necessary because [] have meaning for like
*/
update #doc_schema set is_array =
case when node_path like '%\[\]' escape '\' then 1 else 0 end --\
/* parent path is everything before last . in node path
except when the parent is the root, in which case parent is empty string
*/
update #doc_schema set parent_path =
case when charindex('.',node_path) = 0 then ''
else left(node_path,len(node_path) - charindex('.',reverse(node_path))) end
/* level is how many . in path. an ugly way to count.
*/
update #doc_schema set node_level = len(node_path) - len(replace(node_path,'.','')) + 1
/* set up root node
*/
insert into #doc_schema (node_path,node_name,parent_path,node_level,is_array)
select '','',null,0,1
/* I'm sorry this is so ugly. I just gave up on explaining
all paths need to be wrapped in [] and internal ] need to be escaped as ]]
*/
update #doc_schema set select_columns = sub2.select_columns, group_by_columns = sub2.group_by_columns
from (
select node_path,string_agg(column_path + ' ' + column_name,',') select_columns,
string_agg(column_path,',') group_by_columns
from (
select ds.node_path,'['+replace(c.COLUMN_NAME,']',']]')+']' column_path,replace(c.column_name,ds.node_path + '.','') column_name
from INFORMATION_SCHEMA.COLUMNS c
join #doc_schema ds
on (charindex(ds.node_path + '.', c.COLUMN_NAME) = 1
and charindex('.',replace(c.COLUMN_NAME,ds.node_path + '.','')) = 0)
or (ds.node_level = 0 and charindex('.',c.COLUMN_NAME) = 0)
where table_name = @view_name
) sub
group by node_path
) sub2
where #doc_schema.node_path = sub2.node_path
/* id paths for joining subqueries to parents
Again, the need to be wrapped in [] and and internal ] need to be escaped as ]]
*/
update #doc_schema set node_parent_id =
case when parent_path = '' then '[id]'
else '[' + replace(parent_path,']',']]')+'.id]'
end
/* table aliases for joining subqueries to parents need to be unique
just use L0 L1 etc based on nesting level
*/
update #doc_schema set from_clause =
case when node_level = 0 then ' from ' + @view_name + ' L'+cast(node_level as varchar(4)) + ' '
else ' from ' + @view_name + ' L'+cast(node_level as varchar(4))+' where L'+cast(node_level - 1 as varchar(4))+'.'+ node_parent_id +
' = L'+cast(node_level as varchar(4))+'.'+ node_parent_id
end
/* Assemble node query from all parts
###subqueries### is a place to put subqueries for node
*/
update #doc_schema set node_query =
' (select ' + select_columns + ', ###subqueries###' + from_clause
+ ' group by '+ group_by_columns
+' for json path) '
/* json path will treat all objects as arrays so select first explicitly
to prevent [] in json
*/
update #doc_schema set node_query =
case when is_array = 0
then '(select JSON_query(' + node_query + ',''$[0]'')) ' + node_name
else node_query + + node_name end
/* starting with highest nesting level substitute child subqueries ino
subquery hold in their parents
*/
declare @counter int = (select max(node_level) from #doc_schema)
while(@counter >= 0)
begin
update #doc_schema set node_query = replace(node_query,'###subqueries###', subs.subqueries)
from
(select parent_path, string_agg(node_query,',') subqueries, node_level from #doc_schema
group by parent_path, node_level ) subs
where subs.node_level = @counter and
#doc_schema.node_path = subs.parent_path
set @counter -= 1
end
/* objects and arrays with no subobjects or subarrays still have subquery holder so remove them
*/
update #doc_schema set node_query = replace(node_query,', ###subqueries###', '') where node_level = 0
declare @query nvarchar(max) = (select node_query from #doc_schema where node_level = 0)
/* add wrapper to query to specify column nave otherwise create view will fail
*/
set @query =
case when OBJECT_ID(@view_name + '_JSON', 'V') is NULL then 'create' else 'alter' end +
' view ' + @view_name + '_json as select' + @query + ' json'
exec sp_executesql @query