community[patch]: Implement Unique ID Enforcement in FAISS (#17244)

**Description:**
Implemented unique ID validation in the FAISS component to ensure all
document IDs are distinct. This update resolves issues related to
non-unique IDs, such as inconsistent behavior during deletion processes.

libs/community/langchain_community/vectorstores/faiss.py

@@ -190,6 +190,9 @@ class FAISS(VectorStore):
         _len_check_if_sized(documents, embeddings, "documents", "embeddings")
         _len_check_if_sized(documents, ids, "documents", "ids")
 
+        if ids and len(ids) != len(set(ids)):
+            raise ValueError("Duplicate ids found in the ids list.")
+
         # Add to the index.
         vector = np.array(embeddings, dtype=np.float32)
         if self._normalize_L2:

libs/community/tests/unit_tests/vectorstores/test_faiss.py

@@ -774,3 +774,15 @@ async def test_async_delete() -> None:
     result = await docsearch.asimilarity_search("bar", k=2)
     assert sorted([d.page_content for d in result]) == ["baz", "foo"]
     assert docsearch.index_to_docstore_id == {0: ids[0], 1: ids[2]}
+
+
+@pytest.mark.requires("faiss")
+def test_faiss_with_duplicate_ids() -> None:
+    """Test whether FAISS raises an exception for duplicate ids."""
+    texts = ["foo", "bar", "baz"]
+    duplicate_ids = ["id1", "id1", "id2"]
+
+    with pytest.raises(ValueError) as exc_info:
+        FAISS.from_texts(texts, FakeEmbeddings(), ids=duplicate_ids)
+
+    assert "Duplicate ids found in the ids list." in str(exc_info.value)