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Diffstat (limited to 'lib/python2.7/site-packages/SQLAlchemy-0.7.0-py2.7-linux-x86_64.egg/sqlalchemy/ext/compiler.py')
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diff --git a/lib/python2.7/site-packages/SQLAlchemy-0.7.0-py2.7-linux-x86_64.egg/sqlalchemy/ext/compiler.py b/lib/python2.7/site-packages/SQLAlchemy-0.7.0-py2.7-linux-x86_64.egg/sqlalchemy/ext/compiler.py deleted file mode 100755 index 7b083774..00000000 --- a/lib/python2.7/site-packages/SQLAlchemy-0.7.0-py2.7-linux-x86_64.egg/sqlalchemy/ext/compiler.py +++ /dev/null @@ -1,355 +0,0 @@ -# ext/compiler.py -# Copyright (C) 2005-2011 the SQLAlchemy authors and contributors <see AUTHORS file> -# -# This module is part of SQLAlchemy and is released under -# the MIT License: http://www.opensource.org/licenses/mit-license.php - -"""Provides an API for creation of custom ClauseElements and compilers. - -Synopsis -======== - -Usage involves the creation of one or more :class:`~sqlalchemy.sql.expression.ClauseElement` -subclasses and one or more callables defining its compilation:: - - from sqlalchemy.ext.compiler import compiles - from sqlalchemy.sql.expression import ColumnClause - - class MyColumn(ColumnClause): - pass - - @compiles(MyColumn) - def compile_mycolumn(element, compiler, **kw): - return "[%s]" % element.name - -Above, ``MyColumn`` extends :class:`~sqlalchemy.sql.expression.ColumnClause`, -the base expression element for named column objects. The ``compiles`` -decorator registers itself with the ``MyColumn`` class so that it is invoked -when the object is compiled to a string:: - - from sqlalchemy import select - - s = select([MyColumn('x'), MyColumn('y')]) - print str(s) - -Produces:: - - SELECT [x], [y] - -Dialect-specific compilation rules -================================== - -Compilers can also be made dialect-specific. The appropriate compiler will be -invoked for the dialect in use:: - - from sqlalchemy.schema import DDLElement - - class AlterColumn(DDLElement): - - def __init__(self, column, cmd): - self.column = column - self.cmd = cmd - - @compiles(AlterColumn) - def visit_alter_column(element, compiler, **kw): - return "ALTER COLUMN %s ..." % element.column.name - - @compiles(AlterColumn, 'postgresql') - def visit_alter_column(element, compiler, **kw): - return "ALTER TABLE %s ALTER COLUMN %s ..." % (element.table.name, element.column.name) - -The second ``visit_alter_table`` will be invoked when any ``postgresql`` dialect is used. - -Compiling sub-elements of a custom expression construct -======================================================= - -The ``compiler`` argument is the :class:`~sqlalchemy.engine.base.Compiled` -object in use. This object can be inspected for any information about the -in-progress compilation, including ``compiler.dialect``, -``compiler.statement`` etc. The :class:`~sqlalchemy.sql.compiler.SQLCompiler` -and :class:`~sqlalchemy.sql.compiler.DDLCompiler` both include a ``process()`` -method which can be used for compilation of embedded attributes:: - - from sqlalchemy.sql.expression import Executable, ClauseElement - - class InsertFromSelect(Executable, ClauseElement): - def __init__(self, table, select): - self.table = table - self.select = select - - @compiles(InsertFromSelect) - def visit_insert_from_select(element, compiler, **kw): - return "INSERT INTO %s (%s)" % ( - compiler.process(element.table, asfrom=True), - compiler.process(element.select) - ) - - insert = InsertFromSelect(t1, select([t1]).where(t1.c.x>5)) - print insert - -Produces:: - - "INSERT INTO mytable (SELECT mytable.x, mytable.y, mytable.z FROM mytable WHERE mytable.x > :x_1)" - -Cross Compiling between SQL and DDL compilers ---------------------------------------------- - -SQL and DDL constructs are each compiled using different base compilers - ``SQLCompiler`` -and ``DDLCompiler``. A common need is to access the compilation rules of SQL expressions -from within a DDL expression. The ``DDLCompiler`` includes an accessor ``sql_compiler`` for this reason, such as below where we generate a CHECK -constraint that embeds a SQL expression:: - - @compiles(MyConstraint) - def compile_my_constraint(constraint, ddlcompiler, **kw): - return "CONSTRAINT %s CHECK (%s)" % ( - constraint.name, - ddlcompiler.sql_compiler.process(constraint.expression) - ) - -Changing the default compilation of existing constructs -======================================================= - -The compiler extension applies just as well to the existing constructs. When overriding -the compilation of a built in SQL construct, the @compiles decorator is invoked upon -the appropriate class (be sure to use the class, i.e. ``Insert`` or ``Select``, instead of the creation function such as ``insert()`` or ``select()``). - -Within the new compilation function, to get at the "original" compilation routine, -use the appropriate visit_XXX method - this because compiler.process() will call upon the -overriding routine and cause an endless loop. Such as, to add "prefix" to all insert statements:: - - from sqlalchemy.sql.expression import Insert - - @compiles(Insert) - def prefix_inserts(insert, compiler, **kw): - return compiler.visit_insert(insert.prefix_with("some prefix"), **kw) - -The above compiler will prefix all INSERT statements with "some prefix" when compiled. - -.. _type_compilation_extension: - -Changing Compilation of Types -============================= - -``compiler`` works for types, too, such as below where we implement the MS-SQL specific 'max' keyword for ``String``/``VARCHAR``:: - - @compiles(String, 'mssql') - @compiles(VARCHAR, 'mssql') - def compile_varchar(element, compiler, **kw): - if element.length == 'max': - return "VARCHAR('max')" - else: - return compiler.visit_VARCHAR(element, **kw) - - foo = Table('foo', metadata, - Column('data', VARCHAR('max')) - ) - -Subclassing Guidelines -====================== - -A big part of using the compiler extension is subclassing SQLAlchemy -expression constructs. To make this easier, the expression and -schema packages feature a set of "bases" intended for common tasks. -A synopsis is as follows: - -* :class:`~sqlalchemy.sql.expression.ClauseElement` - This is the root - expression class. Any SQL expression can be derived from this base, and is - probably the best choice for longer constructs such as specialized INSERT - statements. - -* :class:`~sqlalchemy.sql.expression.ColumnElement` - The root of all - "column-like" elements. Anything that you'd place in the "columns" clause of - a SELECT statement (as well as order by and group by) can derive from this - - the object will automatically have Python "comparison" behavior. - - :class:`~sqlalchemy.sql.expression.ColumnElement` classes want to have a - ``type`` member which is expression's return type. This can be established - at the instance level in the constructor, or at the class level if its - generally constant:: - - class timestamp(ColumnElement): - type = TIMESTAMP() - -* :class:`~sqlalchemy.sql.expression.FunctionElement` - This is a hybrid of a - ``ColumnElement`` and a "from clause" like object, and represents a SQL - function or stored procedure type of call. Since most databases support - statements along the line of "SELECT FROM <some function>" - ``FunctionElement`` adds in the ability to be used in the FROM clause of a - ``select()`` construct:: - - from sqlalchemy.sql.expression import FunctionElement - - class coalesce(FunctionElement): - name = 'coalesce' - - @compiles(coalesce) - def compile(element, compiler, **kw): - return "coalesce(%s)" % compiler.process(element.clauses) - - @compiles(coalesce, 'oracle') - def compile(element, compiler, **kw): - if len(element.clauses) > 2: - raise TypeError("coalesce only supports two arguments on Oracle") - return "nvl(%s)" % compiler.process(element.clauses) - -* :class:`~sqlalchemy.schema.DDLElement` - The root of all DDL expressions, - like CREATE TABLE, ALTER TABLE, etc. Compilation of ``DDLElement`` - subclasses is issued by a ``DDLCompiler`` instead of a ``SQLCompiler``. - ``DDLElement`` also features ``Table`` and ``MetaData`` event hooks via the - ``execute_at()`` method, allowing the construct to be invoked during CREATE - TABLE and DROP TABLE sequences. - -* :class:`~sqlalchemy.sql.expression.Executable` - This is a mixin which should be - used with any expression class that represents a "standalone" SQL statement that - can be passed directly to an ``execute()`` method. It is already implicit - within ``DDLElement`` and ``FunctionElement``. - -Further Examples -================ - -"UTC timestamp" function -------------------------- - -A function that works like "CURRENT_TIMESTAMP" except applies the appropriate conversions -so that the time is in UTC time. Timestamps are best stored in relational databases -as UTC, without time zones. UTC so that your database doesn't think time has gone -backwards in the hour when daylight savings ends, without timezones because timezones -are like character encodings - they're best applied only at the endpoints of an -application (i.e. convert to UTC upon user input, re-apply desired timezone upon display). - -For Postgresql and Microsoft SQL Server:: - - from sqlalchemy.sql import expression - from sqlalchemy.ext.compiler import compiles - from sqlalchemy.types import DateTime - - class utcnow(expression.FunctionElement): - type = DateTime() - - @compiles(utcnow, 'postgresql') - def pg_utcnow(element, compiler, **kw): - return "TIMEZONE('utc', CURRENT_TIMESTAMP)" - - @compiles(utcnow, 'mssql') - def ms_utcnow(element, compiler, **kw): - return "GETUTCDATE()" - -Example usage:: - - from sqlalchemy import ( - Table, Column, Integer, String, DateTime, MetaData - ) - metadata = MetaData() - event = Table("event", metadata, - Column("id", Integer, primary_key=True), - Column("description", String(50), nullable=False), - Column("timestamp", DateTime, server_default=utcnow()) - ) - -"GREATEST" function -------------------- - -The "GREATEST" function is given any number of arguments and returns the one that is -of the highest value - it's equivalent to Python's ``max`` function. A SQL -standard version versus a CASE based version which only accommodates two -arguments:: - - from sqlalchemy.sql import expression - from sqlalchemy.ext.compiler import compiles - from sqlalchemy.types import Numeric - - class greatest(expression.FunctionElement): - type = Numeric() - name = 'greatest' - - @compiles(greatest) - def default_greatest(element, compiler, **kw): - return compiler.visit_function(element) - - @compiles(greatest, 'sqlite') - @compiles(greatest, 'mssql') - @compiles(greatest, 'oracle') - def case_greatest(element, compiler, **kw): - arg1, arg2 = list(element.clauses) - return "CASE WHEN %s > %s THEN %s ELSE %s END" % ( - compiler.process(arg1), - compiler.process(arg2), - compiler.process(arg1), - compiler.process(arg2), - ) - -Example usage:: - - Session.query(Account).\\ - filter( - greatest( - Account.checking_balance, - Account.savings_balance) > 10000 - ) - -"false" expression ------------------- - -Render a "false" constant expression, rendering as "0" on platforms that don't have a "false" constant:: - - from sqlalchemy.sql import expression - from sqlalchemy.ext.compiler import compiles - - class sql_false(expression.ColumnElement): - pass - - @compiles(sql_false) - def default_false(element, compiler, **kw): - return "false" - - @compiles(sql_false, 'mssql') - @compiles(sql_false, 'mysql') - @compiles(sql_false, 'oracle') - def int_false(element, compiler, **kw): - return "0" - -Example usage:: - - from sqlalchemy import select, union_all - - exp = union_all( - select([users.c.name, sql_false().label("enrolled")]), - select([customers.c.name, customers.c.enrolled]) - ) - -""" - -def compiles(class_, *specs): - def decorate(fn): - existing = class_.__dict__.get('_compiler_dispatcher', None) - existing_dispatch = class_.__dict__.get('_compiler_dispatch') - if not existing: - existing = _dispatcher() - - if existing_dispatch: - existing.specs['default'] = existing_dispatch - - # TODO: why is the lambda needed ? - setattr(class_, '_compiler_dispatch', lambda *arg, **kw: existing(*arg, **kw)) - setattr(class_, '_compiler_dispatcher', existing) - - if specs: - for s in specs: - existing.specs[s] = fn - - else: - existing.specs['default'] = fn - return fn - return decorate - -class _dispatcher(object): - def __init__(self): - self.specs = {} - - def __call__(self, element, compiler, **kw): - # TODO: yes, this could also switch off of DBAPI in use. - fn = self.specs.get(compiler.dialect.name, None) - if not fn: - fn = self.specs['default'] - return fn(element, compiler, **kw) - |