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--- |
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title: Query JSON with JMESPath |
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description: n8n supports the JMESPath library, to simplify working with JSON formatted data. |
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contentType: howto |
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--- |
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# Query JSON with JMESPath |
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[JMESPath](https://jmespath.org/){:target=_blank .external-link} is a query language for JSON that you can use to extract and transform elements from a JSON document. For full details of how to use JMESPath, refer to the [JMESPath documentation](https://jmespath.org/tutorial.html){:target=_blank .external-link}. |
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## The `jmespath()` method |
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n8n provides a custom method, `jmespath()`. Use this method to perform a search on a JSON object using the JMESPath query language. |
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The basic syntax is: |
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=== "JavaScript" |
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```js |
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$jmespath(object, searchString) |
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``` |
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=== "Python" |
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```python |
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_jmespath(object, searchString) |
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``` |
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To help understand what the method does, here is the equivalent longer JavaScript: |
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```js |
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var jmespath = require('jmespath'); |
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jmespath.search(object, searchString); |
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``` |
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/// note | Expressions must be single-line |
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The longer code example doesn't work in Expressions, as they must be single-line. |
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/// |
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`object` is a JSON object, such as the output of a previous node. `searchString` is an expression written in the JMESPath query language. The [JMESPath Specification](https://jmespath.org/specification.html#jmespath-specification){:target=_blank .external-link} provides a list of supported expressions, while their [Tutorial](https://jmespath.org/tutorial.html) and [Examples](https://jmespath.org/examples.html){:target=_blank .external-link} provide interactive examples. |
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/// warning | Search parameter order |
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The examples in the [JMESPath Specification](https://jmespath.org/specification.html#jmespath-specification){:target=_blank .external-link} follow the pattern `search(searchString, object)`. The [JMESPath JavaScript library](https://github.com/jmespath/jmespath.js/){:target=_blank .external-link}, which n8n uses, supports `search(object, searchString)` instead. This means that when using examples from the JMESPath documentation, you may need to change the order of the search function parameters. |
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/// |
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## Common tasks |
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This section provides examples for some common operations. More examples, and detailed guidance, are available in [JMESPath's own documentation](https://jmespath.org/tutorial.html){:target=_blank .external-link}. |
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When trying out these examples, you need to set the Code node **Mode** to **Run Once for Each Item**. |
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### Apply a JMESPath expression to a collection of elements with projections |
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From the [JMESPath projections documentation](https://jmespath.org/tutorial.html#projections){:target=_blank .external-link}: |
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> Projections are one of the key features of JMESPath. Use it to apply an expression to a collection of elements. JMESPath supports five kinds of projections: |
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> |
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> * List Projections |
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> * Slice Projections |
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> * Object Projections |
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> * Flatten Projections |
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> * Filter Projections |
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The following example shows basic usage of list, slice, and object projections. Refer to the [JMESPath projections documentation](https://jmespath.org/tutorial.html#projections){:target=_blank .external-link} for detailed explanations of each projection type, and more examples. |
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Given this JSON from a webhook node: |
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```js |
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[ |
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{ |
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"headers": { |
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"host": "n8n.instance.address", |
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... |
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}, |
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"params": {}, |
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"query": {}, |
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"body": { |
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"people": [ |
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{ |
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"first": "James", |
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"last": "Green" |
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}, |
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{ |
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"first": "Jacob", |
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"last": "Jones" |
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}, |
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{ |
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"first": "Jayden", |
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"last": "Smith" |
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} |
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], |
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"dogs": { |
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"Fido": { |
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"color": "brown", |
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"age": 7 |
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}, |
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"Spot": { |
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"color": "black and white", |
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"age": 5 |
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} |
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} |
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} |
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} |
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] |
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``` |
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Retrieve a [list](https://jmespath.org/tutorial.html#list-and-slice-projections){:target=_blank .external-link} of all the people's first names: |
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=== "Expressions (JavaScript)" |
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```js |
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{{$jmespath($json.body.people, "[*].first" )}} |
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// Returns ["James", "Jacob", "Jayden"] |
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``` |
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=== "Code node (JavaScript)" |
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```js |
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let firstNames = $jmespath($json.body.people, "[*].first" ) |
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return {firstNames}; |
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/* Returns: |
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[ |
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{ |
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"firstNames": [ |
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"James", |
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"Jacob", |
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"Jayden" |
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] |
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} |
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] |
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*/ |
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``` |
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=== "Code node (Python)" |
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```python |
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firstNames = _jmespath(_json.body.people, "[*].first" ) |
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return {"firstNames":firstNames} |
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""" |
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Returns: |
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[ |
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{ |
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"firstNames": [ |
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"James", |
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"Jacob", |
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"Jayden" |
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] |
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} |
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] |
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""" |
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``` |
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Get a [slice](https://jmespath.org/tutorial.html#list-and-slice-projections){:target=_blank .external-link} of the first names: |
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=== "Expressions (JavaScript)" |
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```js |
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{{$jmespath($json.body.people, "[:2].first")}} |
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// Returns ["James", "Jacob"] |
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``` |
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=== "Code node (JavaScript)" |
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```js |
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let firstTwoNames = $jmespath($json.body.people, "[:2].first"); |
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return {firstTwoNames}; |
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/* Returns: |
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[ |
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{ |
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"firstNames": [ |
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"James", |
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"Jacob", |
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"Jayden" |
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] |
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} |
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] |
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*/ |
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``` |
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=== "Code node (Python)" |
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```python |
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firstTwoNames = _jmespath(_json.body.people, "[:2].first" ) |
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return {"firstTwoNames":firstTwoNames} |
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""" |
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Returns: |
