Fix SQLAlchemy truncating text when it is too big (#5206)

# Fixes SQLAlchemy truncating the result if you have a big/text column
with many chars.

SQLAlchemy truncates columns if you try to convert a Row or Sequence to
a string directly

For comparison:

- Before:
```[('Harrison', 'That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio ... (2 characters truncated) ... hat is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio That is my Bio ')]```

- After:
```[('Harrison', 'That is my Bio That is my Bio That is my Bio That is
my Bio That is my Bio That is my Bio That is my Bio That is my Bio That
is my Bio That is my Bio That is my Bio That is my Bio That is my Bio
That is my Bio That is my Bio That is my Bio That is my Bio That is my
Bio That is my Bio That is my Bio ')]```



## Who can review?

Community members can review the PR once tests pass. Tag
maintainers/contributors who might be interested:

I'm not sure who to tag for chains, maybe @vowelparrot ?

langchain/sql_database.py

@@ -5,14 +5,7 @@ import warnings
 from typing import Any, Iterable, List, Optional
 
 import sqlalchemy
-from sqlalchemy import (
-    MetaData,
-    Table,
-    create_engine,
-    inspect,
-    select,
-    text,
-)
+from sqlalchemy import MetaData, Table, create_engine, inspect, select, text
 from sqlalchemy.engine import Engine
 from sqlalchemy.exc import ProgrammingError, SQLAlchemyError
 from sqlalchemy.schema import CreateTable
@@ -27,6 +20,21 @@ def _format_index(index: sqlalchemy.engine.interfaces.ReflectedIndex) -> str:
     )
 
 
+def truncate_word(content: Any, *, length: int, suffix: str = "...") -> str:
+    """
+    Truncate a string to a certain number of words, based on the max string
+    length.
+    """
+
+    if not isinstance(content, str) or length <= 0:
+        return content
+
+    if len(content) <= length:
+        return content
+
+    return content[: length - len(suffix)].rsplit(" ", 1)[0] + suffix
+
+
 class SQLDatabase:
     """SQLAlchemy wrapper around a database."""
 
@@ -41,6 +49,7 @@ class SQLDatabase:
         indexes_in_table_info: bool = False,
         custom_table_info: Optional[dict] = None,
         view_support: bool = False,
+        max_string_length: int = 300,
     ):
         """Create engine from database URI."""
         self._engine = engine
@@ -95,6 +104,8 @@ class SQLDatabase:
                 if table in intersection
             )
 
+        self._max_string_length = max_string_length
+
         self._metadata = metadata or MetaData()
         # including view support if view_support = true
         self._metadata.reflect(
@@ -322,6 +333,7 @@ class SQLDatabase:
 
         If the statement returns rows, a string of the results is returned.
         If the statement returns no rows, an empty string is returned.
+
         """
         with self._engine.begin() as connection:
             if self._schema is not None:
@@ -338,10 +350,28 @@ class SQLDatabase:
                 if fetch == "all":
                     result = cursor.fetchall()
                 elif fetch == "one":
-                    result = cursor.fetchone()[0]  # type: ignore
+                    result = cursor.fetchone()  # type: ignore
                 else:
                     raise ValueError("Fetch parameter must be either 'one' or 'all'")
-                return str(result)
+
+                # Convert columns values to string to avoid issues with sqlalchmey
+                # trunacating text
+                if isinstance(result, list):
+                    return str(
+                        [
+                            tuple(
+                                truncate_word(c, length=self._max_string_length)
+                                for c in r
+                            )
+                            for r in result
+                        ]
+                    )
+
+                return str(
+                    tuple(
+                        truncate_word(c, length=self._max_string_length) for c in result
+                    )
+                )
         return ""
 
     def get_table_info_no_throw(self, table_names: Optional[List[str]] = None) -> str:

tests/unit_tests/test_sql_database.py

@@ -1,9 +1,18 @@
 # flake8: noqa=E501
 """Test SQL database wrapper."""
 
-from sqlalchemy import Column, Integer, MetaData, String, Table, create_engine, insert
+from sqlalchemy import (
+    Column,
+    Integer,
+    MetaData,
+    String,
+    Table,
+    Text,
+    create_engine,
+    insert,
+)
 
-from langchain.sql_database import SQLDatabase
+from langchain.sql_database import SQLDatabase, truncate_word
 
 metadata_obj = MetaData()
 
@@ -12,6 +21,7 @@ user = Table(
     metadata_obj,
     Column("user_id", Integer, primary_key=True),
     Column("user_name", String(16), nullable=False),
+    Column("user_bio", Text, nullable=True),
 )
 
 company = Table(
@@ -32,11 +42,12 @@ def test_table_info() -> None:
     CREATE TABLE user (
             user_id INTEGER NOT NULL,
             user_name VARCHAR(16) NOT NULL,
+            user_bio TEXT,
             PRIMARY KEY (user_id)
     )
     /*
     3 rows from user table:
-    user_id user_name
+    user_id user_name user_bio
     /*
 
 
@@ -59,8 +70,8 @@ def test_table_info_w_sample_rows() -> None:
     engine = create_engine("sqlite:///:memory:")
     metadata_obj.create_all(engine)
     values = [
-        {"user_id": 13, "user_name": "Harrison"},
-        {"user_id": 14, "user_name": "Chase"},
+        {"user_id": 13, "user_name": "Harrison", "user_bio": "bio"},
+        {"user_id": 14, "user_name": "Chase", "user_bio": "bio"},
     ]
     stmt = insert(user).values(values)
     with engine.begin() as conn:
@@ -84,13 +95,14 @@ def test_table_info_w_sample_rows() -> None:
         CREATE TABLE user (
         user_id INTEGER NOT NULL,
         user_name VARCHAR(16) NOT NULL,
+        user_bio TEXT,
         PRIMARY KEY (user_id)
         )
         /*
         2 rows from user table:
-        user_id user_name
-        13 Harrison
-        14 Chase
+        user_id user_name user_bio
+        13 Harrison bio
+        14 Chase bio
         */
         """
 
@@ -101,13 +113,16 @@ def test_sql_database_run() -> None:
     """Test that commands can be run successfully and returned in correct format."""
     engine = create_engine("sqlite:///:memory:")
     metadata_obj.create_all(engine)
-    stmt = insert(user).values(user_id=13, user_name="Harrison")
+    stmt = insert(user).values(
+        user_id=13, user_name="Harrison", user_bio="That is my Bio " * 24
+    )
     with engine.begin() as conn:
         conn.execute(stmt)
     db = SQLDatabase(engine)
-    command = "select user_name from user where user_id = 13"
+    command = "select user_id, user_name, user_bio from user where user_id = 13"
     output = db.run(command)
-    expected_output = "[('Harrison',)]"
+    user_bio = "That is my Bio " * 19 + "That is my..."
+    expected_output = f"[(13, 'Harrison', '{user_bio}')]"
     assert output == expected_output
 
 
@@ -123,3 +138,11 @@ def test_sql_database_run_update() -> None:
     output = db.run(command)
     expected_output = ""
     assert output == expected_output
+
+
+def test_truncate_word() -> None:
+    assert truncate_word("Hello World", length=5) == "He..."
+    assert truncate_word("Hello World", length=0) == "Hello World"
+    assert truncate_word("Hello World", length=-10) == "Hello World"
+    assert truncate_word("Hello World", length=5, suffix="!!!") == "He!!!"
+    assert truncate_word("Hello World", length=12, suffix="!!!") == "Hello World"