[Docs] Treat delegated execution separately

docs/source/plugins/using_plugins.rst

@@ -594,8 +594,8 @@ operator can be invoked like so:
     dataset = foz.load_zoo_dataset("quickstart")
     compute_metadata = foo.get_operator("@voxel51/utils/compute_metadata")
 
-    # Schedule a delegated operation to (re)compute metadata
-    compute_metadata(dataset, overwrite=True, delegate=True)
+    # (Re)compute the dataset's metadata
+    compute_metadata(dataset, overwrite=True)
 
 .. note::
 
@@ -614,13 +614,11 @@ follows:
             sample_collection,
             overwrite=False,
             num_workers=None,
-            delegate=False,
         ):
             ctx = dict(view=sample_collection.view())
             params = dict(
                 overwrite=overwrite,
                 num_workers=num_workers,
-                delegate=delegate,
             )
             return foo.execute_operator(self.uri, ctx, params=params)
 
@@ -655,71 +653,63 @@ data, you can access it via the ``result`` property of the returned
         result = await op(...)
         print(result.result) # {...}
 
-.. _delegating-function-calls:
-
-Delegating function calls
--------------------------
+Requesting delegation
+~~~~~~~~~~~~~~~~~~~~~
 
-The
-`@voxel51/utils/delegate <https://github.com/voxel51/fiftyone-plugins/tree/main/plugins/utils>`_
-operator provides a general purpose utility for
-:ref:`delegating execution <delegated-operations>` of an arbitrary function
-call that can be expressed in any of the following forms:
+Operators that support :ref:`delegated execution <delegated-operations>` can
+support this via the `__call__()` syntax by passing the
+`request_delegation=True` flag to
+:func:`execute_operator() <fiftyone.operators.execute_operator>`.
 
--   Execute an arbitrary function: `fcn(*args, **kwargs)`
--   Apply a function to a dataset or view:
-    `fcn(dataset_or_view, *args, **kwargs)`
--   Call an instance method of a dataset or view:
-    `dataset_or_view.fcn(*args, **kwargs)`
-
-Here's some examples of delegating common tasks that can be expressed in the
-above forms:
+In fact, the
+`@voxel51/utils/compute_metadata <https://github.com/voxel51/fiftyone-plugins/tree/main/plugins/utils>`_
+operator does just that:
 
 .. code-block:: python
     :linenos:
 
-    import fiftyone as fo
-    import fiftyone.operators as foo
-    import fiftyone.zoo as foz
+    class ComputeMetadata(foo.Operator):
+        def __call__(
+            self,
+            sample_collection,
+            overwrite=False,
+            num_workers=None,
+            delegate=False,
+        ):
+            ctx = dict(view=sample_collection.view())
+            params = dict(
+                overwrite=overwrite,
+                num_workers=num_workers,
+            )
+            return foo.execute_operator(
+                self.uri,
+                ctx,
+                params=params,
+                request_delegation=delegate,
+            )
 
-    dataset = foz.load_zoo_dataset("quickstart")
-    delegate = foo.get_operator("@voxel51/utils/delegate")
+        def resolve_execution_options(self, ctx):
+            return foo.ExecutionOptions(
+                allow_delegated_execution=True,
+                allow_immediate_execution=True,
+            )
 
-    # Compute metadata
-    delegate("compute_metadata", dataset=dataset)
+which means that it can be invoked like so:
 
-    # Compute visualization
-    delegate(
-        "fiftyone.brain.compute_visualization",
-        dataset=dataset,
-        brain_key="img_viz",
-    )
+.. code-block:: python
+    :linenos:
 
-    # Export a view
-    delegate(
-        "export",
-        view=dataset.to_patches("ground_truth"),
-        export_dir="/tmp/patches",
-        dataset_type="fiftyone.types.ImageClassificationDirectoryTree",
-        label_field="ground_truth",
-    )
+    compute_metadata = foo.get_operator("@voxel51/utils/compute_metadata")
 
-    # Load the exported patches into a new dataset
-    delegate(
-        "fiftyone.Dataset.from_dir",
-        dataset_dir="/tmp/patches",
-        dataset_type="fiftyone.types.ImageClassificationDirectoryTree",
-        label_field="ground_truth",
-        name="patches",
-        persistent=True,
-    )
+    # Schedule a delegated operation to (re)compute metadata
+    compute_metadata(dataset, overwrite=True, delegate=True)
 
 .. _direct-operator-execution:
 
 Direct execution
 ----------------
 
-You can also programmatically execute any operator by directly calling
+You can programmatically execute any operator by directly calling
 :func:`execute_operator() <fiftyone.operators.execute_operator>`:
 
