Add docs for GNN import and export

pages/advanced-algorithms/available-algorithms.mdx

@@ -74,6 +74,7 @@ If you want to know more and learn how this affects you, read our [announcement]
 
 | Algorithms                                                                                        | Lang   | Description                                                                                                                                               |
 |---------------------------------------------------------------------------------------------------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------------------|
+| [gnn](/advanced-algorithms/available-algorithms/gnn)                                              | Python | Export and import graph data in PyTorch Geometric (PyG) and TensorFlow GNN (TF-GNN) formats for GNN training pipelines.                                  |
 | [link_prediction with GNN](/advanced-algorithms/available-algorithms/gnn_link_prediction)         | Python | Module for predicting links in the graph by using graph neural networks.                                                                                  |
 | [node_classification with GNN](/advanced-algorithms/available-algorithms/gnn_node_classification) | Python | Graph neural network-based node classification module                                                                                                     |
 | [node2vec](/advanced-algorithms/available-algorithms/node2vec)                                    | Python | An algorithm for calculating node embeddings on static graph.                                                                                             |

pages/advanced-algorithms/available-algorithms/_meta.ts

@@ -21,6 +21,7 @@ export default {
   "elasticsearch_synchronization": "elasticsearch_synchronization",
   "embeddings": "embeddings",
   "export_util": "export_util",
+  "gnn": "gnn",
   "gnn_link_prediction": "gnn_link_prediction",
   "gnn_node_classification": "gnn_node_classification",
   "graph_analyzer": "graph_analyzer",

