Houdini 18.5 Nodes TOP nodes

JSON Input TOP node

Extracts data from JSON files and creates attributes

On this page
Since 17.5

This node will read in JSON files and extract data that is specified by the user. The user can specify the name of the work item attribute in which the data will be placed as well as its type and list index.

Tip

The $HH/help/files/pdg_examples/top_jsonpipeline example shows how you can use this node to create work items from a .json file.

TOP Attributes

json_arrayindex

integer

When performing the Array Retrieve operation, this will be set to the object’s index in the array from which it was retrieved, or to 0 if the retrieved value was not stored in an array.

obj_index

integer

When performing the Array Retrieve operation, this will be set to the index of the object. This is useful when performing queries that use the wildcard operator, as this attribute acts as an identifier of the object from which the information was retrieved.

query

string

When performing the Array Retrieve operation, this shows the query that was used to conduct the operation. If the wildcard operator was used in the query, the wildcard will be replaced with the resolved value.

field

string

When performing the Array Retrieve operation, this attribute is set to the field that was retrieved during the operation.

Parameters

Node

Generate When

Determines when this node will generate work items. You should generally leave this set to "Automatic" unless you know the node requires a specific generation mode, or that the work items need to be generated dynamically.

All Upstream Items are Generated

This node will generate work items once all of the input nodes have generated their work items.

All Upstream Items are Cooked

This node will generate work items once all of the input nodes have cooked their work items.

Each Upstream Item is Cooked

This node will generate work items each time a work item in an input node is cooked.

Automatic

The generation mode is selected based on the generation mode of the input nodes. If any of the input nodes are generating work items when their inputs cook, this node will be set to Each Upstream Item is Cooked. Otherwise, it will be set to All Upstream Items are Generated.

Source

JSON File

The source of the JSON file

Upstream Output File

Uses the output file produced by the upstream work item as the path to the JSON file.

Custom File Path

JSON file specified by a custom filepath.

File Tag

The data tag used to select the result from the upstream work item.

File Path

The path to the JSON file.

Operation

Operation

This specifies the retrieval operation that you want to perform.

Retrieve

This operation allows single data extractions to be performed on the JSON file. For example, it can be used to query a specific value in an object or a value at a certain index in a list. The Data Extractions multiparameter specifies the extractions that should be performed on the JSON.

Array Retrieve

This operation allows a specified field to be extracted from each index of a list within the JSON file.

Deserialize Work Item

This operation will deserialize a workitem from the given JSON file, the file should be formatted as a serialized work item file, such as that produced by JSON Output.

On Query Failure

This parameter controls what happens when any part of the query fails. An example of a query failure would be using an index in the query that is larger than the size of the array that is being indexed.

If the node is set to Raise Error mode, the node will automatically fail the entire operation when a query fails.

If the node is set to Add Warning mode, the node will attach a warning but the node will finish cooking. If an Array Retrieve operation is being performed, the node will attempt to complete the other queries.

Add Warning mode is useful if the JSON file contains non-uniform data – for example, when an array of objects may or may not contain a specific sub-object.

Data Extractions

The parameters in this multiparameter are used to specify the data extractions that should be performed when using the Retrieve operation.

Query

This parameter is used to specify the path to the JSON object or value that you want to extract. It uses a hierarchical syntax separated by "/" characters to specify the path. If an list is within the hierarchy, a number can be used to specify the array index.

If we have the following JSON file:

{ "plants" : [ { "name" : "tree", "inMyGarden" : true, "height" : 5.5 }, { "name" : "sunflower", "inMyGarden": false, "height" : 3 } ] }

And we wanted to retrieve the height of the first plant, the query would be:

plants/0/height

If we wanted to retrieve the name of the second plant, the query would be:

plants/1/name

When performing the Array Retrieve operation, the query must point to a list in the JSON, with one exception described below.

The Array Retrieve operation can make use of the wildcard (*) operator in its queries. The wildcard will cause branching traversal of the JSON hierarchy, where each object at that level becomes a branch of the JSON traversal.

If we have the following JSON file:

{ "Houdini" : { "Contexts" : { "Sop" : { "mountain" : { "name" : "Mountain" }, "polybevel" : { "name" : "PolyBevel" } }, "Top" : { "jsoninput" : { "name" : "Json Input" }, "jsonoutput" : { "name" : "Json Output" } } } } }

And we wanted to go the names of all the nodes in this JSON file, we could perform the following query:

Houdini/Contexts/*/*

with the field parameter set to name.

This will create 4 separate work items, each containing a node name. Note that json_arrayindex will be set to 0 on each, because these objects are all independent and not part of the same array.

Field

This parameter is only used when the Array Retrieve operation is being performed. It is used to specify the property that should be retrieved from each array index in the list pointed to by the query.

If the array pointed to by the Query is filled with anonymous objects (such as an array of integers), this parameter can be set to the wildcard operator (*) which simply means that it will get everything in the array.

Attribute Name

This specifies the name of the work item attribute to store the extracted value in.

Store As

This specifies what type of PDG attribute will be used to store the queried JSON data. If a specific PDG attribute type choice is selected and the JSON data type does not match, it will result in an error. JSON objects will be stored as PyObjects when the Automatic option is chosen.

Automatic

The type of the PDG attribute to use will be automatically determined from the type of the JSON data.

String

The data will be stored as a string attribute.

Integer

The data will be stored as an integer attribute.

Float

The data will be stored as a float attribute.

PyObject

The data will be stored as a PyObject attribute.

String Array

The list of data will be stored in a string attribute.

Integer Array

The list of data will be stored in an integer attribute.

Float Array

The list of data will be stored in a float attribute.

Unpacked Attributes

This option will unpack a JSON object into individual attributes.

PDG Value Index

This specifies the index of the work item attribute’s list to store the extracted value in.

Examples

example_top_jsoninput Example for JSON Input TOP node

This example demonstrates how to use json input node to create workitems based on information contained in json files.

See also

TOP nodes