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Using regular expressions in payloads

In some operations (both in NGSIv1 and NGSIv2) regular expressions can be used, as shown below. The set of supported regular expressions is POSIX Extended (see details here).

NGSIv1 example:

POST /v1/queryContext

{
  "entities": [
    {
      "type": "Sensor",
      "isPattern": "true",
      "id": ".*"
    }
  ]
}

NGSIv2 example:

POST /v2/op/query

{
  "entities": [
    {
      "idPattern": ".*",
      "type": "Sensor"
    }
  ]
}

The regular expression language allows the usage of backslash (\). For example, SENSOR\d{2} matches strings containing SENSOR followed by two digits. However, note that \ is a special character in JSON, which, according to the JSON specification, needs to be encoded as \\.

POST /v1/queryContext

{
  "entities": [
    {
      "type": "Sensor",
      "isPattern": "true",
      "id": "SENSOR\\d{2}"
    }
  ]
}

NGSIv2 example:

POST /v2/op/query

{
  "entities": [
    {
      "idPattern": "SENSOR\\d{2}",
      "type": "Sensor"
    }
  ]
}

The issue could be even funnier if you use the shell to send the request. For example, if you use multi-line curl you need to escape \ at shell level. Eg:

curl localhost:1026/v2/op/query -s -S --header 'Content-Type: application/json' --header 'Accept: application/json' -d @- | python -mjson.tool) <<EOF
{
  "entities": [
    {
      "idPattern": "SENSOR\\\\d{2}",
      "type": "Sensor"
    }
  ]
}
EOF

In other words, the SENSOR\\\\d{2} string at shell level is transformed to SENSOR\\d{2} at payload level (i.e. the actual HTTP request that is sent over the wire) which, in sequence, corresponds to the SENSOR\d{2} regular expression after JSON parsing stage at Orion. However, note that if you use a file for your payload, the shell escaping isn't needed, i.e.:

curl localhost:1026/v2/op/query -s -S --header 'Content-Type: application/json' --header 'Accept: application/json' -d @payload.json

would use the following payload.json file:

{
  "entities": [
    {
      "idPattern": "SENSOR\\d{2}",
      "type": "Sensor"
    }
  ]
}

More details on this can be found in the following issue comment at github.