When you run a request, Data Fetcher converts the API response into a table of fields and records that can be written to your destination Airtable table. You can control how this data is structured using response field mapping and data transformation settings.
Data Fetcher offers two ways to handle nested arrays in your API responses: Single record per item and Expand nested items. The key difference is whether nested arrays stay combined in one record or are expanded into multiple records.
Let’s use this sample JSON response to illustrate both approaches:
[
{
"id": "company1",
"positions": [{ "id": "position1" }, { "id": "position2" }]
},
{
"id": "company2",
"positions": [{ "id": "position3" }, { "id": "position4" }]
}
]
Single record per item
Single record per item keeps each parent entity in one row by combining nested values with commas. Each company stays in its own record:
| Id | Positions id |
|---|
| company1 | position1,position2 |
| company2 | position3,position4 |
Single record per item doesn’t mean the entire response becomes one record.Data Fetcher finds the first array in the response and creates one record for each item in that array.
Expand nested items
Expand nested items creates a new record for each item in a nested array. Parent fields are duplicated so each nested item has its own row.
| Id | Positions id |
|---|
| company1 | position1 |
| company1 | position2 |
| company2 | position3 |
| company2 | position4 |
- On the create screen, open Advanced settings.
- Under Data Transformation, select either Single record per item or Expand nested items.
Advanced Single record per item options
Combine nested object keys
By default, nested object values are combined into a comma-separated field. Using our example above, all positions.id values become a single-line text field called Positions id.
You can disable this to create separate numbered fields instead:
| Id | Positions 1 id | Positions 2 id |
|---|
| company1 | position1 | position2 |
| company2 | position3 | position4 |
- In advanced settings, ensure transformation is set to Single record per item.
- Turn off Combine nested object keys.
Combine arrays of text/numbers
Similarly, arrays of text or numbers are combined into a comma-separated value by default. For this response:
[
{
"id": "company1",
"categories": ["Fintech", "Startup"]
},
{
"id": "company2",
"categories": ["Healthtech", "Public", "Unicorn"]
}
]
| Id | Categories |
|---|
| company1 | Fintech,Startup |
| company2 | Healthtech,Public,Unicorn |
- In advanced settings, ensure transformation is set to Single record per item.
- Turn off Combine arrays of text/numbers.
Custom separators
Instead of commas, you can specify a custom separator for combined values. This is useful if your data already contains commas and you need a different delimiter such as the pipe symbol (|).
Both Combine nested object keys and Combine arrays of text/numbers use the separator you specify in the Separator input field.
Need More Control?
For more advanced control over how your response is structured, you can use a response JMESPath to customize exactly how the data is extracted and transformed. 
