Description

Json output step allows to generate json blocks based on input step values. Output json will be available as java script array or java script object depends on step settings.

Transformation with json output usage example

Options

General Tab

General tab allows to specify type of step operation, output json structure, step output file. This file will be used to dump all generated json.

Settings

See detailed settings description below.

Compatibility mode was introduced since PDI 4.3.0 version. This was designed to handle fix with changes to json structure generation. By default new fixed mode is used. To enable compatibility mode check 'Compatibility mode' check box.

For example step has a row input data with 2 fields: field "name" with string value "item" and field "value" with numeric value 25. We have 4 rows of data with "name" and "value". 

Consider Json output step has settings combination:

• 'Json block name' = "data"
• 'Nr rows in block' = 3
• 'Compatibility mode' NOT checked (and this is the default option)

step will generate output:

{
  "data" : [ {
    "name" : "item",
    "value" : 25
  }, {
    "name" : "item",
    "value" : 25
  }, {
    "name" : "item",
    "value" : 25
  } ]
}{
  "data" : [ {
    "name" : "item",
    "value" : 25
  } ]
}

So We have 2 objects, first object has a 'data' (Json block name) array contains 3 json objects (because of number rows in a block is 3) and second object with array contains only one object. 3+1 is actually 4 rows processed.

If compatibility mode is enabled and step has settings combination like:

• Json block name = "data"
• Nr rows in block = 3
• 'Compatibility mode' is checked

step will generate output:

{"data":[{"name":"item"},{"value":25},{"name":"item"},{"value":25},{"name":"item"},{"value":25}]}
{"data":[{"name":"item"},{"value":25}]}

Pretty formatting does not affect compatibility mode. We have 2 output json objects. First object harvest first 3 input rows and second object harvests only one row. This happens because of number of rows in a block is 3. Anyway it can be considered as incorrect result, as the real object count for array is 6 for the first output object. By default compatibility mode is disabled.

If 'Json block name' is an empty string (by default it has 'data' value) - compatibility mode will use empty string for block name. Normally - if compatibility mode was not checked, step output will be:

[ {
  "name" : "item",
  "value" : 25
}, {
  "name" : "item",
  "value" : 25
}, {
  "name" : "item",
  "value" : 25
} ][ {
  "name" : "item",
  "value" : 25
} ]

So we have 2 json arrays, first array contains 3 items, second array contains one item.

Another special case is when 'Nr. rows in a block' = 1.
If used with empty json block name output will looks like:

{
  "name" : "item",
  "value" : 25
}{
  "name" : "item",
  "value" : 25
}{
  "name" : "item",
  "value" : 25
}{
  "name" : "item",
  "value" : 25
}

We will have just 4 simple json objects that will be outputted as a 4 step output rows.

In case of json block name is defined - output structure will looks like:

{
  "data" : {
    "name" : "item",
    "value" : 25
  }
}{
  "data" : {
    "name" : "item",
    "value" : 25
  }
}{
  "data" : {
    "name" : "item",
    "value" : 25
  }
}{
  "data" : {
    "name" : "item",
    "value" : 25
  }
}

So this is will be same 4 output objects with json block name defined.

If 'Nr. rows in a block' will be less that 1 output will be as a one object:

{
  "data" : [ {
    "name" : "item",
    "value" : 25
  }, {
    "name" : "item",
    "value" : 25
  }, {
    "name" : "item",
    "value" : 25
  }, {
    "name" : "item",
    "value" : 25
  } ]
}

This will be one object (one output row) with data block containing json array with 4 objects (as we had 4 input data rows). Please note - when using 0 'Nr. rows in a block' step will build output object until input data is available. When input is done - one big output object will be passed to output row. For big input data it can impact memory usage.

Output File

Fields Tab

This tab is used to map input step fields to output json values

Metadata Injection Support

All fields of this step support metadata injection. You can use this step with ETL Metadata Injection to pass metadata to your transformation at runtime.