pages/advanced-algorithms/available-algorithms/gnn.mdx

@@ -0,0 +1,285 @@
+---
+title: gnn
+description: Export and import graph data in PyTorch Geometric (PyG) and TensorFlow GNN (TF-GNN) formats. Enables GNN training pipelines by converting Memgraph graphs to framework-native JSON representations and writing back inference results.
+---
+
+import { Callout } from 'nextra/components'
+import { Cards } from 'nextra/components'
+import GitHub from '/components/icons/GitHub'
+
+# gnn
+
+GNN integration module for Memgraph. Provides export/import procedures for
+**[PyTorch Geometric (PyG)](https://pytorch-geometric.readthedocs.io/en/latest/)** and **[TensorFlow GNN (TF-GNN)](https://github.com/tensorflow/gnn)** formats. All
+exports produce a single JSON string that can be deserialized on the client side
+and fed into the respective framework. 
+
+Typical workflow:
+
+1. **Export** – extract the graph (or a subgraph) from Memgraph into a
+   JSON representation that PyG or TF-GNN can consume directly.
+
+2. **Train / Infer** – use the exported data in your GNN pipeline outside
+   Memgraph.
+
+3. **Import** – write new nodes and relationships back into Memgraph from
+   the framework's output, or update existing nodes with inference results.
+
+<Cards>
+  <Cards.Card
+    icon={<GitHub />}
+    title="Source code"
+    href="https://github.com/memgraph/memgraph/blob/master/mage/python/gnn.py"
+  />
+</Cards>
+
+| Trait               | Value      |
+| ------------------- | ---------- |
+| **Module type**     | module     |
+| **Implementation**  | Python     |
+| **Parallelism**     | sequential |
+
+## Procedures
+
+### `pyg_export()`
+
+Exports the current graph to a JSON string in **PyTorch Geometric** format.
+
+The JSON payload contains:
+- `edge_index` – source and destination index arrays.
+- `x` – node feature matrix (when `node_property_names` is provided).
+- `edge_attr` – edge feature matrix (when `edge_property_names` is provided).
+- `y` – node labels (when `node_label_property` is provided).
+- `num_nodes` – total number of nodes.
+- `node_id_mapping` / `idx_to_node_id` – bidirectional mapping between
+  Memgraph internal IDs and PyG indices (used for write-back).
+- `labels` – original node labels.
+- `edge_types` – original relationship types.
+
+{<h4 className="custom-header"> Input: </h4>}
+
+- `node_property_names: List[string] (default = null)` ➡ Node properties to
+  include in the feature matrix `x`. Numeric properties are cast to floats;
+  list properties are flattened.
+- `edge_property_names: List[string] (default = null)` ➡ Edge properties to
+  include in `edge_attr`.
+- `node_label_property: string (default = null)` ➡ Node property to use as
+  the target label vector `y`.
+
+{<h4 className="custom-header"> Output: </h4>}
+
+- `json_data: string` ➡ A JSON string representing the graph in PyG format.
+
+{<h4 className="custom-header"> Usage: </h4>}
+
+Export features `feat` and edge attribute `weight`, with `class` as the
+target label:
+
+```cypher
+CALL gnn.pyg_export(["feat"], ["weight"], "class")
+YIELD json_data
+RETURN json_data;
+```
+
+Export with no features (topology only):
+
+```cypher
+CALL gnn.pyg_export()
+YIELD json_data
+RETURN json_data;
+```
+
+---
+
+### `pyg_import()`
+
+Imports data from a PyG JSON string into Memgraph. Supports two modes:
+
+- **Create mode** (default) – creates new nodes and relationships.
+- **Update mode** (`update_existing = true`) – uses the `idx_to_node_id`
+  mapping in the JSON payload to find existing Memgraph nodes and sets
+  properties on them. This is the typical *export → inference → write-back*
+  workflow.
+
+{<h4 className="custom-header"> Input: </h4>}
+
+- `json_data: string` ➡ JSON string previously produced by `pyg_export()` (or
+  any compatible PyG-format JSON).
+- `default_node_label: string (default = "PyGNode")` ➡ Label assigned to
+  created nodes when no label information is present in the JSON.
+- `default_edge_type: string (default = "CONNECTS")` ➡ Relationship type
+  assigned to created relationships when no type information is present.
+- `node_property_names: List[string] (default = null)` ➡ Names to assign
+  to individual feature columns when importing the feature matrix `x`.
+- `edge_property_names: List[string] (default = null)` ➡ Names to assign
+  to individual edge-attribute columns when importing `edge_attr`.
+- `update_existing: boolean (default = false)` ➡ When `true`, existing nodes
+  are updated instead of creating new ones.
+
+{<h4 className="custom-header"> Output: </h4>}
+
+- `nodes_created: integer` ➡ Number of nodes created (0 in update mode).
+- `edges_created: integer` ➡ Number of relationships created (0 in update mode).
