SQLAlchemy:打印实际查询

Question

我真的希望能够为我的应用程序打印出有效的SQL,包括值,而不是绑定参数,但是在SQLAlchemy中如何做到这一点并不明显(按照设计,我很确定).

有没有人以一般方式解决这个问题？

Answer 1

在绝大多数情况下,SQLAlchemy语句或查询的"字符串化"非常简单:

print str(statement)

这既适用于ORM Query,也适用于任何select()或其他声明.

注意:sqlalchemy文档中正在维护以下详细解答.

要将语句编译为特定的方言或引擎,如果语句本身尚未绑定到语句本身,则可以将其传递给compile():

print statement.compile(someengine)

或没有引擎:

from sqlalchemy.dialects import postgresql
print statement.compile(dialect=postgresql.dialect())

给定一个ORM Query对象时,为了获得该compile()方法,我们只需要首先访问.statement访问器:

statement = query.statement
print statement.compile(someengine)

关于绑定参数将被"内联"到最终字符串中的原始规定,这里的挑战是SQLAlchemy通常不会对此进行任务,因为这是由Python DBAPI适当处理的,更不用说绕过绑定参数了可能是现代Web应用程序中利用最广泛的安全漏洞.SQLAlchemy在某些情况下执行此字符串化的能力有限,例如发出DDL.为了访问此功能,可以使用'literal_binds'标志,传递给compile_kwargs:

from sqlalchemy.sql import table, column, select

t = table('t', column('x'))

s = select([t]).where(t.c.x == 5)

print s.compile(compile_kwargs={"literal_binds": True})

上述方法有一些注意事项,它只支持基本类型,例如int和字符串,而且如果bindparam 没有直接使用预设值,它也将无法对其进行字符串化.

要支持不支持的类型的内联文字呈现,请为TypeDecorator包含TypeDecorator.process_literal_param方法的目标类型 实现a :

from sqlalchemy import TypeDecorator, Integer


class MyFancyType(TypeDecorator):
    impl = Integer

    def process_literal_param(self, value, dialect):
        return "my_fancy_formatting(%s)" % value

from sqlalchemy import Table, Column, MetaData

tab = Table('mytable', MetaData(), Column('x', MyFancyType()))

print(
    tab.select().where(tab.c.x > 5).compile(
        compile_kwargs={"literal_binds": True})
)

产生如下输出:

SELECT mytable.x
FROM mytable
WHERE mytable.x > my_fancy_formatting(5)

Answer 2

这适用于python 2和3,并且比以前更清晰,但需要SA> = 1.0.

from sqlalchemy.engine.default import DefaultDialect
from sqlalchemy.sql.sqltypes import String, DateTime, NullType

# python2/3 compatible.
PY3 = str is not bytes
text = str if PY3 else unicode
int_type = int if PY3 else (int, long)
str_type = str if PY3 else (str, unicode)


class StringLiteral(String):
    """Teach SA how to literalize various things."""
    def literal_processor(self, dialect):
        super_processor = super(StringLiteral, self).literal_processor(dialect)

        def process(value):
            if isinstance(value, int_type):
                return text(value)
            if not isinstance(value, str_type):
                value = text(value)
            result = super_processor(value)
            if isinstance(result, bytes):
                result = result.decode(dialect.encoding)
            return result
        return process


class LiteralDialect(DefaultDialect):
    colspecs = {
        # prevent various encoding explosions
        String: StringLiteral,
        # teach SA about how to literalize a datetime
        DateTime: StringLiteral,
        # don't format py2 long integers to NULL
        NullType: StringLiteral,
    }


def literalquery(statement):
    """NOTE: This is entirely insecure. DO NOT execute the resulting strings."""
    import sqlalchemy.orm
    if isinstance(statement, sqlalchemy.orm.Query):
        statement = statement.statement
    return statement.compile(
        dialect=LiteralDialect(),
        compile_kwargs={'literal_binds': True},
    ).string

演示:

