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//lib/python2.7/site-packages/alembic/ddl/base.py

import functools

from sqlalchemy import exc
from sqlalchemy import Integer
from sqlalchemy import types as sqltypes
from sqlalchemy.ext.compiler import compiles
from sqlalchemy.schema import Column
from sqlalchemy.schema import DDLElement
from sqlalchemy.sql.elements import quoted_name

from ..util import sqla_compat
from ..util.sqla_compat import _columns_for_constraint  # noqa
from ..util.sqla_compat import _find_columns  # noqa
from ..util.sqla_compat import _fk_spec  # noqa
from ..util.sqla_compat import _is_type_bound  # noqa
from ..util.sqla_compat import _table_for_constraint  # noqa

class AlterTable(DDLElement):

"""Represent an ALTER TABLE statement.

Only the string name and optional schema name of the table
    is required, not a full Table object.

"""

def __init__(self, table_name, schema=None):
        self.table_name = table_name
        self.schema = schema

class RenameTable(AlterTable):
    def __init__(self, old_table_name, new_table_name, schema=None):
        super(RenameTable, self).__init__(old_table_name, schema=schema)
        self.new_table_name = new_table_name

class AlterColumn(AlterTable):
    def __init__(
        self,
        name,
        column_name,
        schema=None,
        existing_type=None,
        existing_nullable=None,
        existing_server_default=None,
        existing_comment=None,
    ):
        super(AlterColumn, self).__init__(name, schema=schema)
        self.column_name = column_name
        self.existing_type = (
            sqltypes.to_instance(existing_type)
            if existing_type is not None
            else None
        )
        self.existing_nullable = existing_nullable
        self.existing_server_default = existing_server_default
        self.existing_comment = existing_comment

class ColumnNullable(AlterColumn):
    def __init__(self, name, column_name, nullable, **kw):
        super(ColumnNullable, self).__init__(name, column_name, **kw)
        self.nullable = nullable

class ColumnType(AlterColumn):
    def __init__(self, name, column_name, type_, **kw):
        super(ColumnType, self).__init__(name, column_name, **kw)
        self.type_ = sqltypes.to_instance(type_)

class ColumnName(AlterColumn):
    def __init__(self, name, column_name, newname, **kw):
        super(ColumnName, self).__init__(name, column_name, **kw)
        self.newname = newname

class ColumnDefault(AlterColumn):
    def __init__(self, name, column_name, default, **kw):
        super(ColumnDefault, self).__init__(name, column_name, **kw)
        self.default = default

class AddColumn(AlterTable):
    def __init__(self, name, column, schema=None):
        super(AddColumn, self).__init__(name, schema=schema)
        self.column = column

class DropColumn(AlterTable):
    def __init__(self, name, column, schema=None):
        super(DropColumn, self).__init__(name, schema=schema)
        self.column = column

class ColumnComment(AlterColumn):
    def __init__(self, name, column_name, comment, **kw):
        super(ColumnComment, self).__init__(name, column_name, **kw)
        self.comment = comment

@compiles(RenameTable)
def visit_rename_table(element, compiler, **kw):
    return "%s RENAME TO %s" % (
        alter_table(compiler, element.table_name, element.schema),
        format_table_name(compiler, element.new_table_name, element.schema),
    )

@compiles(AddColumn)
def visit_add_column(element, compiler, **kw):
    return "%s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        add_column(compiler, element.column, **kw),
    )

@compiles(DropColumn)
def visit_drop_column(element, compiler, **kw):
    return "%s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        drop_column(compiler, element.column.name, **kw),
    )

@compiles(ColumnNullable)
def visit_column_nullable(element, compiler, **kw):
    return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "DROP NOT NULL" if element.nullable else "SET NOT NULL",
    )

@compiles(ColumnType)
def visit_column_type(element, compiler, **kw):
    return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "TYPE %s" % format_type(compiler, element.type_),
    )

@compiles(ColumnName)
def visit_column_name(element, compiler, **kw):
    return "%s RENAME %s TO %s" % (
        alter_table(compiler, element.table_name, element.schema),
        format_column_name(compiler, element.column_name),
        format_column_name(compiler, element.newname),
    )

@compiles(ColumnDefault)
def visit_column_default(element, compiler, **kw):
    if sqla_compat.has_computed and (
        isinstance(element.default, sqla_compat.Computed)
        or isinstance(element.existing_server_default, sqla_compat.Computed)
    ):
        raise exc.CompileError(
            'Adding or removing a "computed" construct, e.g. GENERATED '
            "ALWAYS AS, to or from an existing column is not supported."
        )

return "%s %s %s" % (
        alter_table(compiler, element.table_name, element.schema),
        alter_column(compiler, element.column_name),
        "SET DEFAULT %s" % format_server_default(compiler, element.default)
        if element.default is not None
        else "DROP DEFAULT",
    )

def quote_dotted(name, quote):
    """quote the elements of a dotted name"""

if isinstance(name, quoted_name):
        return quote(name)
    result = ".".join([quote(x) for x in name.split(".")])
    return result

def format_table_name(compiler, name, schema):
    quote = functools.partial(compiler.preparer.quote)
    if schema:
        return quote_dotted(schema, quote) + "." + quote(name)
    else:
        return quote(name)

def format_column_name(compiler, name):
    return compiler.preparer.quote(name)

def format_server_default(compiler, default):
    return compiler.get_column_default_string(
        Column("x", Integer, server_default=default)
    )

def format_type(compiler, type_):
    return compiler.dialect.type_compiler.process(type_)

def alter_table(compiler, name, schema):
    return "ALTER TABLE %s" % format_table_name(compiler, name, schema)

def drop_column(compiler, name):
    return "DROP COLUMN %s" % format_column_name(compiler, name)

def alter_column(compiler, name):
    return "ALTER COLUMN %s" % format_column_name(compiler, name)

def add_column(compiler, column, **kw):
    return "ADD COLUMN %s" % compiler.get_column_specification(column, **kw)