SQLModel `session.get()` Fails: Resolving NoSuchColumnError

Nov 17, 2025 by Alex Johnson 60 views

SQLModel `session.get()` Fails with `NoSuchColumnError`: A Comprehensive Guide

Encountering errors while working with databases can be frustrating. One common issue in SQLModel, especially when integrated with database systems like DynamoDB through libraries like pydynamodb, is the NoSuchColumnError when using the session.get() method. This article delves into the causes, solutions, and best practices for troubleshooting this error. We'll explore the error in detail, provide a reproducible example, and offer step-by-step guidance to resolve it effectively.

Understanding the `NoSuchColumnError` in SQLModel

When using SQLModel, the NoSuchColumnError typically arises when the system fails to locate a specified column during a database operation. In the context of session.get(), this usually means that SQLAlchemy, the underlying ORM (Object-Relational Mapper) that SQLModel leverages, cannot find the column referenced in your model within the database table. Understanding this error is crucial for efficiently debugging and resolving issues in your database interactions.

The error message, sqlalchemy.exc.NoSuchColumnError: Could not locate column in row for column 'team.id', clearly indicates that the system is unable to find the id column within the team table. This can occur due to several reasons, such as discrepancies between the model definition and the actual database schema, incorrect table or column names, or issues with the database connection and configuration. To effectively troubleshoot this, it's essential to examine your model definitions, database schema, and connection settings to identify the root cause of the problem.

This error can be particularly perplexing when working with NoSQL databases like DynamoDB, which have different schema management approaches compared to traditional relational databases. In DynamoDB, the schema is more flexible, and column definitions are not as strict as in SQL databases. Therefore, ensuring that your SQLModel definitions align with how DynamoDB structures and handles data is crucial. This involves verifying that the primary key and other indexed attributes are correctly defined in your model and that the database table is set up to match these definitions. By carefully aligning your SQLModel models with your DynamoDB table structure, you can avoid the NoSuchColumnError and ensure smooth data retrieval and manipulation.

Minimal Reproducible Example

To illustrate the issue, consider the following minimal reproducible example. This code snippet demonstrates how the NoSuchColumnError can occur when using session.get() with SQLModel and pydynamodb.

import uuid
from pydynamodb import sqlalchemy_dynamodb
from sqlalchemy.engine import create_engine
from sqlmodel import Session, Field, SQLModel
import boto3


class Team(SQLModel, table=True):
    id: str = Field(default_factory=lambda: uuid.uuid4().hex, primary_key=True)
    name: str = Field(index=True)
    headquarters: str


session = boto3.Session()
client = session.client("dynamodb")
credentials = session.get_credentials()
aws_access_key_id = credentials.access_key
aws_secret_access_key = credentials.secret_key
region_name = session.region_name

conn_str = (
    "dynamodb://{aws_access_key_id}:{aws_secret_access_key}@dynamodb.{region_name}.amazonaws.com:443"
).format(
    aws_access_key_id=aws_access_key_id,
    aws_secret_access_key=aws_secret_access_key,
    region_name=region_name,
)
engine = create_engine(conn_str, echo=True)

with Session(engine) as session:
    results = session.get(Team, "some-id")
    print(results)

This code defines a Team model with fields id, name, and headquarters. It then sets up a connection to DynamoDB using pydynamodb and attempts to retrieve a Team instance by its ID using session.get(). When executed, this code results in the NoSuchColumnError, demonstrating the problem we are addressing. The traceback highlights the failure in the SQLAlchemy engine when trying to map the database results to the model, specifically when accessing the id column.

By providing this example, you can directly observe the error and test potential solutions in your environment. This hands-on approach is invaluable for understanding the nuances of the issue and ensuring that the fixes you implement are effective. You can modify and experiment with this code snippet to better grasp the underlying mechanisms and verify your understanding of how SQLModel interacts with DynamoDB. This proactive troubleshooting method will ultimately lead to more robust and reliable database interactions in your applications.

Observed Behavior and Error Traceback

When running the above code, the following error traceback is observed:

2025-11-17 18:59:27,674 INFO sqlalchemy.engine.Engine BEGIN (implicit)
2025-11-17 18:59:27,675 INFO sqlalchemy.engine.Engine SELECT id, name, headquarters 
FROM team 
WHERE id = ?
2025-11-17 18:59:27,675 INFO sqlalchemy.engine.Engine [generated in 0.00011s] ('some-id',)
2025-11-17 18:59:28,050 INFO sqlalchemy.engine.Engine ROLLBACK
Traceback (most recent call last):
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/cursor.py", line 859, in _indexes_for_keys
    return [self._keymap[key][0] for key in keys]
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/cursor.py", line 859, in <listcomp>
    return [self._keymap[key][0] for key in keys]
            ~~~~~~~~~~~~^^^^^
KeyError: Column('id', AutoString(), table=<team>, primary_key=True, nullable=False, default=CallableColumnDefault(<function Team.<lambda> at 0x77df6c97a160>))

