# SQLAlchemy 0.4 Documentation

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Version: 0.4.1 Last Updated: 11/18/07 17:50:18

### module sqlalchemy.schema

The schema module provides the building blocks for database metadata.

This means all the entities within a SQL database that we might want to look at, modify, or create and delete are described by these objects, in a database-agnostic way.

A structure of SchemaItems also provides a visitor interface which is the primary method by which other methods operate upon the schema. The SQL package extends this structure with its own clause-specific objects as well as the visitor interface, so that the schema package plugs in to the SQL package.

### class CheckConstraint(Constraint)

def __init__(self, sqltext, name=None)

Construct a new `CheckConstraint`.

def copy(self)
__visit_name__ = property()
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### class Column(SchemaItem,_ColumnClause)

Represent a column in a database table.

This is a subclass of `expression.ColumnClause` and represents an actual existing table in the database, in a similar fashion as `TableClause`/`Table`.

def __init__(self, name, type_, *args, **kwargs)

Construct a new `Column` object.

Arguments are:

name
  The name of this column. This should be the identical name as it appears, or will appear, in the database.
type_
  The `TypeEngine` for this column. This can be any subclass of `types.AbstractType`, including the database-agnostic types defined in the types module, database-specific types defined within specific database modules, or user-defined types. If the column contains a ForeignKey, the type can also be None, in which case the type assigned will be that of the referenced column.
*args
  Constraint, ForeignKey, ColumnDefault and Sequence objects should be added as list values.
**kwargs

  Keyword arguments include:

  key
    Defaults to None: an optional alias name for this column. The column will then be identified everywhere in an application, including the column list on its Table, by this key, and not the given name. Generated SQL, however, will still reference the column by its actual name.
  primary_key
    Defaults to False: True if this column is a primary key column. Multiple columns can have this flag set to specify composite primary keys. As an alternative, the primary key of a Table can be specified via an explicit `PrimaryKeyConstraint` instance appended to the Table's list of objects.
  nullable
    Defaults to True : True if this column should allow nulls. True is the default unless this column is a primary key column.
  default
    Defaults to None: a scalar, Python callable, or `ClauseElement` representing the default value for this column, which will be invoked upon insert if this column is not present in the insert list or is given a value of None. The default expression will be converted into a `ColumnDefault` object upon initialization.
  _is_oid
    Defaults to False: used internally to indicate that this column is used as the quasi-hidden "oid" column
  index
    Defaults to False: indicates that this column is indexed. The name of the index is autogenerated. to specify indexes with explicit names or indexes that contain multiple columns, use the `Index` construct instead.
  info
    Defaults to {}: A space to store application specific data; this must be a dictionary.
  unique
    Defaults to False: indicates that this column contains a unique constraint, or if index is True as well, indicates that the Index should be created with the unique flag. To specify multiple columns in the constraint/index or to specify an explicit name, use the `UniqueConstraint` or `Index` constructs instead.
  autoincrement
    Defaults to True: indicates that integer-based primary key columns should have autoincrementing behavior, if supported by the underlying database. This will affect `CREATE TABLE` statements such that they will use the databases auto-incrementing keyword (such as `SERIAL` for Postgres, `AUTO_INCREMENT` for Mysql) and will also affect the behavior of some dialects during `INSERT` statement execution such that they will assume primary key values are created in this manner. If a `Column` has an explicit `ColumnDefault` object (such as via the default keyword, or a `Sequence` or `PassiveDefault`), then the value of autoincrement is ignored and is assumed to be False. autoincrement value is only significant for a column with a type or subtype of Integer.
  quote
    Defaults to False: indicates that the Column identifier must be properly escaped and quoted before being sent to the database. This flag should normally not be required as dialects can auto-detect conditions where quoting is required.

def append_foreign_key(self, fk)
columns = property()
def copy(self)

Create a copy of this `Column`, unitialized.

This is used in `Table.tometadata`.

def get_children(self, schema_visitor=False, **kwargs)
def references(self, column)

return true if this column references the given column via foreign key

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### class ColumnDefault(DefaultGenerator)

A plain default value on a column.

This could correspond to a constant, a callable function, or a SQL clause.

def __init__(self, arg, **kwargs)

Construct a new `ColumnDefault`.

__visit_name__ = property()
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### class Constraint(SchemaItem)

Represent a table-level `Constraint` such as a composite primary key, foreign key, or unique constraint.

Implements a hybrid of dict/setlike behavior with regards to the list of underying columns.

def __init__(self, name=None)

Construct a new `Constraint`.

def copy(self)
def keys(self)
def __add__(self, other)
def __contains__(self, x)
def __iter__(self)
def __len__(self)
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### class DefaultGenerator(SchemaItem)

Base class for column default values.

def __init__(self, for_update=False, metadata=None)

Construct a new `DefaultGenerator`.

def execute(self, bind=None, **kwargs)
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### class ForeignKey(SchemaItem)

Defines a column-level `ForeignKey` constraint between two columns.

`ForeignKey` is specified as an argument to a Column object.

