langchain[patch]: Allow OpenSearch Query Translator to correctly work with Date types (#16022)

**Description:**

Fixes an issue where the Date type in an OpenSearch Self Querying
Retriever would fail to generate a valid query

**Issue:**
https://github.com/langchain-ai/langchain/issues/14225

libs/langchain/langchain/retrievers/self_query/opensearch.py

@@ -58,9 +58,23 @@ class OpenSearchTranslator(Visitor):
             Comparator.GT,
             Comparator.GTE,
         ]:
+            if isinstance(comparison.value, dict):
+                if "date" in comparison.value:
                     return {
                         "range": {
-                    field: {self._format_func(comparison.comparator): comparison.value}
+                            field: {
+                                self._format_func(
+                                    comparison.comparator
+                                ): comparison.value["date"]
+                            }
+                        }
+                    }
+            else:
+                return {
+                    "range": {
+                        field: {
+                            self._format_func(comparison.comparator): comparison.value
+                        }
                     }
                 }
 
@@ -70,8 +84,13 @@ class OpenSearchTranslator(Visitor):
                     field: {"value": comparison.value}
                 }
             }
+
         field = f"{field}.keyword" if isinstance(comparison.value, str) else field
 
+        if isinstance(comparison.value, dict):
+            if "date" in comparison.value:
+                comparison.value = comparison.value["date"]
+
         return {self._format_func(comparison.comparator): {field: comparison.value}}
 
     def visit_structured_query(
@@ -81,4 +100,5 @@ class OpenSearchTranslator(Visitor):
             kwargs = {}
         else:
             kwargs = {"filter": structured_query.filter.accept(self)}
+
         return structured_query.query, kwargs

libs/langchain/tests/unit_tests/retrievers/self_query/test_opensearch.py

@@ -85,3 +85,90 @@ def test_visit_structured_query() -> None:
     )
     actual = DEFAULT_TRANSLATOR.visit_structured_query(structured_query)
     assert expected == actual
+
+
+def test_visit_structured_query_with_date_range() -> None:
+    query = "Who was the president of France in 1995?"
+    operation = Operation(
+        operator=Operator.AND,
+        arguments=[
+            Comparison(comparator=Comparator.EQ, attribute="foo", value="20"),
+            Operation(
+                operator=Operator.AND,
+                arguments=[
+                    Comparison(
+                        comparator=Comparator.GTE,
+                        attribute="timestamp",
+                        value={"date": "1995-01-01", "type": "date"},
+                    ),
+                    Comparison(
+                        comparator=Comparator.LT,
+                        attribute="timestamp",
+                        value={"date": "1996-01-01", "type": "date"},
+                    ),
+                ],
+            ),
+        ],
+    )
+    structured_query = StructuredQuery(query=query, filter=operation, limit=None)
+    expected = (
+        query,
+        {
+            "filter": {
+                "bool": {
+                    "must": [
+                        {"term": {"metadata.foo.keyword": "20"}},
+                        {
+                            "bool": {
+                                "must": [
+                                    {
+                                        "range": {
+                                            "metadata.timestamp": {"gte": "1995-01-01"}
+                                        }
+                                    },
+                                    {
+                                        "range": {
+                                            "metadata.timestamp": {"lt": "1996-01-01"}
+                                        }
+                                    },
+                                ]
+                            }
+                        },
+                    ]
+                }
+            }
+        },
+    )
+    actual = DEFAULT_TRANSLATOR.visit_structured_query(structured_query)
+    assert expected == actual
+
+
+def test_visit_structured_query_with_date() -> None:
+    query = "Who was the president of France on 1st of January 1995?"
+    operation = Operation(
+        operator=Operator.AND,
+        arguments=[
+            Comparison(comparator=Comparator.EQ, attribute="foo", value="20"),
+            Comparison(
+                comparator=Comparator.EQ,
+                attribute="timestamp",
+                value={"date": "1995-01-01", "type": "date"},
+            ),
+        ],
+    )
+    structured_query = StructuredQuery(query=query, filter=operation, limit=None)
+    expected = (
+        query,
+        {
+            "filter": {
+                "bool": {
+                    "must": [
+                        {"term": {"metadata.foo.keyword": "20"}},
+                        {"term": {"metadata.timestamp": "1995-01-01"}},
+                    ]
+                }
+            }
+        },
+    )
+    actual = DEFAULT_TRANSLATOR.visit_structured_query(structured_query)
+    assert expected == actual