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Version: v0.17.0


Schemas are a way to ensure that your data (entities, arrays or streams) have a particular structure, for example you can control which properties are present and what types they have.

Steps which use JSON Schema

  • CreateSchema creates a schema from an array of entities.

The step will produce the most restrictive schema possible.

- CreateSchema [('Foo': 1), ('Foo': 2)]
| Log

Please note that this step is quite expensive so if you have a large array of entities you should use ArrayTake 100 to use only the first hundred entities to create the schema.

  • Transform tries to adjust entities so that they fit a schema.

This example transforms the 'Foo' value from a string to an integer.

- <schema> = FromJSON '{"type": "object", "properties": {"foo": {"type": "integer"}}}'
- <entities> = [('Foo': '1'), ('Foo': '2'), ('Foo': '3')]
- <results> = Transform <entities> <schema>
- <results> | ForEach (Log <>)

You can provide additional arguments to control how properties are transformed and what happends when there are errors.

  • Validate ensures that every entity in an array matches the schema

This example filters the entities to only those where 'Foo' is a multiple of 2.

You could change the Error Behavior to do act differently for elements which do not match.

- <schema> = FromJSON '{"type": "object", "properties": {"foo": {"type": "integer", "MultipleOf": 2}}}'
- <entities> = [('Foo': 1), ('Foo': 2), ('Foo': 3), ('Foo': 4)]
- <results> = Validate <entities> <schema> ErrorBehavior: 'Skip'
- <results> | ForEach (Log <>)

Error Behavior

In the Transform and Validate steps, when there are entities that fail validation, the output depends on the argument passed to the ErrorBehavior parameters.

The possible values for ErrorBehavior are:

FailStop at the first error that is encountered
ErrorEmit non-terminating error and filter out entities that fail validation
WarningEmit warning but do nothing
SkipFilter out entities but do not emit warning

Working with Regexes

You can use the pattern property to specify a regular expression that the property must match.

- <entities> = [('foo': 'abc'), ('foo': 'abc123')]
- <schema> = ( (type:'string', pattern: '\A[a-z]+\Z'))

# Use validate to filter out the entities which don't match the schema
- <validated> = <entities> | Validate <schema> ErrorBehavior: 'skip'

# Print the entities. Note that only the first is printed
- ForEach <validated> (Log Value: <>)

Working with Booleans

You can indicate a boolean property with type: boolean. The Transform step allows you to convert string values to booleans by specifying the BooleanTrueFormats and BooleanFalseFormats properties.

- <entities> = [('Name': 'abc', 'IsGood': 'yes'), ('Name': 'yes', IsGood: 'no')]
- <schema> = (properties: (Name: (type: 'string'), IsGood: (type: 'boolean')))

- <transformed> = <entities> | Transform <schema>
BooleanTrueFormats: 'yes'
BooleanFalseFormats: 'no'

#Print the entities. Note that only the first is printed
- ForEach <transformed> (Log Value: <>)

These properties can also take an Array<String> to indicate multiple string map to a boolean value or an Entity to specify different mappings for different properties.

Working with Dates

To specify that a property should be a date, use the type string and the format date-time

"properties": {
"Foo": {
"type": "string",
"format": "date-time"

Use can use the Transform step to change a string property which contains a date in a particular format to a DateTime.

The DateInputFormats Parameter of the Transform step lets you define either:

  • A string format to use for each date-time property
  • An Array<string> of possible formats to try for each date-time property
  • An entity mapping property names to either a string or Array<string> allowing you to define custom handling for each date-time property individually.
- <entities> = [(DayFirst: "13-12-1989",YearFirst: "1989/12/13"), (DayFirst: "20-02-2003", YearFirst: "2003-02-20")]
- <schema> = (properties: (DayFirst: (type: "string",format: "date-time"), YearFirst: (type: "string",format: "date-time")))
- <dateInputFormats> = (DayFirst: "dd-MM-yyyy", YearFirst: ["yyyy/MM/dd", "yyyy-MM-dd"])

- <transformed> = <entities> | Transform <schema> DateInputFormats: <dateInputFormats>

#Print both entities, note that each has it's dates in the same format
- ForEach <transformed> (Log Value: <>)

The Json Schema also provides date and time formats. Be careful with these as they will be checked by the Validate step but not transformed into by the Transform step.

Resources for JSON Schemas: