SQLAlchemy provides abstractions for most common database data types, and a mechanism for specifying your own custom data types.
The methods and attributes of type objects are rarely used directly. Type objects are supplied to Table definitions and can be supplied as type hints to functions for occasions where the database driver returns an incorrect type.
>>> users = Table('users', metadata,
... Column('id', Integer, primary_key=True)
... Column('login', String(32))
... )
SQLAlchemy will use the Integer and String(32) type information when issuing a CREATE TABLE statement and will use it again when reading back rows SELECTed from the database. Functions that accept a type (such as Column()) will typically accept a type class or instance; Integer is equivalent to Integer() with no construction arguments in this case.
Generic types specify a column that can read, write and store a particular type of Python data. SQLAlchemy will choose the best database column type available on the target database when issuing a CREATE TABLE statement. For complete control over which column type is emitted in CREATE TABLE, such as VARCHAR see SQL Standard Types and the other sections of this chapter.
Bases: sqlalchemy.types.Integer
A type for bigger int integers.
Typically generates a BIGINT in DDL, and otherwise acts like a normal Integer on the Python side.
Bases: sqlalchemy.types.TypeEngine, sqlalchemy.types.SchemaType
A bool datatype.
Boolean typically uses BOOLEAN or SMALLINT on the DDL side, and on the Python side deals in True or False.
Construct a Boolean.
Parameters: |
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Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeEngine
A type for datetime.date() objects.
Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeEngine
A type for datetime.datetime() objects.
Date and time types return objects from the Python datetime module. Most DBAPIs have built in support for the datetime module, with the noted exception of SQLite. In the case of SQLite, date and time types are stored as strings which are then converted back to datetime objects when rows are returned.
Bases: sqlalchemy.types.String, sqlalchemy.types.SchemaType
Generic Enum Type.
The Enum type provides a set of possible string values which the column is constrained towards.
By default, uses the backend’s native ENUM type if available, else uses VARCHAR + a CHECK constraint.
See also
ENUM - PostgreSQL-specific type, which has additional functionality.
Construct an enum.
Keyword arguments which don’t apply to a specific backend are ignored by that backend.
Parameters: |
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Issue CREATE ddl for this type, if applicable.
Issue DROP ddl for this type, if applicable.
Bases: sqlalchemy.types.Numeric
Type representing floating point types, such as FLOAT or REAL.
This type returns Python float objects by default, unless the Float.asdecimal flag is set to True, in which case they are coerced to decimal.Decimal objects.
Note
The Float type is designed to receive data from a database type that is explicitly known to be a floating point type (e.g. FLOAT, REAL, others) and not a decimal type (e.g. DECIMAL, NUMERIC, others). If the database column on the server is in fact a Numeric type, such as DECIMAL or NUMERIC, use the Numeric type or a subclass, otherwise numeric coercion between float/Decimal may or may not function as expected.
Construct a Float.
Parameters: |
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Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeEngine
A type for int integers.
Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeDecorator
A type for datetime.timedelta() objects.
The Interval type deals with datetime.timedelta objects. In PostgreSQL, the native INTERVAL type is used; for others, the value is stored as a date which is relative to the “epoch” (Jan. 1, 1970).
Note that the Interval type does not currently provide date arithmetic operations on platforms which do not support interval types natively. Such operations usually require transformation of both sides of the expression (such as, conversion of both sides into integer epoch values first) which currently is a manual procedure (such as via func).
Construct an Interval object.
Parameters: |
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See TypeEngine.coerce_compared_value() for a description.
Bases: sqlalchemy.types._Binary
A type for large binary byte data.
The Binary type generates BLOB or BYTEA when tables are created, and also converts incoming values using the Binary callable provided by each DB-API.
Construct a LargeBinary type.
Parameters: | length¶ – optional, a length for the column for use in DDL statements, for those BLOB types that accept a length (i.e. MySQL). It does not produce a small BINARY/VARBINARY type - use the BINARY/VARBINARY types specifically for those. May be safely omitted if no CREATE TABLE will be issued. Certain databases may require a length for use in DDL, and will raise an exception when the CREATE TABLE DDL is issued. |
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Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeEngine
A type for fixed precision numbers, such as NUMERIC or DECIMAL.
This type returns Python decimal.Decimal objects by default, unless the Numeric.asdecimal flag is set to False, in which case they are coerced to Python float objects.
