Create nested JSON arrays using FOR JSON PATH
You can use the following query:
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')For more information, see https://blogs.msdn.microsoft.com/sqlserverstorageengine/2015/10/09/returning-child-rows-formatted-as-json-in-sql-server-queries/
With deeply nested arrays the subqueries get unmanageable quickly:
select id,foo, (select id, bar, (select ... for json path) things, (select...) more_things) yet_more, select(...) blargI create a relational (non-json) view that joins all my tables and has the json structure embedded in the column aliases, just like for json path does. But I also have [] to indicate that the json node is an array. Like this:
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 pjoin children c on c.parent_id = p.id .....I wrote a stored procedure that creates a json view into the non-json view that parses the column names of the relational view and makes the json pretty. See below. Call it with the name of your relational view and it creates a view. It's not thoroughly tested but it works for me. Only caveat is that tables need to have id columns called id. It uses string_agg() and json_array() to the version of sql needs to be pretty new. It's also set up to return an array in the root. It will need tweaking to return an object.
create procedure create_json_from_view@view_name varchar(max)ascreate 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) > 0AND RIGHT(COLUMN_NAME,LEN(VALUE)) <> VALUEand table_name = @view_name/* node_name past rightmost period or the same as node_path if there is no periodalso 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_columnsfrom ( 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) sub2where #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 -= 1end/* 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 = 0declare @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
I have made below json format by following @Razvan Socol.
JSON
[ "domain_nm": "transactions", "tables": [ { "tableName": "transactions_details", cols: [ { "col_nm": "audit_transactions_details_guid", "col_data_typ": "string" } ] } ] ]SQL
select outer1.DOMAIN_NM as domain_nm, (select inner2.TBL_NM as tableName, (select inner1.COL_NM as col_nm, inner1.COL_DATA_TYP as col_data_typ from ONBD_MTDT.CDM_TBL inner1 where inner1.TBL_NM=inner2.TBL_NM FOR JSON PATH ) as cols from ONBD_MTDT.CDM_TBL inner2 where inner2.DOMAIN_NM=outer1.DOMAIN_NM group by inner2.DOMAIN_NM,inner2.TBL_NM FOR JSON PATH ) as tablesfrom ONBD_MTDT.CDM_TBL outer1 group by outer1.DOMAIN_NMFOR JSON PATH