# coding: UTF-8
from datetime import datetime
from decimal import Decimal

from literalquery import literalquery


def test():
    from sqlalchemy.sql import table, column, select

    mytable = table('mytable', column('mycol'))
    values = (
        5,
        u'snowman: ?',
        b'UTF-8 snowman: \xe2\x98\x83',
        datetime.now(),
        Decimal('3.14159'),
        10 ** 20,  # a long integer
    )

    statement = select([mytable]).where(mytable.c.mycol.in_(values)).limit(1)
    print(literalquery(statement))


if __name__ == '__main__':
    test()

给出了这个输出:(在python 2.7和3.4中测试过)

SELECT mytable.mycol
FROM mytable
WHERE mytable.mycol IN (5, 'snowman: ?', 'UTF-8 snowman: ?',
      '2015-06-24 18:09:29.042517', 3.14159, 100000000000000000000)
 LIMIT 1

Answer 3

鉴于您想要的只在调试时才有意义,您可以启动SQLAlchemy echo=True,以记录所有SQL查询.例如:

engine = create_engine(
    "mysql://scott:tiger@hostname/dbname",
    encoding="latin1",
    echo=True,
)

这也可以仅针对单个请求进行修改:

echo=False- 如果True,引擎会将所有语句repr()及其参数列表记录到引擎记录器中,默认为sys.stdout.所述echo的属性Engine可以在任何时间进行修改,以打开记录和关闭.如果设置为字符串"debug",结果行也将打印到标准输出.此标志最终控制Python记录器; 有关如何直接配置日志记录的信息,请参阅配置日志记录.

来源:SQLAlchemy Engine配置

如果与Flask一起使用,您只需设置即可

app.config["SQLALCHEMY_ECHO"] = True

得到相同的行为.

Answer 4

我们可以使用编译方法来达到这个目的.来自文档:

from sqlalchemy.sql import text
from sqlalchemy.dialects import postgresql

stmt = text("SELECT * FROM users WHERE users.name BETWEEN :x AND :y")
stmt = stmt.bindparams(x="m", y="z")

print(stmt.compile(dialect=postgresql.dialect(),compile_kwargs={"literal_binds": True}))

结果:

SELECT * FROM users WHERE users.name BETWEEN 'm' AND 'z'

Answer 5

因此,在@zzzeek对@ bukzor代码的评论的基础上,我想出了这个,以便轻松获得"非常可打印"的查询:

def prettyprintable(statement, dialect=None, reindent=True):
    """Generate an SQL expression string with bound parameters rendered inline
    for the given SQLAlchemy statement. The function can also receive a
    `sqlalchemy.orm.Query` object instead of statement.
    can 

    WARNING: Should only be used for debugging. Inlining parameters is not
             safe when handling user created data.
    """
    import sqlparse
    import sqlalchemy.orm
    if isinstance(statement, sqlalchemy.orm.Query):
        if dialect is None:
            dialect = statement.session.get_bind().dialect
        statement = statement.statement
    compiled = statement.compile(dialect=dialect,
                                 compile_kwargs={'literal_binds': True})
    return sqlparse.format(str(compiled), reindent=reindent)

我个人很难读取没有缩进的代码,所以我习惯于sqlparse重新编写SQL.它可以安装pip install sqlparse.

Answer 6

此代码基于@bukzor 现有的精彩答案.我刚刚将自定义渲染datetime.datetime类型添加到Oracle中TO_DATE().

随意更新代码以适合您的数据库:

import decimal
import datetime

def printquery(statement, bind=None):
    """
    print a query, with values filled in
    for debugging purposes *only*
    for security, you should always separate queries from their values
    please also note that this function is quite slow
    """
    import sqlalchemy.orm
    if isinstance(statement, sqlalchemy.orm.Query):
        if bind is None:
            bind = statement.session.get_bind(
                    statement._mapper_zero_or_none()
            )
        statement = statement.statement
    elif bind is None:
        bind = statement.bind 

    dialect = bind.dialect
    compiler = statement._compiler(dialect)
    class LiteralCompiler(compiler.__class__):
        def visit_bindparam(
                self, bindparam, within_columns_clause=False, 
                literal_binds=False, **kwargs
        ):
            return super(LiteralCompiler, self).render_literal_bindparam(
                    bindparam, within_columns_clause=within_columns_clause,
                    literal_binds=literal_binds, **kwargs
            )
        def render_literal_value(self, value, type_):
            """Render the value of a bind parameter as a quoted literal.

