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Punch

The punch node lets you run a punchlet on incoming Dataset rows. Say you receive a dataset as follows:

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|  column1 | column2 | column3 |
|  "hello" | true    | 17      |
 ...

The punchlet will receive a json document like this:

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  {
    "column1" : "hello",
    "column2" : true,
    "column3" : 17
  }

The punchlet can produce one or several additional columns. Here is a punchlet that will simply add two additional columns: 

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{
  [column4] = [column1] + " world";
  [column5] = [column3] * 2;
}

This will produce the following rows

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|  column1 | column2 | column3 | column4        | column5 |
|  "hello" | true    | 17      | "hello world"  | 34      |
 ...

To achieve this here is the node definition:

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  {
    type: punch_batch
    component: punch
    settings:
    {
      punchlet_code: 
      '''
      {
        [column4] = [column1] + "world";
        [column5] = [column3] * 2;
      }
      '''
      output_columns: [
        {
          type: string
          field: column4
        }
        {
          type: integer
          field: column5
        }
      ]
    }
    subscribe:
    [
      {
        component: input
        stream: documents
      }
    ]
    publish:
    [
      {
        stream: documents
      }
    ]
  }

Selecting Input Columns

You can select only some of the input columns using the input_columns property as follows

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  {
    type: punch_batch
    component: punch
    settings:
    {
      punchlet_code:
      '''
      {
        [column4] = [column1] + "world";
        [column5] = [column3] * 2;
      }
      '''
      input_columns: [ column1 , column3 ]
      ...
    }

Generating Several Rows

Your punchlet can output an array of values instead of just a single json document. In that case, as many rows will be generated in the output dataset. 

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      punchlet_code:
      '''
      {
        Tuple results;
        for (int i = 0; i < 3; i++) {
          Tuple tmp;
          tmp:[column4] = [column1] + i;
          tmp:[column5] = [column3] + i;
          results.append(tmp);
        }
        // this is a notation to overwrite the top level document
        root:/ = results;
      }
      '''

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|  column1 | column2 | column3 | column4    | column5 |
|  "hello" | true    | 17      | "hello 0"  | 17      |
|  "hello" | true    | 17      | "hello 1"  | 18      |
|  "hello" | true    | 17      | "hello 2"  | 19      |

Resources

Output documents will be appended in the output dataset. For each input document, the punch can either provide an output document, or multiple output documents (by providing an array as root tuple).

You can also provide external resources by adding it in resources setting or by named subscription tagged with resource. Those resources are accessible in punchlet code through the Java function:

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/**
 * Return a provided resource
 * @param resourceName name of the resource (subscription name or "resources" map key)
 * @param resourceTtype type of the resource
 * @return the resource
 */
public <T> T getResource(String resourceName, Class<T> resourceTtype)

Warning

You must use this node instead of punch_stage if you need to provide a resource from an other node during punchlet execution.

Settings

  • punchlet_code: String : "{}"

    Punchlet code. Override "punchlet_code_file".

  • punchlet_code_file: String

    Punchlet code file readable from driver

  • input_columns: [String]

    If not set, all the dataset row columns will be visible to the punchlet. You can specifically narrow the number of exposed columns by defining input_columns.

  • output_column: [Json]

    List of additional columns, i.e. the one added by the punchlet

  • resources: Json

    Map of resources provided during punchlet execution

Info

you can use the ''' special hjson tag to include punchlet code in a more readable and unecaped way. An example follows.