sqlalchemy.sql.sqltypes.NullType

class documentation

class NullType(TypeEngine):

Known subclasses: sqlalchemy.dialects.postgresql.pg8000._PGNullType

An unknown type.

.NullType is used as a default type for those cases where a type cannot be determined, including:

During table reflection, when the type of a column is not recognized by the .Dialect
When constructing SQL expressions using plain Python objects of unknown types (e.g. somecolumn == my_special_object)
When a new _schema.Column is created, and the given type is passed as None or is not passed at all.

The .NullType can be used within SQL expression invocation without issue, it just has no behavior either at the expression construction level or at the bind-parameter/result processing level. .NullType will result in a .CompileError if the compiler is asked to render the type itself, such as if it is used in a .cast operation or within a schema creation operation such as that invoked by _schema.MetaData.create_all or the .CreateTable construct.

Class	`Comparator`	Undocumented
Method	`literal_processor`	Return a conversion function for processing literal values that are to be rendered directly without using binds.
Class Variable	`__visit_name__`	Undocumented
Class Variable	`_isnull`	Undocumented

Inherited from TypeEngine:

Method	`adapt`	Produce an "adapted" form of this type, given an "impl" class to work with.
Method	`as_generic`	Return an instance of the generic type corresponding to this type using heuristic rule. The method may be overridden if this heuristic rule is not sufficient.
Method	`bind_expression`	Given a bind value (i.e. a `.BindParameter` instance), return a SQL expression in its place.
Method	`bind_processor`	Return a conversion function for processing bind values.
Method	`coerce_compared_value`	Suggest a type for a 'coerced' Python value in an expression.
Method	`column_expression`	Given a SELECT column expression, return a wrapping SQL expression.
Method	`compare_against_backend`	Compare this type against the given backend type.
Method	`compare_values`	Compare two values for equality.
Method	`compile`	Produce a string-compiled form of this `.TypeEngine`.
Method	`dialect_impl`	Return a dialect-specific implementation for this `.TypeEngine`.
Method	`evaluates_none`	Return a copy of this type which has the `.should_evaluate_none` flag set to True.
Method	`get_dbapi_type`	Return the corresponding type object from the underlying DB-API, if any.
Method	`result_processor`	Return a conversion function for processing result row values.
Method	`with_variant`	Produce a new type object that will utilize the given type when applied to the dialect of the given name.
Class Variable	`hashable`	Flag, if False, means values from this type aren't hashable.
Class Variable	`should_evaluate_none`	If True, the Python constant `None` is considered to be handled explicitly by this type.
Class Variable	`sort_key_function`	A sorting function that can be passed as the key to sorted.
Static Method	`_to_instance`	Undocumented
Method	`__repr__`	Undocumented
Method	`__str__`	Undocumented
Method	`_cached_bind_processor`	Return a dialect-specific bind processor for this type.
Method	`_cached_custom_processor`	Undocumented
Method	`_cached_literal_processor`	Return a dialect-specific literal processor for this type.
Method	`_cached_result_processor`	Return a dialect-specific result processor for this type.
Method	`_compare_type_affinity`	Undocumented
Method	`_default_dialect`	Undocumented
Method	`_dialect_info`	Return a dialect-specific registry which caches a dialect-specific implementation, bind processing function, and one or more result processing functions.
Method	`_gen_dialect_impl`	Undocumented
Method	`_resolve_for_literal`	adjust this type given a literal Python value that will be stored in a bound parameter.
Method	`_unwrapped_dialect_impl`	Return the 'unwrapped' dialect impl for this type.
Method	`copy`	Undocumented
Method	`copy_value`	Undocumented
Class Variable	`_is_array`	Undocumented
Class Variable	`_is_table_value`	Undocumented
Class Variable	`_is_tuple_type`	Undocumented
Class Variable	`_is_type_decorator`	Undocumented
Class Variable	`_sqla_type`	Undocumented
Property	`_generic_type_affinity`	Undocumented
Property	`_has_bind_expression`	memoized boolean, check if bind_expression is implemented.
Property	`_has_column_expression`	memoized boolean, check if column_expression is implemented.
Property	`_static_cache_key`	Undocumented
Property	`_type_affinity`	Return a rudimental 'affinity' value expressing the general class of type.
Property	`python_type`	Return the Python type object expected to be returned by instances of this type, if known.

Inherited from Traversible (via TypeEngine):

Method	`get_children`	Return immediate child `.visitors.Traversible` elements of this `.visitors.Traversible`.
Method	`__class_getitem__`	Undocumented

def literal_processor(self, dialect):

overrides sqlalchemy.types.TypeEngine.literal_processor

Return a conversion function for processing literal values that are to be rendered directly without using binds.

This function is used when the compiler makes use of the "literal_binds" flag, typically used in DDL generation as well as in certain scenarios where backends don't accept bound parameters.

Returns a callable which will receive a literal Python value as the sole positional argument and will return a string representation to be rendered in a SQL statement.

Note

This method is only called relative to a dialect specific type object, which is often private to a dialect in use and is not the same type object as the public facing one, which means it's not feasible to subclass a .types.TypeEngine class in order to provide an alternate _types.TypeEngine.literal_processor method, unless subclassing the _types.UserDefinedType class explicitly.

To provide alternate behavior for _types.TypeEngine.literal_processor, implement a _types.TypeDecorator class and provide an implementation of _types.TypeDecorator.process_literal_param.