Step-by-Step Guides

FlowRunner Component

FlowRunner
Component

FlowRunner Component

The CustomComponent class allows us to create components that interact with Langflow itself. In this example, we will make a component that runs other flows available in "My Collection".

We will cover how to:

List Collection flows using the list_flows method.
Load a flow using the load_flow method.
Configure a dropdown input field using the options parameter.

The typical structure of a Custom Component is composed of display_name and description attributes, build and build_config methods.

from langflow import CustomComponent


class MyComponent(CustomComponent):
    display_name = "Custom Component"
    description = "This is a custom component"

    def build_config(self):
        ...

    def build(self):
        ...

Let's start by defining our component's display_name and description.

# from langflow import CustomComponent


class FlowRunner(CustomComponent):
    display_name = "Flow Runner"
    description = "Run other flows"

#    def build_config(self):
#        ...

#     def build(self):
#         ...

Second, we will import Document from the langchain.schema module. This will be the return type of the build method.

# from langflow import CustomComponent
from langchain.schema import Document

# class FlowRunner(CustomComponent):
#     display_name = "Flow Runner"
#     description = "Run other flows"

#    def build_config(self):
#        ...

#     def build(self):
#         ...

Now, let's add the parameters and the return type to the build method. The parameters added are:

flow_name is the name of the flow we want to run.
document is the input document to be passed to that flow.
- Since Document is a Langchain type, it will add an input handle to the component (see more).

# from langflow import CustomComponent
from langchain.schema import Document

# class FlowRunner(CustomComponent):
#     display_name = "Flow Runner"
#     description = "Run other flows"

#    def build_config(self):
#        ...

   def build(self, flow_name: str, document: Document) -> Document:
        ...

We can now start writing the build method. Let's list available flows in "My Collection" using the list_flows method.

# from langflow import CustomComponent
# from langchain.schema import Document

# class FlowRunner(CustomComponent):
#     display_name = "Flow Runner"
#     description = "Run other flows"

#    def build_config(self):
#        ...

#    def build(self, flow_name: str, document: Document) -> Document:
        # List the flows
        flows = self.list_flows()

CAUTION

From version 0.4.0, names are unique, which was not the case in previous versions. This might lead to unexpected results if using flows with the same name.

And retrieve a flow that matches the selected name (we'll make a dropdown input field for the user to choose among flow names).

# from langflow import CustomComponent
# from langchain.schema import Document

# class FlowRunner(CustomComponent):
#     display_name = "Flow Runner"
#     description = "Run other flows"

#    def build_config(self):
#        ...

#    def build(self, flow_name: str, document: Document) -> Document:
        # List the flows
#       flows = self.list_flows()
        # Get the flow that matches the selected name
        # You can also get the flow by id
        # using self.get_flow(flow_id=flow_id)
        tweaks = {}
#       flow = self.get_flow(flow_name=flow_name, tweaks=tweaks)

You can load this flow using get_flow and set a tweaks dictionary to customize it. Find more about tweaks in our features guidelines.

from langflow import CustomComponent
from langchain.schema import Document


class FlowRunner(CustomComponent):
    display_name = "Flow Runner"
    description = "Run other flows using a document as input."

    def build_config(self):
        ...

    def build(self, flow_name: str, document: Document) -> Document:
        # List the flows
        flows = self.list_flows()
        # Get the flow that matches the selected name
        # You can also get the flow by id
        # using self.get_flow(flow_id=flow_id)
        tweaks = {}
        flow = self.get_flow(flow_name=flow_name, tweaks=tweaks)

We are using a Document as input because it is a straightforward way to pass text data in Langflow (specifically because you can connect it to many loaders). Generally, a flow will take a string or a dictionary as input because that's what LangChain components expect. In case you are passing a dictionary, you need to build it according to the needs of the flow you are using.

The content of a document can be extracted using the page_content attribute, which is a string, and passed as an argument to the selected flow.

from langflow import CustomComponent
from langchain.schema import Document


class FlowRunner(CustomComponent):
    display_name = "Flow Runner"
    description = "Run other flows using a document as input."

    def build_config(self):
        ...

    def build(self, flow_name: str, document: Document) -> Document:
        # List the flows
        flows = self.list_flows()
        # Get the flow that matches the selected name
        # You can also get the flow by id
        # using self.get_flow(flow_id=flow_id)
        tweaks = {}
        flow = self.get_flow(flow_name=flow_name, tweaks=tweaks)
        # Get the page_content from the document
        if document and isinstance(document, list):
            document = document[0]
        page_content = document.page_content
        # Use it in the flow
        result = flow(page_content)
        return Document(page_content=str(result))

CAUTION

Make sure that the field type is str and options values are strings.

Finally, we can add field customizations through the build_config method. Here we added the options key to make the flow_name field a dropdown menu. Check out the custom component reference for a list of available keys.

# from langchain.schema import Document


# class FlowRunner(CustomComponent):
#     display_name = "Flow Runner"
#     description = "Run other flows using a document as input."

    def build_config(self):
        flows = self.list_flows()
        flow_names = [f.name for f in flows]
        return {"flow_name": {"options": flow_names,
                                "display_name": "Flow Name",
        },
               "document": {"display_name": "Document"}
        }

#     def build(self, flow_name: str, document: Document) -> Document:
        # List the flows
#         flows = self.list_flows()
        # Get the flow that matches the selected name
        # You can also get the flow by id
        # using self.get_flow(flow_id=flow_id)

Done! This is what our script and custom component looks like:

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FlowRunner Component

FlowRunnerComponent

FlowRunner Component

FlowRunner
Component