【问题】
A valid form of a JSON document begins as an Array element. How do you access any element using the JsonDataSource “jsonpath” to query it? I have tried using the standard $[0] for the top level fields and as “$” for creating my subdataset but neither works… when I place the array under a standard element it works fin,e but that is not the format of our JSON.

My JSON loks a bit like this:

[  {      “race”: {          “raceId”: “1.33.1141109.2”,          “startDate”: “2014-11-09T13:15:00.000Z”,          “raceClassification”: {             “classification”: “Novices’”         },          “raceType”: {            “key”: “H”         },          “raceClass”: 4,          “course”:          {            “courseId”: “1.33”         },          “meetingId”: “1.33.1141109”       },       “numberOfRunners”: 2,       “runners”: [         {             “horseId”: “1.00387464”,             “trainer”: {                “trainerId”: “1.00034060”            },             “ownerColours”: “Maroon, pink sleeves, dark blue cap.”          },          {            “horseId”: “1.00373620”,             “trainer”: {                “trainerId”: “1.00010997”            },             “ownerColours”: “Black, emerald green cross of lorraine, striped sleeves.”          }       ]    },    {      “race”: {          “raceId”: “1.33.1141109.3”,          “startDate”: “2014-11-09T13:45:00.000Z”,          “raceClassification”:  {             “classification”: “Handicap”         },          “raceType”: {            “key”: “C”         },          “raceClass”: 4,          “course”: {            “courseId”: “1.33”         },          “meetingId”: “1.33.1141109”       },       “numberOfRunners”: 2,       “runners”: [         {             “horseId”: “1.00297339”,             “trainer”:             {                “trainerId”: “1.00000577”            },             “ownerColours”: “Maroon and light blue (quartered), maroon sleeves.”          },          {            “horseId”: “1.00333030”,             “trainer”:             {                “trainerId”: “1.00000065”,            },             “ownerColours”: “Emerald green, yellow hoops, white cap.”          }       ]    } ]

输入参数（比如 1 或 2），从 json 文件中取出数组中指定成员的三个字段：horseId, trainerId,ownerColours。比如输入 1，结果应该是：

1.003874641.00034060Maroon, pink sleeves, dark blue cap.

1.003736201.00010997Black, emerald green cross of lorraine, striped sleeves.

【回答】

使用 SPL 处理 json 数据后可以快速获取所需要的信息，代码如下：

运行结果：​

A1：读取 json 串

A2：解析 json 形成序表

A3：指定数组成员，which 是参数名本例中可以取 1 或者 2，获得节点二维表

A4：提取所需要的三个字段，生成新序表，其中 trainerId 要从下级取。