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107 lines
3.1 KiB
Markdown
107 lines
3.1 KiB
Markdown
---
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contentType: explanation
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---
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# How n8n structures data
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Understanding how n8n structures and passes data between nodes is fundamental to building workflows. This guide covers both the data structure format and how data flows through your workflow.
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## Data structure
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In n8n, all data passed between nodes is an array of objects. It has the following structure:
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```json
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[
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{
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// For most data:
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// Wrap each item in another object, with the key 'json'
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"json": {
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// Example data
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"apple": "beets",
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"carrot": {
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"dill": 1
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}
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},
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// For binary data:
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// Wrap each item in another object, with the key 'binary'
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"binary": {
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// Example data
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"apple-picture": {
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"data": "....", // Base64 encoded binary data (required)
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"mimeType": "image/png", // Best practice to set if possible (optional)
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"fileExtension": "png", // Best practice to set if possible (optional)
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"fileName": "example.png", // Best practice to set if possible (optional)
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}
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}
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},
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]
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```
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/// note | Skipping the `json` key and array syntax
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From 0.166.0 on, when using the Function node or Code node, n8n automatically adds the `json` key if it's missing. It also automatically wraps your items in an array (`[]`) if needed. This is only the case when using the Function or Code nodes. When building your own nodes, you must still make sure the node returns data with the `json` key.
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///
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## How data flows within nodes
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When you connect nodes in a workflow, data automatically passes from one node to the next.
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Nodes process multiple items automatically. When a node receives an array of data items, it processes each item individually and performs the configured operation for each one.
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For example, if you set the Trello node to `Create-Card`, and create an expression that sets `Name` using a property called `name-input-value` from the incoming data, the node creates a card for each item, always choosing the `name-input-value` of the current item.
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For example, this input will create two cards. One named `test1` the other one named `test2`:
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```json
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[
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{
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"name-input-value": "test1"
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},
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{
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"name-input-value": "test2"
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}
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]
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```
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## Understand what you're mapping with drag and drop
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Data mapping maps the field path, and loads the field's value. For example, given the following data:
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```js
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[
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{
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"fruit": "apples",
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"color": "green"
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}
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]
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```
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You can map `fruit` by dragging and dropping **fruit** from the **INPUT** into the field where you want to use its value. This creates an expression, `{{ $json.fruit }}`. When the node iterates over input items, the value of the field becomes the value of `fruit` for each item.
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## Understand nested data
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Given the following data:
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```js
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[
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{
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"name": "First item",
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"nested": {
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"example-number-field": 1,
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"example-string-field": "apples"
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}
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},
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{
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"name": "Second item",
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"nested": {
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"example-number-field": 2,
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"example-string-field": "oranges"
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}
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}
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]
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```
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n8n displays it in table form like this:
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