Using key/value pairs

Update a structure to be able to map key/value pairs.

Before you begin

You have created an input and an output structure. You can use the JSON samples below to create your structures.

About this task

In this example, you have a JSON file with an items object that contains information about bicycles and scooters. Each item is an object with the item name as the key, and the value is an object containing the description and the price of the item. The goal is to create an output with an array of items.

The input data looks like this:

{
    "items": {
        "MBIKE": {
            "description": "27.5 inch electric mountain bike",
            "price": "899.99"
        },
        "EBIKE": {
            "description": "Electric hybrid bike",
            "price": "999.99"
        },
        "WBIKE": {
            "description": "Women's road bike",
            "price": "299.99"
        },
        "ESCOOT": {
            "description": "Camou electric scooter",
            "price": "749.0"
        },
        "EVSCOOT": {
            "description": "Folding electric velocity+ scooter",
            "price": "599.99"
        },
        "KSCOOT": {
            "description": "24 volt kid scooter",
            "price": "299.99"
        }
    }
}

The output structure looks like this:

{
    "items": [
        {
            "make": "",
            "description": "",
            "price": ""
        }
    ]
}

Procedure

Open the input structure you created and expand the items element.
The items element contains one child for each type of item present in the JSON file. This means the structure would not be usable if more items were added, so you need to update the structure to make it generic.
Click Read Only and select Editable in the drop-down list.
Click items and select Map in the Group Type drop-down list.
A dialog box appears to indicate that changing the element type to Map will replace the element's children. If you click Yes, an entry loop containing a key element and a value element will be created automatically.
Right-click value and create two new elements named description and price, then save the structure.
The final structure looks like this:

You can close and reopen the structure to check the highlighting in the Document tab.
Create a new DSQL Map and add the input and output structures.
Map the following elements using drag-and-drop:
- key to make
- description to description
- price to price
Click items and add the following line under the existing expression to filter the output data:
```
WHERE value.price <= items['ESCOOT'].price
```
This expression indicates that the map should only return items with a price lower than or equal to the price of the ESCOOT input element. You can see that the value is referenced using a specific key. For more information, see the Talend Data Shaping Language Reference Guide.

Results

Your map is configured, you can use the Test Run feature to check the result. In this example, the following result is returned:

{
   "items":[
      {
         "make":"ESCOOT",
         "description":"Camou electric scooter",
         "price":"749.0"
      },
      {
         "make":"WBIKE",
         "description":"Women's road bike",
         "price":"299.99"
      },
      {
         "make":"KSCOOT",
         "description":"24 volt kid scooter",
         "price":"299.99"
      },
      {
         "make":"EVSCOOT",
         "description":"Folding electric velocity+ scooter",
         "price":"599.99"
      }
   ]
}

You can also do the opposite and use a map to create an output with key/value pairs, for example:

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