Add transalor

langchain_postgres/__init__.py

@@ -1,6 +1,7 @@
 from importlib import metadata
 
 from langchain_postgres.chat_message_histories import PostgresChatMessageHistory
+from langchain_postgres.translator import PGVectorTranslator
 from langchain_postgres.vectorstores import PGVector
 
 try:
@@ -13,4 +14,5 @@
     "__version__",
     "PostgresChatMessageHistory",
     "PGVector",
+    "PGVectorTranslator",
 ]

langchain_postgres/translator.py

@@ -0,0 +1,52 @@
+from typing import Dict, Tuple, Union
+
+from langchain_core.structured_query import (
+    Comparator,
+    Comparison,
+    Operation,
+    Operator,
+    StructuredQuery,
+    Visitor,
+)
+
+
+class PGVectorTranslator(Visitor):
+    """Translate `PGVector` internal query language elements to valid filters."""
+
+    allowed_operators = [Operator.AND, Operator.OR]
+    """Subset of allowed logical operators."""
+    allowed_comparators = [
+        Comparator.EQ,
+        Comparator.NE,
+        Comparator.GT,
+        Comparator.LT,
+        Comparator.IN,
+        Comparator.NIN,
+        Comparator.CONTAIN,
+        Comparator.LIKE,
+    ]
+    """Subset of allowed logical comparators."""
+
+    def _format_func(self, func: Union[Operator, Comparator]) -> str:
+        self._validate_func(func)
+        return f"${func.value}"
+
+    def visit_operation(self, operation: Operation) -> Dict:
+        args = [arg.accept(self) for arg in operation.arguments]
+        return {self._format_func(operation.operator): args}
+
+    def visit_comparison(self, comparison: Comparison) -> Dict:
+        return {
+            comparison.attribute: {
+                self._format_func(comparison.comparator): comparison.value
+            }
+        }
+
+    def visit_structured_query(
+        self, structured_query: StructuredQuery
+    ) -> Tuple[str, dict]:
+        if structured_query.filter is None:
+            kwargs = {}
+        else:
+            kwargs = {"filter": structured_query.filter.accept(self)}
+        return structured_query.query, kwargs

tests/unit_tests/test_imports.py

@@ -3,6 +3,7 @@
 EXPECTED_ALL = [
     "__version__",
     "PGVector",
+    "PGVectorTranslator",
     "PostgresChatMessageHistory",
 ]