            This is used for statement sections that do not accept bind paramters
            on the target driver/database.

            This should be implemented by subclasses using the quoting services
            of the DBAPI.

            """
            if isinstance(value, basestring):
                value = value.replace("'", "''")
                return "'%s'" % value
            elif value is None:
                return "NULL"
            elif isinstance(value, (float, int, long)):
                return repr(value)
            elif isinstance(value, decimal.Decimal):
                return str(value)
            elif isinstance(value, datetime.datetime):
                return "TO_DATE('%s','YYYY-MM-DD HH24:MI:SS')" % value.strftime("%Y-%m-%d %H:%M:%S")

            else:
                raise NotImplementedError(
                            "Don't know how to literal-quote value %r" % value)            

    compiler = LiteralCompiler(dialect, statement)
    print compiler.process(statement)

Answer 7

要使用 Python 日志记录而不是标志来记录 SQL 查询echo=True：

import logging

logging.basicConfig()
logging.getLogger('sqlalchemy.engine').setLevel(logging.INFO)

根据文档。

Answer 8

我想指出的是，以上给出的解决方案不适用于非平凡的查询。我遇到的一个问题是更复杂的类型，例如导致问题的pgsql ARRAY。我确实找到了一个对我来说甚至可以与pgsql ARRAY一起使用的解决方案：

借用：https : //gist.github.com/gsakkis/4572159

链接的代码似乎基于旧版本的SQLAlchemy。您会收到一条错误消息，指出_mapper_zero_or_none属性不存在。这是一个更新的版本，将与较新的版本一起使用，您只需将_mapper_zero_or_none替换为bind即可。此外，它还支持pgsql数组：

# adapted from:
# https://gist.github.com/gsakkis/4572159
from datetime import date, timedelta
from datetime import datetime

from sqlalchemy.orm import Query


try:
    basestring
except NameError:
    basestring = str


def render_query(statement, dialect=None):
    """
    Generate an SQL expression string with bound parameters rendered inline
    for the given SQLAlchemy statement.
    WARNING: This method of escaping is insecure, incomplete, and for debugging
    purposes only. Executing SQL statements with inline-rendered user values is
    extremely insecure.
    Based on http://stackoverflow.com/questions/5631078/sqlalchemy-print-the-actual-query
    """
    if isinstance(statement, Query):
        if dialect is None:
            dialect = statement.session.bind.dialect
        statement = statement.statement
    elif dialect is None:
        dialect = statement.bind.dialect

    class LiteralCompiler(dialect.statement_compiler):

        def visit_bindparam(self, bindparam, within_columns_clause=False,
                            literal_binds=False, **kwargs):
            return self.render_literal_value(bindparam.value, bindparam.type)

        def render_array_value(self, val, item_type):
            if isinstance(val, list):
                return "{%s}" % ",".join([self.render_array_value(x, item_type) for x in val])
            return self.render_literal_value(val, item_type)

        def render_literal_value(self, value, type_):
            if isinstance(value, long):
                return str(value)
            elif isinstance(value, (basestring, date, datetime, timedelta)):
                return "'%s'" % str(value).replace("'", "''")
            elif isinstance(value, list):
                return "'{%s}'" % (",".join([self.render_array_value(x, type_.item_type) for x in value]))
            return super(LiteralCompiler, self).render_literal_value(value, type_)

    return LiteralCompiler(dialect, statement).process(statement)

已测试到两个级别的嵌套数组。