JSONUpdater

Input features contain the JSON documents to be modified. The documents can be contained in an attribute, entered directly into the transformer, or contained in a file referenced by an attribute value.

For each feature which enters this input port, each of the updates listed in the transformer will be executed on each document which entered via the Document input port. These features will contain the attributes values which are used in the document updates.

The Document input features will be output through this port. These features will contain the updated document, which will be stored in the attribute named in the Result Attribute parameter. The updated document will always be saved as a utf-8 encoded attribute value, regardless of the encoding of the original document.

This parameter is used to specify which update features will modify a document. When this parameter is set to a list of attributes, Document features will only be modified by Update features that share the same values for these attributes. The document will be modified by all of the update features with the same attribute values. Note that a document will not be updated if no Update features with the same values for the “group by” attributes are provided to the transformer.

Process At End (Blocking): This is the default behavior. Processing will only occur in this transformer once all input is present.

Process When Group Changes (Advanced): This transformer will process input groups in order. Changes of the value of the Group By parameter on the input stream will trigger processing on the currently accumulating group. This may improve overall speed (particularly with multiple, equally-sized groups), but could cause undesired behavior if input groups are not truly ordered.

Considerations for Using Group By

There are two typical reasons for using Process When Group Changes (Advanced) . The first is incoming data that is intended to be processed in groups (and is already so ordered). In this case, the structure dictates Group By usage - not performance considerations.

The second possible reason is potential performance gains.

Performance gains are most likely when the data is already sorted (or read using a SQL ORDER BY statement) since less work is required of FME. If the data needs ordering, it can be sorted in the workspace (though the added processing overhead may negate any gains).

Sorting becomes more difficult according to the number of data streams. Multiple streams of data could be almost impossible to sort into the correct order, since all features matching a Group By value need to arrive before any features (of any feature type or dataset) belonging to the next group. In this case, using Group By with Process At End (Blocking) may be the equivalent and simpler approach.

Note: Multiple feature types and features from multiple datasets will not generally naturally occur in the correct order.

As with many scenarios, testing different approaches in your workspace with your data is the only definitive way to identify performance gains.

This parameter is used to specify the type of JSON document which is to be modified. The JSON may come from the input features (Parameter Value: Text or Attribute), or it may come from an external file. (Parameter Value: JSON File)

When the JSON Input parameter is set to ‘Text or Attribute’, this parameter is used to specify the JSON text. The parameter may be set to an attribute value, or the JSON document may be entered into the parameter directly.

When the JSON Input parameter is set to ‘JSON File’, this parameter is used to specify the location of the file. The file path may be entered directly into the parameter, or the path may come from an attribute value.

This parameter specifies the type of modification to apply to the XML document. The possible updates are:

This parameter is used to identify the JSON object or array which is to be updated. For updates which modify a specific object key or array index, the key / index is identified using the ‘Object/Array Index’ parameter.

JSON paths use a simple text syntax to trace a route through a JSON document, from the top level object or array, down to the object or array which is being modified.

All JSON documents must have a single object or array as the root value. In a JSON path, this root value is identified by the ‘json’ keyword. Thus, every JSON path begins with this keyword. Square bracket syntax is used to identify each level of the path.

An integer can be used to identify a position within an array:

• json[0] – If the root value is an array, this path refers to the first value in the array. If the root value is an object, this path will not resolve to any value.
• json[4] – If the root value is an array, this path refers to the fifth value in the array.

A quoted string can be used to refer to the value of an object key:

• json["location"] – If the root value is an object, this path refers to the value of the ‘location’ key in the object. If the root value is an array, this path will not resolve to any value.
• json["features"] – Refers to the value of the ‘features’ key in the root object.

These indices may be repeated, to have the path go deeper into the JSON document. It is important to know the structure of the document, so that the types of indices (object or array) are correct.

• json[0]["location"] – This path refers to the ‘location’ object key in the first element in the root array.
• json["features"][0][ "location"] – This path refers to the value of the ‘location key in the first item in the ‘features’ array of the root object. For example, this could apply to the following (incomplete) document:

  {

  "features" : [

  { "location” : { ... } }

  ]

  }

A wildcard may be used to refer to all elements of an array, or all values in an object. A * character is used to denote a wildcard.

• json[*] – If the root value is an array, this path refers to all values in the array. If the root value is an object, this path refers to the values of all keys in the object.
• json[*]["location"] – This path refers to the ‘location’ key of all child values of the root object or array.
• json["features"][*] – This path refers to all the values contained in the value of the ‘features’ key in the root object.

In order to use an attribute value in a JSON path, the @Value FME function should be used. If the attribute value is an object key, the @Value function should be enclosed in quotes.

• json[@Value(index)] – This path refers to the item in the root array at the position indicated by the ‘index’ attribute.
• json["@Value(key)"] – This path refers to the object value whose key is named in the ‘key’ attribute.

Note: The @Value() functions used in the path parameter will apply to the Update feature being processed, not the Document feature that is being updated

This parameter is used to specify the specific object key / array index whose value is to be inserted/removed/modified.

For object updates, this value of this parameter should be a string, which will be interpreted as an object key. Quotes are NOT required around the string in this parameter.

For array updates, the value of this parameter should be an integer. Note that array indices start at 0.

This parameter is used to indicate how the value of the Value parameter should be interpreted. The effects of the different values of this parameter are explained in the description of the Value parameter. In general, this parameter should be set to Plain Text if the transformer is intended to insert text content into the document, while it should be set to JSON/XQuery if the transformer is intended to insert JSON objects or arrays into the document, or if the value is being produced through XQuery function calls.

This parameter is used to specify the new values that should be inserted into the document. If the Value Type parameter is set to Plain Text, the contents of this parameter will be encoded for safe use in an XML document. That is, double quotes will be escaped as \", backslashes will be escaped as \\, and so on.

If the Value Type parameter is set to JSON/XQuery, the contents of this parameter will be interpreted as an XQuery expression. This allows the insertion of JSON values elements into the document. Also, this allows the use of the FME XQuery functions. For example, a JSON Template (for example, from the JSONTemplater transformer) could be entered as the parameter value. It would then be evaluated before being inserted into the document.

Note: Any FME XQuery functions used in the new value will access the Update feature, not the Document feature.

This parameter specifies whether or not Workbench should try to validate the attribute names which are passed to any XQuery functions used in the Value column.

This parameter specifies the attribute to which the updated JSON document will be written. The default is _result.