Add new element to existing JSON array with jq

I want to append an element to an array in a JSON file using the jq``add command, but it's not working.

report-2017-01-07.json file:

{  
   "report": "1.0",
   "data": {  
      "date": "2010-01-07",
      "messages": [  
         {  
            "date": "2010-01-07T19:58:42.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "OK",
            "message": "metadata loaded into iRODS successfully"
         },
         {  
            "date": "2010-01-07T20:22:46.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "NOK",
            "message": "metadata duplicated into iRODS"
         },
         {  
            "date": "2010-01-07T22:11:55.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "NOK",
            "message": "metadata was not validated by XSD schema"
         }
      ]
   }
}

I am using this command:

$ cat report-2017-01-07.json 
| jq -s '.data.messages {"date": "2010-01-07T19:55:99.999Z", "xml": "xml_samplesheet_2017_01_07_run_09.xml", "status": "OKKK", "message": "metadata loaded into iRODS successfullyyyyy"}'
jq: error: syntax error, unexpected '{', expecting $end (Unix shell quoting issues?) at <top-level>, line 1:
.data.messages {"date": "2010-01-07T19:55:99.999Z", "xml": "xml_samplesheet_2017_01_07_run_09.xml", "status": "OKKK", "message": "metadata loaded into iRODS successfullyyyyy"}               
jq: 1 compile error

Here's how I want the output to look:

{
    "report": "1.0",
    "data": {
        "date": "2010-01-07",
        "messages": [{
            "date": "2010-01-07T19:58:42.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "OK",
            "message": "metadata loaded into iRODS successfully"
        }, {
            "date": "2010-01-07T20:22:46.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "NOK",
            "message": "metadata duplicated into iRODS"
        }, {
            "date": "2010-01-07T22:11:55.949Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "NOK",
            "message": "metadata was not validated by XSD schema"
        }, {
            "date": "2010-01-07T19:55:99.999Z",
            "xml": "xml_samplesheet_2017_01_07_run_09.xml",
            "status": "OKKKKKKK",
            "message": "metadata loaded into iRODS successfullyyyyy"
        }]
    }
}

Solution

The |= .+ part in the filter adds a new element to the existing array. You can use jq with filter like:

jq '.data.messages[3] |= . + {
      "date": "2010-01-07T19:55:99.999Z", 
      "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
      "status": "OKKK", 
      "message": "metadata loaded into iRODS successfullyyyyy"
}' inputJson

To avoid using the hardcoded length value 3 and dynamically add a new element, use . | length which returns the length, which can be used as the next array index, i.e.,

jq '.data.messages[.data.messages| length] |= . + {
      "date": "2010-01-07T19:55:99.999Z", 
      "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
      "status": "OKKK", 
      "message": "metadata loaded into iRODS successfullyyyyy"
}' inputJson

(or) as per peak's suggestion in the comments, using the += operator alone

jq '.data.messages += [{
     "date": "2010-01-07T19:55:99.999Z",
     "xml": "xml_samplesheet_2017_01_07_run_09.xml", 
     "status": "OKKK", 
     "message": "metadata loaded into iRODS successfullyyyyy"
}]'

which produces the output you need:

{
  "report": "1.0",
  "data": {
    "date": "2010-01-07",
    "messages": [
      {
        "date": "2010-01-07T19:58:42.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "OK",
        "message": "metadata loaded into iRODS successfully"
      },
      {
        "date": "2010-01-07T20:22:46.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "NOK",
        "message": "metadata duplicated into iRODS"
      },
      {
        "date": "2010-01-07T22:11:55.949Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "NOK",
        "message": "metadata was not validated by XSD schema"
      },
      {
        "date": "2010-01-07T19:55:99.999Z",
        "xml": "xml_samplesheet_2017_01_07_run_09.xml",
        "status": "OKKK",
        "message": "metadata loaded into iRODS successfullyyyyy"
      }
    ]
  }
}

Use jq-play to dry-run your jq-filter and optimize any way you want.