issue #106: improve exception handling in fertiscan

[k-allagbe]

Changes:

• For each of metadata and queries, there now is a module for all the errors.
• The errors now have a hierarchy which helps when handling a group of exceptions at once

Query exceptions hierarchy:

    Exception
    |__QueryError
       |__InspectionQueryError
       |__LabelInformationQueryError
       |__LabelDimensionQueryError
       |__MetricQueryError
       |__UnitQueryError
       |__ElementCompoundQueryError
       |__MicronutrientQueryError
       |__GuaranteedAnalysisQueryError
       |__OrganizationQueryError
       |__OrganizationInformationQueryError
       |__LocationQueryError
       |__RegionQueryError
       |__ProvinceQueryError
       |__SpecificationQueryError
       |__SubLabelQueryError
       |__SubTypeQueryError

Each QueryError sub type exception has specific errors related to creation, retrieval, updating, and deletion, as well as a 'not found' error.

Metadata exceptions hierarchy:

    Exception
    |__MetadataError
       |__BuildInspectionImportError
       |__BuildInspectionExportError
       |__NPKError

• Because the error handling pattern is the same for pretty much all the query functions, we use a decorator to minimize code repetition:

def handle_query_errors(error_cls=QueryError):
    """Decorator for handling query errors."""

    def decorator(func):
        @wraps(func)
        def wrapper(*args, **kwargs):
            try:
                return func(*args, **kwargs)
            except QueryError:
                raise
            except Error as db_error:
                raise error_cls(f"Database error: {db_error}") from db_error
            except Exception as e:
                raise error_cls(f"Unexpected error: {e}") from e

        return wrapper

    return decorator

The code using a decorator:

@handle_query_errors(LabelInformationRetrievalError)
def get_label_information_json(cursor, label_info_id) -> dict:
    query = """
        SELECT get_label_info_json(%s);
        """
    cursor.execute(query, (str(label_info_id),))
    label_info = cursor.fetchone()
    if label_info is None or label_info[0] is None:
        raise LabelInformationNotFoundError(
            "Error: could not get the label information: " + str(label_info_id)
        )
    return label_info[0]

is equivalent to:

def get_label_information_json(cursor, label_info_id) -> dict:
    try:
        query = """
            SELECT get_label_info_json(%s);
            """
        cursor.execute(query, (str(label_info_id),))
        label_info = cursor.fetchone()
        if label_info is None or label_info[0] is None:
            raise LabelInformationNotFoundError(
                "Error: could not get the label information: " + str(label_info_id)
            )
        return label_info[0]
    except QueryError:
        raise
    except Error as db_error:
        raise LabelInformationRetrievalError(f"Database error: {db_error}") from db_error
    except Exception as e:
        raise LabelInformationRetrievalError(f"Unexpected error: {e}") from e

Note that LabelInformationNotFoundError is a QueryError.

[Francois-Werbrouck]

After a fresh review, I think the error file will help maintain the project in the long run!

[k-allagbe]

This issue will not fix #108 as that is core datastore code that might affect nachet.