+- `nodes_updated: integer` ➡ Number of existing nodes updated (0 in create mode).
+
+{<h4 className="custom-header"> Usage: </h4>}
+
+**Roundtrip example** – export from the graph and import as new nodes:
+
+```cypher
+CALL gnn.pyg_export(["feat"], ["weight"], "class")
+YIELD json_data
+WITH json_data
+CALL gnn.pyg_import(json_data, "Imported", "IMP", ["feat"], ["weight"])
+YIELD nodes_created, edges_created
+RETURN nodes_created, edges_created;
+```
+
+**Write-back example** – update existing nodes with predictions after
+inference:
+
+```cypher
+CALL gnn.pyg_import($json_data, "Node", "EDGE", ["prediction"], null, true)
+YIELD nodes_updated
+RETURN nodes_updated;
+```
+
+<Callout type="info">
+In update mode the procedure uses the `idx_to_node_id` mapping inside the JSON
+payload to look up existing vertices by their Memgraph internal ID. Make sure
+the JSON was originally exported from the same database.
+</Callout>
+
+---
+
+### `tf_export()`
+
+Exports the current graph to a JSON string in **TF-GNN** format.
+
+The JSON payload contains:
+- `schema` – describes node sets, edge sets and their feature schemas
+  (dtypes and shapes), matching the TF-GNN `GraphSchema` structure.
+- `graph` – the actual graph data with feature values, sizes and adjacency
+  information.
+
+{<h4 className="custom-header"> Input: </h4>}
+
+- `node_property_names: List[string] (default = null)` ➡ Node properties to
+  include as node-set features.
+- `edge_property_names: List[string] (default = null)` ➡ Edge properties to
+  include as edge-set features.
+- `node_set_name: string (default = "node")` ➡ Name of the node set in the
+  TF-GNN schema.
+- `edge_set_name: string (default = "edge")` ➡ Name of the edge set in the
+  TF-GNN schema.
+
+{<h4 className="custom-header"> Output: </h4>}
+
+- `json_data: string` ➡ A JSON string representing the graph in TF-GNN format.
+
+{<h4 className="custom-header"> Usage: </h4>}
+
+Export with node property `score` and edge property `weight`:
+
+```cypher
+CALL gnn.tf_export(["score"], ["weight"])
+YIELD json_data
+RETURN json_data;
+```
+
+Specify custom set names:
+
+```cypher
+CALL gnn.tf_export(["score"], ["weight"], "items", "similarities")
+YIELD json_data
+RETURN json_data;
+```
+
+---
+
+### `tf_import()`
+
+Imports data from a TF-GNN JSON string into Memgraph, creating new nodes
+and relationships.
+
+{<h4 className="custom-header"> Input: </h4>}
+
+- `json_data: string` ➡ JSON string previously produced by `tf_export()` (or
+  any compatible TF-GNN-format JSON).
+- `default_node_label: string (default = "TfGnnNode")` ➡ Label assigned to
+  created nodes when no label information is present.
+- `default_edge_type: string (default = "CONNECTS")` ➡ Relationship type
+  assigned to created relationships when no type information is present.
+
+{<h4 className="custom-header"> Output: </h4>}
+
+- `nodes_created: integer` ➡ Number of nodes created.
+- `edges_created: integer` ➡ Number of relationships created.
+
+{<h4 className="custom-header"> Usage: </h4>}
+
+**Roundtrip example** – export and re-import:
+
+```cypher
+CALL gnn.tf_export(["score"], ["weight"])
+YIELD json_data
+WITH json_data
+CALL gnn.tf_import(json_data, "TfNode", "TF_EDGE")
+YIELD nodes_created, edges_created
+RETURN nodes_created, edges_created;
+```
+
+---
+
+## Example
+
+The following end-to-end example shows how to move graph data through a PyG
+training pipeline.
+
+**1. Create sample data:**
+
+```cypher
+CREATE (a:Person {feat: [1.0, 2.0], age: 30, class: 0})
+  -[:KNOWS {weight: 0.5}]->
+       (b:Person {feat: [3.0, 4.0], age: 25, class: 1})
+  -[:KNOWS {weight: 0.8}]->
+       (c:Person {feat: [5.0, 6.0], age: 35, class: 0});
+```
+
+**2. Export to PyG format:**
+
+```cypher
+CALL gnn.pyg_export(["feat"], ["weight"], "class")
+YIELD json_data
+RETURN json_data;
+```
+
+**3. Use the JSON payload in Python (client-side):**
+
+```python
+import json
+import torch
+from torch_geometric.data import Data
+
+# result is the json_data string returned by Memgraph
+pyg_dict = json.loads(result)
+
+data = Data(
+    x=torch.tensor(pyg_dict["x"], dtype=torch.float),
+    edge_index=torch.tensor(pyg_dict["edge_index"], dtype=torch.long),
+    edge_attr=torch.tensor(pyg_dict["edge_attr"], dtype=torch.float),
+    y=torch.tensor(pyg_dict["y"], dtype=torch.long),
+)
+# Train your model ...
+```
+
+**4. Write predictions back to Memgraph:**
+
+After inference, update your JSON payload with the predictions and call
+`pyg_import` with `update_existing` set to `true`:
+
+```cypher
+CALL gnn.pyg_import($updated_json, "Person", "KNOWS", ["prediction"], null, true)
+YIELD nodes_updated
+RETURN nodes_updated;
+```