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/tmp/test/main.py", line 33, in <module>
    results = session.get(Team, "some-id")
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 3680, in get
    return self._get_impl(
           ^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 3859, in _get_impl
    return db_load_fn(
           ^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/loading.py", line 695, in load_on_pk_identity
    session.execute(
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlmodel/orm/session.py", line 144, in execute
    return super().execute(
           ^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 2351, in execute
    return self._execute_internal(
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/session.py", line 2249, in _execute_internal
    result: Result[Any] = compile_state_cls.orm_execute_statement(
                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/context.py", line 309, in orm_execute_statement
    return cls.orm_setup_cursor_result(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/context.py", line 616, in orm_setup_cursor_result
    return loading.instances(result, querycontext)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/loading.py", line 133, in instances
    with util.safe_reraise():
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/util/langhelpers.py", line 224, in __exit__
    raise exc_value.with_traceback(exc_tb)
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/loading.py", line 114, in instances
    *[
     ^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/loading.py", line 115, in <listcomp>
    query_entity.row_processor(context, cursor)
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/context.py", line 2786, in row_processor
    _instance = loading._instance_processor(
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/orm/loading.py", line 878, in _instance_processor
    primary_key_getter = result._tuple_getter(pk_cols)
                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/result.py", line 1189, in _tuple_getter
    return self._metadata._row_as_tuple_getter(keys)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/result.py", line 179, in _row_as_tuple_getter
    indexes = self._indexes_for_keys(keys)
              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/cursor.py", line 862, in _indexes_for_keys
    CursorResultMetaData._key_fallback(self, ke.args[0], ke)
  File "/home/user/miniconda3/envs/test/lib/python3.11/site-packages/sqlalchemy/engine/cursor.py", line 825, in _key_fallback
    raise exc.NoSuchColumnError(
sqlalchemy.exc.NoSuchColumnError: Could not locate column in row for column 'team.id'

The traceback indicates that the error occurs within SQLAlchemy's engine, specifically in the cursor processing logic. The KeyError and subsequent NoSuchColumnError highlight that the system cannot find the id column when mapping the database row to the Team model. This detailed error traceback is invaluable for pinpointing the exact location and nature of the problem, allowing for more targeted and effective troubleshooting efforts.

Analyzing the traceback, you can trace the error back to the interaction between SQLAlchemy and the database driver (pydynamodb in this case). The engine attempts to retrieve column information but fails, leading to the exception. This type of error often suggests a mismatch between the expected schema (defined in the SQLModel model) and the actual schema or data structure in the database. Understanding this interaction is crucial for developing strategies to resolve the NoSuchColumnError and ensuring your applications function correctly.

Potential Causes and Solutions

Several factors can contribute to the NoSuchColumnError when using SQLModel with DynamoDB via pydynamodb. Here are some common causes and their corresponding solutions:

1. Mismatched Column Definitions

One of the most frequent causes is a discrepancy between the column definitions in your SQLModel model and the actual attributes in your DynamoDB table. This can occur if the model's field names do not exactly match the attribute names in DynamoDB, or if there are differences in data types. To resolve this, ensure that your SQLModel field names and types align precisely with the attributes defined in your DynamoDB table. Pay close attention to case sensitivity and spelling, as even minor differences can lead to errors.

For example, if your DynamoDB table has an attribute named team_id while your SQLModel model defines a field named id, the NoSuchColumnError will occur. Similarly, if an attribute is stored as a string in DynamoDB but defined as an integer in your model, SQLAlchemy will be unable to map the data correctly. Review your model definitions and compare them to your DynamoDB schema to identify and correct any mismatches.

2. Missing Primary Key Configuration

Another common issue is the incorrect or missing configuration of primary keys in your SQLModel model. DynamoDB requires a primary key (either a partition key or a composite key consisting of a partition key and a sort key) for efficient data retrieval. If the primary key is not correctly defined in your SQLModel model, SQLAlchemy may generate incorrect queries, leading to the NoSuchColumnError. Ensure that the primary key field in your SQLModel model is properly annotated with primary_key=True in the Field definition.

In the example code, the id field is defined as the primary key using id: str = Field(default_factory=lambda: uuid.uuid4().hex, primary_key=True). If this annotation were missing or incorrect, the error would likely occur. Verify that all primary key fields in your model are correctly marked and that they correspond to the primary key attributes defined in your DynamoDB table. Proper primary key configuration is essential for both performance and correctness when working with DynamoDB and SQLModel.

