[langchain-db2] Changed behavior when searching for an empty table after updating `ibm-db` to version 3.2.7.

[Mateusz-Switala]

After updating ibm-db to version 3.2.7, the behavior of DB2VS.similarity_search changed from returning an empty list to raising an error.

Examples

ibm-db==3.2.7

from langchain_db2 import DB2VS

db2_vs = DB2VS(
    table_name='empty_table',
    connection_args=db2_connection_args,
    embedding_function=embedding_func
    )

db2_vs.similarity_search("text")

# Output

2025-09-08 11:03:25,144 - ERROR - An unexpected error occurred: 'NoneType' object is not iterable
Traceback (most recent call last):
  File "/Users/.../lib/python3.11/site-packages/langchain_db2/db2vs.py", line 57, in wrapper
    return func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^
  File "/Users/.../lib/python3.11/site-packages/langchain_db2/db2vs.py", line 480, in similarity_search_by_vector_with_relevance_scores
    for result in results:
TypeError: 'NoneType' object is not iterable

ibm-db==3.2.6

from langchain_db2 import DB2VS

db2_vs = DB2VS(
    table_name='empty_table',
    connection_args=db2_connection_args,
    embedding_function=embedding_func
    )

db2_vs.similarity_search("text")

# []

@yiweiHeOSS Could you take a look at this?

[yiweiHeOSS]

It looks like the ibm-db package team modified their code the and the code like results = cursor.fetchall() will return NoneType, which is not iterable through for result in results:

[yiweiHeOSS]

@bimalkjha

[yiweiHeOSS]

Hi @bimalkjha, do you know if your team changed the behavior of results = cursor.fetchall() recently and return NoneType? Thanks.

[bimalkjha]

@yiweiHeOSS Yes, cursor.fetchall() behavior changed in 3.2.7. The None type is getting returned from this line: https://github.com/ibmdb/python-ibmdb/blob/master/ibm_db.c#L17381
But, this code was existing in v3.2.6 too. I would suggest to open an issue in ibm_db with repro to get clarity. Thanks.

[bimalkjha]

It seems it is caused by the code change in ibmdb/python-ibmdb@eec53c1 for ibm_db_dbi.py. I would talk to the developer who did this change and then comment for clarity. He is on leave today. Thanks.

[bimalkjha]

@yiweiHeOSS @Mateusz-Switala We'll update ibm_db code to return empty list for cursor.fetchall() and ibm_db.fetchall(). Currently, both APIs are returning None if query return empty result.
Meanwhile, you may update db2vs.py code to have check for None and then proceed. Thanks.

[Mateusz-Switala]

@bimalkjha Do you have any ETA for that fix?

[bimalkjha]

@Mateusz-Switala Fix of this issue is already delivered to ibm_db on github and it will be available with next release of ibm_db. To test the fix, you can install ibm_db using pip install https://github.com/ibmdb/python-ibmdb/archive/refs/heads/master.zip command and verify. Thanks.