One or more `ForeignKey` objects are used within a `ForeignKeyConstraint` object which represents the table-level constraint definition.

def __init__(self, column, constraint=None, use_alter=False, name=None, onupdate=None, ondelete=None)

Construct a new `ForeignKey` object.

column
  Can be a `schema.Column` object representing the relationship, or just its string name given as `tablename.columnname`. schema can be specified as `schema.tablename.columnname`.
constraint
  Is the owning `ForeignKeyConstraint` object, if any. if not given, then a `ForeignKeyConstraint` will be automatically created and added to the parent table.

column = property()
def copy(self)

Produce a copy of this ForeignKey object.

def get_referent(self, table)

return the column in the given table referenced by this `ForeignKey`, or None if this `ForeignKey` does not reference the given table.

def references(self, table)

Return True if the given table is referenced by this `ForeignKey`.

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### class ForeignKeyConstraint(Constraint)

Table-level foreign key constraint, represents a collection of `ForeignKey` objects.

def __init__(self, columns, refcolumns, name=None, onupdate=None, ondelete=None, use_alter=False)

Construct a new `ForeignKeyConstraint`.

def append_element(self, col, refcol)
def copy(self)
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### class Index(SchemaItem)

Represent an index of columns from a database table.

def __init__(self, name, *columns, **kwargs)

Construct an index object.

Arguments are:

name
  The name of the index
*columns
  Columns to include in the index. All columns must belong to the same table, and no column may appear more than once.
**kwargs

  Keyword arguments include:

  unique
    Defaults to False: create a unique index.
  postgres_where
    Defaults to None: create a partial index when using PostgreSQL

def append_column(self, column)
def create(self, bind=None)
def drop(self, bind=None)
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### class MetaData(SchemaItem)

A collection of Tables and their associated schema constructs.

Holds a collection of Tables and an optional binding to an `Engine` or `Connection`. If bound, the Table objects in the collection and their columns may participate in implicit SQL execution.

The `bind` property may be assigned to dynamically. A common pattern is to start unbound and then bind later when an engine is available:

    metadata = MetaData()
    # define tables
    Table('mytable', metadata, ...)
    # connect to an engine later, perhaps after loading a URL from a
    # configuration file
    metadata.bind = an_engine

MetaData is a thread-safe object after tables have been explicitly defined or loaded via reflection.

def __init__(self, bind=None, reflect=False)

Create a new MetaData object.

bind
  An Engine or Connection to bind to. May also be a string or URL instance, these are passed to create_engine() and this MetaData will be bound to the resulting engine.
reflect
  Optional, automatically load all tables from the bound database. Defaults to False. `bind` is required when this option is set. For finer control over loaded tables, use the `reflect` method of `MetaData`.

bind = property()

An Engine or Connection to which this MetaData is bound.

This property may be assigned an `Engine` or `Connection`, or assigned a string or URL to automatically create a basic `Engine` for this bind with `create_engine()`.

def clear(self)
def connect(*args, **kwargs)

Deprecated. Bind this MetaData to an Engine.

> Use `metadata.bind = <engine>` or `metadata.bind = <url>`.

> bind
>   A string, `URL`, `Engine` or `Connection` instance. If a string or `URL`, will be passed to `create_engine()` along with `\**kwargs` to produce the engine which to connect to. Otherwise connects directly to the given `Engine`.

def create_all(self, bind=None, tables=None, checkfirst=True)

Create all tables stored in this metadata.

This will conditionally create tables depending on if they do not yet exist in the database.

bind
  A `Connectable` used to access the database; if None, uses the existing bind on this `MetaData`, if any.
tables
  Optional list of `Table` objects, which is a subset of the total tables in the `MetaData` (others are ignored).

def drop_all(self, bind=None, tables=None, checkfirst=True)

Drop all tables stored in this metadata.

This will conditionally drop tables depending on if they currently exist in the database.

bind
  A `Connectable` used to access the database; if None, uses the existing bind on this `MetaData`, if any.
tables
  Optional list of `Table` objects, which is a subset of the total tables in the `MetaData` (others are ignored).

def is_bound(self)

True if this MetaData is bound to an Engine or Connection.

def reflect(self, bind=None, schema=None, only=None)

Load all available table definitions from the database.

Automatically creates `Table` entries in this `MetaData` for any table available in the database but not yet present in the `MetaData`. May be called multiple times to pick up tables recently added to the database, however no special action is taken if a table in this `MetaData` no longer exists in the database.

bind
  A `Connectable` used to access the database; if None, uses the existing bind on this `MetaData`, if any.
schema
  Optional, query and reflect tables from an alterate schema.
only

  Optional. Load only a sub-set of available named tables. May be specified as a sequence of names or a callable.

  If a sequence of names is provided, only those tables will be reflected. An error is raised if a table is requested but not available. Named tables already present in this `MetaData` are ignored.

  If a callable is provided, it will be used as a boolean predicate to filter the list of potential table names. The callable is called with a table name and this `MetaData` instance as positional arguments and should return a true value for any table to reflect.

def remove(self, table)
def table_iterator(self, reverse=True, tables=None)
def __contains__(self, key)
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### class PassiveDefault(DefaultGenerator)

A default that takes effect on the database side.

def __init__(self, arg, **kwargs)

Construct a new `PassiveDefault`.

