Créer des tableaux JSON imbriqués à l'aide de FOR JSON PATH
J'ai besoin de créer une sortie JSON à partir d'une requête qui utilise la jointure interne entre deux tables avec une relation un à plusieurs.
Je voudrais que les valeurs de la table secondaire soient imbriquées en tant que propriétés de tableau de la table primaire.
Prenons l'exemple suivant:
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')
Et interrogez:
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
Cela imprimera le JSON suivant:
{
"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"}}}
]
}
Cependant, j'aimerais avoir les données des animaux de compagnie sous forme de tableaux dans les données des propriétaires:
{
"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"}
}
}
]
}
Comment puis-je faire ceci?
Vous pouvez utiliser la requête suivante:
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')
Pour plus d'informations, voir https://blogs.msdn.Microsoft.com/sqlserverstorageengine/2015/10/09/returning-child-rows-formatted-as-json-in-sql-server-queries/
Avec les tableaux profondément imbriqués, les sous-requêtes deviennent rapidement ingérables:
select id,foo, (select id, bar, (select ... for json path) things,
(select...) more_things) yet_more, select(...) blarg
Je crée une vue relationnelle (non json) qui joint toutes mes tables et a la structure json intégrée dans les alias de colonne, tout comme pour le chemin json le fait. Mais j'ai aussi [] pour indiquer que le nœud json est un tableau. Comme ça:
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 .....
J'ai écrit une procédure stockée qui crée une vue json dans la vue non-json qui analyse les noms de colonne de la vue relationnelle et rend le json joli. Voir ci-dessous. Appelez-le avec le nom de votre vue relationnelle et cela crée une vue. Ce n'est pas complètement testé mais ça marche pour moi. La seule mise en garde est que les tables doivent avoir id colonnes appelées id. Il utilise string_agg () et json_array () à la version de sql doit être assez nouveau. Il est également configuré pour renvoyer un tableau à la racine. Il faudra peaufiner pour renvoyer un objet.
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