 .. code-block:: python
@@ -738,25 +728,11 @@ You can also programmatically execute any operator by directly calling
             dataset_type="COCO",
             labels_path=dict(absolute_path="/tmp/coco/labels.json"),
             label_field="ground_truth",
-            delegate=False,  # False: execute immediately, True: delegate
         )
     }
 
     foo.execute_operator("@voxel51/io/export_samples", ctx)
 
-In the above example, the `delegate=True/False` parameter controls whether
-execution happens immediately or is
-:ref:`delegated <operator-delegated-execution>` because the operator implements
-its
-:meth:`resolve_delegation() <fiftyone.operators.operator.Operator.resolve_delegation>`
-as follows:
-
-.. code-block:: python
-    :linenos:
-
-    def resolve_delegation(self, ctx):
-        return ctx.params.get("delegate", False)
-
 .. note::
 
     In general, to use
@@ -787,13 +763,12 @@ data, you can access it via the ``result`` property of the returned
         result = await foo.execute_operator("@an-operator/with-results", ctx)
         print(result.result)  # {...}
 
-.. _requesting-operator-delegation:
-
 Requesting delegation
----------------------
+~~~~~~~~~~~~~~~~~~~~~
 
-If an operation supports both immediate and delegated execution as specified
-either by its :ref:`configuration <operator-delegation-configuration>` or
+If an operation supports both immediate and
+:ref:`delegated execution <delegated-operations>` as specified either by its
+:ref:`configuration <operator-delegation-configuration>` or
 :ref:`execution options <operator-execution-options>`, you can request
 delegated execution by passing the `request_delegation=True` flag to
 :func:`execute_operator() <fiftyone.operators.execute_operator>`:
@@ -823,6 +798,65 @@ operator's input modal when executing it from within the App:
             delegation_target="overnight",
         )
 
+.. _delegating-function-calls:
+
+Delegating function calls
+-------------------------
+
+The
+`@voxel51/utils/delegate <https://github.com/voxel51/fiftyone-plugins/tree/main/plugins/utils>`_
+operator provides a general purpose utility for
+:ref:`delegating execution <delegated-operations>` of an arbitrary function
+call that can be expressed in any of the following forms:
+
+-   Execute an arbitrary function: `fcn(*args, **kwargs)`
+-   Apply a function to a dataset or view:
+    `fcn(dataset_or_view, *args, **kwargs)`
+-   Call an instance method of a dataset or view:
+    `dataset_or_view.fcn(*args, **kwargs)`
+
+Here's some examples of delegating common tasks that can be expressed in the
+above forms:
+
+.. code-block:: python
+    :linenos:
+
+    import fiftyone as fo
+    import fiftyone.operators as foo
+    import fiftyone.zoo as foz
+
+    dataset = foz.load_zoo_dataset("quickstart")
+    delegate = foo.get_operator("@voxel51/utils/delegate")
+
+    # Compute metadata
+    delegate("compute_metadata", dataset=dataset)
+
+    # Compute visualization
+    delegate(
+        "fiftyone.brain.compute_visualization",
+        dataset=dataset,
+        brain_key="img_viz",
+    )
+
+    # Export a view
+    delegate(
+        "export",
+        view=dataset.to_patches("ground_truth"),
+        export_dir="/tmp/patches",
+        dataset_type="fiftyone.types.ImageClassificationDirectoryTree",
+        label_field="ground_truth",
+    )
+
+    # Load the exported patches into a new dataset
+    delegate(
+        "fiftyone.Dataset.from_dir",
+        dataset_dir="/tmp/patches",
+        dataset_type="fiftyone.types.ImageClassificationDirectoryTree",
+        label_field="ground_truth",
+        name="patches",
+        persistent=True,
+    )
+
 .. _delegated-operations:
 
 Delegated operations
@@ -893,7 +927,7 @@ delegated operations and execute them serially in its process.
 
 You must also ensure that the
 :ref:`allow_legacy_orchestrators <configuring-fiftyone>` config flag is set
-in the environment where you run the App, e.g. by setting:
+in the environment where you run the App/SDK, e.g. by setting:
 
 .. code-block:: shell
 

fiftyone/operators/executor.py

@@ -261,12 +261,13 @@ async def execute_or_delegate_operator(
             ctx.request_params["delegated"] = True
             metadata = {"inputs_schema": None, "outputs_schema": None}
 
-            try:
-                metadata["inputs_schema"] = inputs.to_json()
-            except Exception as e:
-                logger.warning(
-                    f"Failed to resolve inputs schema for the operation: {str(e)}"
-                )
+            if inputs is not None:
+                try:
+                    metadata["inputs_schema"] = inputs.to_json()
+                except Exception as e:
+                    logger.warning(
+                        f"Failed to resolve inputs schema for the operation: {str(e)}"
+                    )
 
             op = DelegatedOperationService().queue_operation(
                 operator=operator.uri,