Note
The Numeric type is designed to receive data from a database type that is explicitly known to be a decimal type (e.g. DECIMAL, NUMERIC, others) and not a floating point type (e.g. FLOAT, REAL, others). If the database column on the server is in fact a floating-point type type, such as FLOAT or REAL, use the Float type or a subclass, otherwise numeric coercion between float/Decimal may or may not function as expected.
Note
The Python decimal.Decimal class is generally slow performing; cPython 3.3 has now switched to use the cdecimal library natively. For older Python versions, the cdecimal library can be patched into any application where it will replace the decimal library fully, however this needs to be applied globally and before any other modules have been imported, as follows:
import sys
import cdecimal
sys.modules["decimal"] = cdecimal
Note that the cdecimal and decimal libraries are not compatible with each other, so patching cdecimal at the global level is the only way it can be used effectively with various DBAPIs that hardcode to import the decimal library.
Construct a Numeric.
Parameters: |
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When using the Numeric type, care should be taken to ensure that the asdecimal setting is apppropriate for the DBAPI in use - when Numeric applies a conversion from Decimal->float or float-> Decimal, this conversion incurs an additional performance overhead for all result columns received.
DBAPIs that return Decimal natively (e.g. psycopg2) will have better accuracy and higher performance with a setting of True, as the native translation to Decimal reduces the amount of floating- point issues at play, and the Numeric type itself doesn’t need to apply any further conversions. However, another DBAPI which returns floats natively will incur an additional conversion overhead, and is still subject to floating point data loss - in which case asdecimal=False will at least remove the extra conversion overhead.
Bases: sqlalchemy.types.TypeDecorator
Holds Python objects, which are serialized using pickle.
PickleType builds upon the Binary type to apply Python’s pickle.dumps() to incoming objects, and pickle.loads() on the way out, allowing any pickleable Python object to be stored as a serialized binary field.
To allow ORM change events to propagate for elements associated with PickleType, see Mutation Tracking.
Construct a PickleType.
Parameters: |
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alias of LargeBinary
Bases: sqlalchemy.sql.expression.SchemaEventTarget
Mark a type as possibly requiring schema-level DDL for usage.
Supports types that must be explicitly created/dropped (i.e. PG ENUM type) as well as types that are complimented by table or schema level constraints, triggers, and other rules.
SchemaType classes can also be targets for the DDLEvents.before_parent_attach() and DDLEvents.after_parent_attach() events, where the events fire off surrounding the association of the type object with a parent Column.
Issue CREATE ddl for this type, if applicable.
Issue DROP ddl for this type, if applicable.
Bases: sqlalchemy.types.Integer
A type for smaller int integers.
Typically generates a SMALLINT in DDL, and otherwise acts like a normal Integer on the Python side.
Bases: sqlalchemy.types.Concatenable, sqlalchemy.types.TypeEngine
The base for all string and character types.
In SQL, corresponds to VARCHAR. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.)
The length field is usually required when the String type is used within a CREATE TABLE statement, as VARCHAR requires a length on most databases.
Create a string-holding type.
Parameters: |
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Bases: sqlalchemy.types.String
A variably sized string type.
In SQL, usually corresponds to CLOB or TEXT. Can also take Python unicode objects and encode to the database’s encoding in bind params (and the reverse for result sets.) In general, TEXT objects do not have a length; while some databases will accept a length argument here, it will be rejected by others.
Bases: sqlalchemy.types._DateAffinity, sqlalchemy.types.TypeEngine
A type for datetime.time() objects.
Bases: sqlalchemy.types.String
A variable length Unicode string type.
The Unicode type is a String subclass that assumes input and output as Python unicode data, and in that regard is equivalent to the usage of the convert_unicode flag with the String type. However, unlike plain String, it also implies an underlying column type that is explicitly supporting of non-ASCII data, such as NVARCHAR on Oracle and SQL Server. This can impact the output of CREATE TABLE statements and CAST functions at the dialect level, and can also affect the handling of bound parameters in some specific DBAPI scenarios.
The encoding used by the Unicode type is usually determined by the DBAPI itself; most modern DBAPIs feature support for Python unicode objects as bound values and result set values, and the encoding should be configured as detailed in the notes for the target DBAPI in the Dialects section.
