Allow a single node pipeline (e.g. summarizer) to be created as a YAML file - which would allow for Document input.

[TuanaCelik]

I can imagine a use-case where for example you want to create a single node pipeline with just a Summarizer.

The problem I see here is that the Summarizer expects a list of Documents. Which makes creating a pipeline less intuitive as a pipeline expects 'File' or 'Query' as input.

The code below currently works:

summarizer = TransformersSummarizer(model_name_or_path="google/pegasus-xsum")
pipeline.add_node(name="Summarizer", component=summarizer, inputs=["Query"])
summary = pipeline.run(documents=[Document(request_data['text'])])

But given the Summarizer actually expects a list of documents, the second line there is a bit un-intuitive.

I saved the above pipeline to a YAML file which resulted in the following:

components:
- name: Summarizer
  params: {}
  type: TransformersSummarizer
pipelines:
- name: query
  nodes:
  - inputs:
    - Query
    name: Summarizer
  type: Pipeline
version: 1.2.0

A simple work-around might be to have a pipeline that converts Query to Document?

Basically what I'm trying to achieve is a demo which allows people to paste a piece of text, press play and be given a summary. This works by just calling '.predict()' but doesn't work great if you want to go down the 'pipelines' route.

[TuanaCelik]

Note: When trying to load this pipeline from YAML I get the following error: The node None is not in the graph.

I checked the pipeline by looking at pipeline.graph.nodes which turns up empty:

pipeline.load_from_yaml(Path("./pipeline/summarizer_pipeline.yaml"), pipeline_name='query')
print(f"Loaded pipeline nodes: {pipeline.graph.nodes}")

Result: Loaded pipeline nodes: []

We looked at this with @ZanSara and it seems like this might be resolved with her PR that's coming up

[bfgray3]

@TuanaCelik i am interested in using a single-node pipeline defined in yaml through the REST API. i dumped my pipeline to yaml and got a similar result as you show above except i had no type: Pipeline. is sending Documents in through the API possible?

[ZanSara]

Addressed by the Pipeline refactoring (https://github.com/deepset-ai/haystack/pull/4284), so closing this thread.