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### class PrimaryKeyConstraint(Constraint)

def __init__(self, *columns, **kwargs)

Construct a new `PrimaryKeyConstraint`.

def add(self, col)
def append_column(self, col)
def copy(self)
def remove(self, col)
def __eq__(self, other)
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### class SchemaItem(object)

Base class for items that define a database schema.

bind = property()
def get_children(self, **kwargs)

used to allow SchemaVisitor access

info = property()
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### class SchemaVisitor(ClauseVisitor)

Define the visiting for `SchemaItem` objects.

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### class Sequence(DefaultGenerator)

Represents a named sequence.

def __init__(self, name, start=None, increment=None, schema=None, optional=False, quote=False, **kwargs)

Construct a new `Sequence`.

def create(self, bind=None, checkfirst=True)

Creates this sequence in the database.

def drop(self, bind=None, checkfirst=True)

Drops this sequence from the database.

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### class Table(SchemaItem,TableClause)

Represent a relational database table.

def __init__(self, name, metadata, *args, **kwargs)

Construct a Table.

Table objects can be constructed directly. Arguments are:

name

  The name of this table, exactly as it appears, or will appear, in the database.

  This property, along with the schema, indicates the singleton identity of this table.

  Further tables constructed with the same name/schema combination will return the same Table instance.

*args
  Should contain a listing of the Column objects for this table.
**kwargs

  kwargs include:

  schema
    The schema name for this table, which is required if the table resides in a schema other than the default selected schema for the engine's database connection. Defaults to `None`.
  autoload
    Defaults to False: the Columns for this table should be reflected from the database. Usually there will be no Column objects in the constructor if this property is set.
  autoload_with
    if autoload==True, this is an optional Engine or Connection instance to be used for the table reflection. If `None`, the underlying MetaData's bound connectable will be used.
  include_columns
    A list of strings indicating a subset of columns to be loaded via the `autoload` operation; table columns who aren't present in this list will not be represented on the resulting `Table` object. Defaults to `None` which indicates all columns should be reflected.
  info
    Defaults to {}: A space to store application specific data; this must be a dictionary.
  mustexist
    Defaults to False: indicates that this Table must already have been defined elsewhere in the application, else an exception is raised.
  useexisting
    Defaults to False: indicates that if this Table was already defined elsewhere in the application, disregard the rest of the constructor arguments.
  owner
    Defaults to None: optional owning user of this table. useful for databases such as Oracle to aid in table reflection.
  quote
    Defaults to False: indicates that the Table identifier must be properly escaped and quoted before being sent to the database. This flag overrides all other quoting behavior.
  quote_schema
    Defaults to False: indicates that the Namespace identifier must be properly escaped and quoted before being sent to the database. This flag overrides all other quoting behavior.

def append_column(self, column)

Append a `Column` to this `Table`.

def append_constraint(self, constraint)

Append a `Constraint` to this `Table`.

def create(self, bind=None, checkfirst=False)

Issue a `CREATE` statement for this table.

See also `metadata.create_all()`.

def drop(self, bind=None, checkfirst=False)

Issue a `DROP` statement for this table.

See also `metadata.drop_all()`.

def exists(self, bind=None)

Return True if this table exists.

def get_children(self, column_collections=True, schema_visitor=False, **kwargs)
key = property()
primary_key = property()
def tometadata(self, metadata, schema=None)

Return a copy of this `Table` associated with a different `MetaData`.

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### class ThreadLocalMetaData(MetaData)

A MetaData variant that presents a different `bind` in every thread.

Makes the `bind` property of the MetaData a thread-local value, allowing this collection of tables to be bound to different `Engine` implementations or connections in each thread.

The ThreadLocalMetaData starts off bound to None in each thread. Binds must be made explicitly by assigning to the `bind` property or using `connect()`. You can also re-bind dynamically multiple times per thread, just like a regular `MetaData`.

Use this type of MetaData when your tables are present in more than one database and you need to address them simultanesouly.

def __init__(self)

Construct a ThreadLocalMetaData.

Takes no arguments.

bind = property()

The bound Engine or Connection for this thread.

This property may be assigned an Engine or Connection, or assigned a string or URL to automatically create a basic Engine for this bind with `create_engine()`.

def connect(*args, **kwargs)

Deprecated. Bind to an Engine in the caller's thread.

> Use `metadata.bind=<engine>` or `metadata.bind=<url>`.

> bind
>   A string, `URL`, `Engine` or `Connection` instance. If a string or `URL`, will be passed to `create_engine()` along with `\**kwargs` to produce the engine which to connect to. Otherwise connects directly to the given `Engine`.

def dispose(self)

Dispose any and all `Engines` to which this `ThreadLocalMetaData` has been connected.

def is_bound(self)

True if there is a bind for this thread.

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### class UniqueConstraint(Constraint)

def __init__(self, *columns, **kwargs)

Construct a new `UniqueConstraint`.

def append_column(self, col)
def copy(self)
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