SQLAlchemy ORM exceptions.
An attempt to access unloaded attributes on a mapped instance that is detached.
A invalid condition was detected during flush().
A single database result was required but more than one were found.
Exception types that may be raised by instrumentation implementations.
A database result was required but none was found.
A refresh operation failed to retrieve the database row corresponding to an object’s known primary key identity.
A refresh operation proceeds when an expired attribute is accessed on an object, or when Query.get() is used to retrieve an object which is, upon retrieval, detected as expired. A SELECT is emitted for the target row based on primary key; if no row is returned, this exception is raised.
The true meaning of this exception is simply that no row exists for the primary key identifier associated with a persistent object. The row may have been deleted, or in some cases the primary key updated to a new value, outside of the ORM’s management of the target object.
An operation encountered database state that is unaccounted for.
Two conditions cause this to happen:
An mapping operation was requested for an unknown class.
Mapping operation was requested on an unknown column.
Base for exceptions that involve expected mappings not present.