3. Incompatible Data Types

Data type mismatches between your SQLModel model and DynamoDB attributes can also trigger the NoSuchColumnError. DynamoDB supports a variety of data types, including strings, numbers, booleans, lists, and maps. If the data type defined in your SQLModel model does not match the type of the corresponding attribute in DynamoDB, SQLAlchemy will be unable to read the data correctly. For example, if you define a field as an integer in SQLModel but the attribute is stored as a string in DynamoDB, you will encounter this error.

To resolve data type mismatches, carefully review your model definitions and compare them to the data types of the attributes in your DynamoDB table. Ensure that you are using compatible types in your SQLModel model. For instance, if an attribute is a number in DynamoDB, the corresponding field in SQLModel should be defined as int or float. Consistent data type definitions are crucial for seamless data mapping and retrieval, preventing the NoSuchColumnError and ensuring data integrity.

4. Issues with `pydynamodb`

As pydynamodb serves as the SQLAlchemy dialect for DynamoDB, issues within this library can also lead to errors. If pydynamodb does not correctly translate SQLModel queries into DynamoDB operations, or if it fails to handle the response from DynamoDB properly, you may encounter the NoSuchColumnError. Ensure that you are using a compatible version of pydynamodb with your SQLModel and SQLAlchemy versions. Check the pydynamodb documentation and release notes for any known issues or compatibility requirements.

Additionally, consider upgrading to the latest version of pydynamodb if you are using an older version, as newer releases often include bug fixes and performance improvements. If the issue persists, you may need to delve deeper into pydynamodb's implementation or consult its community for specific guidance. Verifying that pydynamodb is correctly configured and functioning as expected is an essential step in troubleshooting database-related errors when working with DynamoDB and SQLModel.

5. Table Naming Conventions and Case Sensitivity

DynamoDB is case-sensitive, so table names and attribute names must match exactly between your SQLModel model and your DynamoDB table. If there is a case mismatch, such as defining a table as Team in SQLModel but having it named teams in DynamoDB, the system will not be able to find the correct table or columns. Always double-check that your table names and attribute names are consistent in terms of case and spelling.

In SQLModel, you define the table name using the table=True option in the model and the __tablename__ attribute if needed. Ensure that the name you provide here matches the exact name of your DynamoDB table. Similarly, verify that the attribute names in your SQLModel fields match the attribute names in your DynamoDB items. Case sensitivity is a common pitfall that can lead to the NoSuchColumnError, so meticulous attention to naming conventions is essential for avoiding this issue.

Step-by-Step Guide to Resolving `NoSuchColumnError`

To effectively resolve the NoSuchColumnError, follow these steps:

Inspect the Error Traceback: Carefully examine the full traceback to understand the exact point of failure. Identify which column is causing the issue and the specific SQLModel operation that triggered the error. The traceback provides valuable context for diagnosing the problem.
Verify Model Definitions: Review your SQLModel model definitions, paying close attention to field names, data types, and primary key configurations. Ensure that these definitions accurately reflect the structure and attributes of your DynamoDB table. Use the reproducible example provided earlier to test and validate your model definitions.
Check DynamoDB Schema: Use the AWS Management Console or AWS CLI to inspect your DynamoDB table schema. Verify that the table exists, that the column names match your model definitions, and that the data types are compatible. Ensure that the primary key is correctly defined in your DynamoDB table.
Ensure Consistent Naming: Double-check that table names and attribute names are consistent between your SQLModel models and your DynamoDB tables. Pay special attention to case sensitivity, as DynamoDB is case-sensitive. Any discrepancies in naming can lead to the NoSuchColumnError.
Update pydynamodb: Ensure you are using a compatible and up-to-date version of pydynamodb. Check the library's documentation and release notes for any known issues or compatibility requirements. Consider upgrading to the latest version to benefit from bug fixes and performance improvements.
Test with Simple Queries: Try running simple queries directly against your DynamoDB table using the AWS CLI or boto3 to verify that the table and data are accessible. This can help isolate whether the issue is with SQLModel and pydynamodb or with the underlying DynamoDB setup.
Review Connection Configuration: Verify that your database connection string is correctly configured. Ensure that your AWS credentials (access key ID, secret access key, and region) are properly set and that your application has the necessary permissions to access DynamoDB. Incorrect connection settings can prevent SQLModel from accessing the table schema.

Expected Behavior After Resolution

After resolving the NoSuchColumnError, the session.get() method should function as expected, returning an instance of your model if a matching record is found in the database, or None if no record matches the given primary key. The application should no longer throw the NoSuchColumnError or any related exceptions during database operations.

For example, with the corrected model and connection configuration, the code snippet `results = session.get(Team,