
Name	OutputAdapter
Folder path	/converters/
Most common position in a pipeline	Flexible
Mandatory input variables	“**kwargs”: Input variables to be used in Jinja expression
Output variables	The output is specified under the “output” key dictionary

Overview

To use OutputAdapter, you need to specify the adaptation rule that includes:

template: A Jinja template string that defines how to adapt the input data.
output_type: The type of the output data (such as str, List[int]..). This doesn't change the actual output type and is only needed to validate connection with other components.
custom_filters: An optional dictionary of custom Jinja filters to be used in the template.

📘
Output Types
For security reasons, the OutputAdapter can only return the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, None and Ellipsis (...), as well as any combination of these structures. This means that Haystack classes such as ChatMessage, Document, or Answer can't be used as output types.

Usage

On its own

This component is primarily meant to be used in pipelines.

In this example, OutputAdapter simply outputs the content field of the first document in the arrays of documents:

from haystack import Document
from haystack.components.converters import OutputAdapter

adapter = OutputAdapter(template="{{ documents[0].content }}", output_type=str)
input_data = {"documents": [Document(content="Test content")]}
expected_output = {"output": "Test content"}
assert adapter.run(**input_data) == expected_output

In a pipeline

The example below demonstrates a straightforward pipeline that uses the OutputAdapter to capitalize the first document in the list. If needed, you can also utilize the predefined Jinja filters.

from haystack import Pipeline, component, Document
from haystack.components.converters import OutputAdapter

@component
class DocumentProducer:
    @component.output_types(documents=dict)
    def run(self):
        return {"documents": [Document(content="haystack")]}

pipe = Pipeline()
pipe.add_component(
    name="output_adapter",
    instance=OutputAdapter(template="{{ documents[0].content | capitalize}}", output_type=str),
)
pipe.add_component(name="document_producer", instance=DocumentProducer())
pipe.connect("document_producer", "output_adapter")
result = pipe.run(data={})

assert result["output_adapter"]["output"] == "Haystack"

You can also define your own custom filters, which can then be added to an OutputAdapter instance through its init method and used in templates. Here’s an example of this approach:


from haystack import Pipeline, component, Document
from haystack.components.converters import OutputAdapter

def reverse_string(s):
    return s[::-1]

@component
class DocumentProducer:
    @component.output_types(documents=dict)
    def run(self):
        return {"documents": [Document(content="haystack")]}

pipe = Pipeline()
pipe.add_component(
    name="output_adapter",
    instance=OutputAdapter(template="{{ documents[0].content | reverse_string}}",
                           output_type=str,
                           custom_filters={"reverse_string": reverse_string}))

pipe.add_component(name="document_producer", instance=DocumentProducer())
pipe.connect("document_producer", "output_adapter")
result = pipe.run(data={})

assert result["output_adapter"]["output"] == "kcatsyah"

Overview

📘Output Types

Usage

On its own

In a pipeline

📘
Output Types