USQL Query to create a Table from Json Data

Question

I have a json which is like [{}, {}, {}], i.e. there can be multiple rows and each row has a number of property - value pairs, which remain fixed for each row.<

Answer 1

Found a solution below that worked in my small test case - I agree that the {"Name: 'XXX', Value: 'YYY'} formatting makes things a little tricky but you can still get this done without a custom extractor - just lots of nested JSON.

Basically, you extract a SQLArray from the System and Details JSON (in @parse_json), then split those into smaller JSON tuples (in @get_nested), and then finally extract the "Values" in @output. See code below. Let me know if you have questions!

    CREATE ASSEMBLY [Microsoft.Analytics.Samples.Formats]
    FROM @FormatsAssembly;

    CREATE ASSEMBLY [Newtonsoft.Json]
    FROM @JSONAssembly;

    REFERENCE ASSEMBLY [Newtonsoft.Json];
    REFERENCE ASSEMBLY [Microsoft.Analytics.Samples.Formats];

    DECLARE @CommentsPath = "/JSONTest/rawJson.json";


    @get_json =
        EXTRACT 
            MainId          int,
            System          string,
            Details         string,
            ttl             int
        FROM @CommentsPath
        USING new Microsoft.Analytics.Samples.Formats.Json.JsonExtractor();


    @parse_json =
        SELECT MainId, 
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(System).Values AS SystemJson,
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(Details).Values AS DetailsJson,
               ttl
        FROM @get_json;


    @get_nested =
        SELECT 
               MainId,
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(SystemJson[0]) AS SystemName,
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(SystemJson[1]) AS SystemId,
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(DetailsJson[0]) AS DetailsName,
               Microsoft.Analytics.Samples.Formats.Json.JsonFunctions.JsonTuple(DetailsJson[1]) AS DetailsPrevid,
               ttl
        FROM @parse_json;

    @output =
        SELECT MainId,
               SystemName["Value"] AS SystemEvent,
               SystemId["Value"] AS SystemId,
               DetailsName["Value"] AS EventName,
               DetailsPrevid["Value"] AS PrevId,
               ttl
        FROM @get_nested;

    OUTPUT @output 
        TO @"/JSONTest/test1.csv"
        USING Outputters.Csv(outputHeader : true);