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[ |
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{ |
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"firstTwoNames": [ |
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"James", |
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"Jacob" |
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] |
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} |
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] |
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""" |
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``` |
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Get a list of the dogs' ages using [object projections](https://jmespath.org/tutorial.html#object-projections){:target=_blank .external-link}: |
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=== "Expressions (JavaScript)" |
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```js |
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{{$jmespath($json.body.dogs, "*.age")}} |
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// Returns [7,5] |
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``` |
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=== "Code node (JavaScript)" |
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```js |
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let dogsAges = $jmespath($json.body.dogs, "*.age"); |
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return {dogsAges}; |
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/* Returns: |
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[ |
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{ |
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"dogsAges": [ |
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7, |
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5 |
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] |
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} |
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] |
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*/ |
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``` |
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=== "Code node (Python)" |
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```python |
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dogsAges = _jmespath(_json.body.dogs, "*.age") |
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return {"dogsAges": dogsAges} |
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""" |
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Returns: |
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[ |
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{ |
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"dogsAges": [ |
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7, |
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5 |
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] |
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} |
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] |
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""" |
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``` |
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### Select multiple elements and create a new list or object |
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Use [Multiselect](https://jmespath.org/tutorial.html#multiselect){:target=_blank .external-link} to select elements from a JSON object and combine them into a new list or object. |
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Given this JSON from a webhook node: |
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```js |
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[ |
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{ |
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"headers": { |
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"host": "n8n.instance.address", |
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... |
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}, |
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"params": {}, |
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"query": {}, |
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"body": { |
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"people": [ |
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{ |
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"first": "James", |
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"last": "Green" |
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}, |
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{ |
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"first": "Jacob", |
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"last": "Jones" |
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}, |
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{ |
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"first": "Jayden", |
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"last": "Smith" |
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} |
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], |
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"dogs": { |
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"Fido": { |
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"color": "brown", |
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"age": 7 |
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}, |
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"Spot": { |
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"color": "black and white", |
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"age": 5 |
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} |
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} |
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} |
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} |
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] |
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``` |
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<!-- vale off --> |
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Use multiselect list to get the first and last names and create new lists containing both names: |
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<!-- vale on --> |
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=== "Expressions (JavaScript)" |
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[[% raw %]] |
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```js |
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{{$jmespath($json.body.people, "[].[first, last]")}} |
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// Returns [["James","Green"],["Jacob","Jones"],["Jayden","Smith"]] |
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``` |
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[[% endraw %]] |
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=== "Code node (JavaScript)" |
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```js |
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let newList = $jmespath($json.body.people, "[].[first, last]"); |
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return {newList}; |
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/* Returns: |
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[ |
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{ |
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"newList": [ |
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[ |
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"James", |
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"Green" |
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], |
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[ |
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"Jacob", |
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"Jones" |
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], |
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[ |
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"Jayden", |
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"Smith" |
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] |
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] |
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} |
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] |
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*/ |
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``` |
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=== "Code node (Python)" |
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```python |
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newList = _jmespath(_json.body.people, "[].[first, last]") |
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return {"newList":newList} |
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""" |
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Returns: |
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[ |
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{ |
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"newList": [ |
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[ |
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"James", |
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"Green" |
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], |
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[ |
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"Jacob", |
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"Jones" |
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], |
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[ |
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"Jayden", |
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"Smith" |
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] |
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] |
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} |
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] |
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""" |
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``` |
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### An alternative to arrow functions in expressions |
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For example, generate some input data by returning the below code from the Code node: |
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```js |
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return[ |
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{ |
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"json": { |
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"num_categories": "0", |
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"num_products": "45", |
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"category_id": 5529735, |
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"parent_id": 1407340, |
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"pos_enabled": 1, |
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"pos_favorite": 0, |
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"name": "HP", |
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"description": "", |
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"image": "" |
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} |
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}, |
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{ |
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"json": { |
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"num_categories": "0", |
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"num_products": "86", |
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"category_id": 5529740, |
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"parent_id": 1407340, |
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"pos_enabled": 1, |
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"pos_favorite": 0, |
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"name": "Lenovo", |
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"description": "", |
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"image": "" |
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} |
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} |
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] |
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``` |
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You could do a search like "find the item with the name Lenovo and tell me their category ID." |
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```js |
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{{ $jmespath($("Code").all(), "[?json.name=='Lenovo'].json.category_id") }} |
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``` |
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