For those DBAPIs which do not support, or are not configured to accommodate Python unicode objects directly, SQLAlchemy does the encoding and decoding outside of the DBAPI. The encoding in this scenario is determined by the encoding flag passed to create_engine().
When using the Unicode type, it is only appropriate to pass Python unicode objects, and not plain str. If a plain str is passed under Python 2, a warning is emitted. If you notice your application emitting these warnings but you’re not sure of the source of them, the Python warnings filter, documented at http://docs.python.org/library/warnings.html, can be used to turn these warnings into exceptions which will illustrate a stack trace:
import warnings
warnings.simplefilter('error')
For an application that wishes to pass plain bytestrings and Python unicode objects to the Unicode type equally, the bytestrings must first be decoded into unicode. The recipe at Coercing Encoded Strings to Unicode illustrates how this is done.
See also:
UnicodeText - unlengthed textual counterpart to Unicode.
Bases: sqlalchemy.types.Text
An unbounded-length Unicode string type.
See Unicode for details on the unicode behavior of this object.
Like Unicode, usage the UnicodeText type implies a unicode-capable type being used on the backend, such as NCLOB, NTEXT.
The SQL standard types always create database column types of the same name when CREATE TABLE is issued. Some types may not be supported on all databases.
Bases: sqlalchemy.types.BigInteger
The SQL BIGINT type.
Bases: sqlalchemy.types._Binary
The SQL BINARY type.
Bases: sqlalchemy.types.LargeBinary
The SQL BLOB type.
Bases: sqlalchemy.types.Boolean
The SQL BOOLEAN type.
Bases: sqlalchemy.types.String
The SQL CHAR type.
Bases: sqlalchemy.types.Text
The CLOB type.
This type is found in Oracle and Informix.
Bases: sqlalchemy.types.Date
The SQL DATE type.
Bases: sqlalchemy.types.DateTime
The SQL DATETIME type.
Bases: sqlalchemy.types.Numeric
The SQL DECIMAL type.
Bases: sqlalchemy.types.Float
The SQL FLOAT type.
Bases: sqlalchemy.types.Integer
The SQL INT or INTEGER type.
Bases: sqlalchemy.types.Unicode
The SQL NCHAR type.
Bases: sqlalchemy.types.Unicode
The SQL NVARCHAR type.
Bases: sqlalchemy.types.Numeric
The SQL NUMERIC type.
Bases: sqlalchemy.types.Float
The SQL REAL type.
Bases: sqlalchemy.types.SmallInteger
The SQL SMALLINT type.
Bases: sqlalchemy.types.Text
The SQL TEXT type.
Bases: sqlalchemy.types.Time
The SQL TIME type.
Bases: sqlalchemy.types.DateTime
The SQL TIMESTAMP type.
Bases: sqlalchemy.types._Binary
The SQL VARBINARY type.
Bases: sqlalchemy.types.String
The SQL VARCHAR type.
Database-specific types are also available for import from each database’s dialect module. See the Dialects reference for the database you’re interested in.
For example, MySQL has a BIGINT type and PostgreSQL has an INET type. To use these, import them from the module explicitly:
from sqlalchemy.dialects import mysql
table = Table('foo', metadata,
Column('id', mysql.BIGINT),
Column('enumerates', mysql.ENUM('a', 'b', 'c'))
)
Or some PostgreSQL types:
from sqlalchemy.dialects import postgresql
table = Table('foo', metadata,
Column('ipaddress', postgresql.INET),
Column('elements', postgresql.ARRAY(String))
)
Each dialect provides the full set of typenames supported by that backend within its __all__ collection, so that a simple import * or similar will import all supported types as implemented for that backend:
from sqlalchemy.dialects.postgresql import *
t = Table('mytable', metadata,
Column('id', INTEGER, primary_key=True),
Column('name', VARCHAR(300)),
Column('inetaddr', INET)
)
Where above, the INTEGER and VARCHAR types are ultimately from sqlalchemy.types, and INET is specific to the Postgresql dialect.
Some dialect level types have the same name as the SQL standard type, but also provide additional arguments. For example, MySQL implements the full range of character and string types including additional arguments such as collation and charset:
from sqlalchemy.dialects.mysql import VARCHAR, TEXT
table = Table('foo', meta,
Column('col1', VARCHAR(200, collation='binary')),
Column('col2', TEXT(charset='latin1'))
)