=== PQL

PQL stands for Python-Query-Language. PQL translates python expressions to MongoDB queries.

PQL uses the builtin python ast module for parsing and analysis of python expressions.

PQL is resilient to code injections as it doesn't evaluate the code.

Installation

pip install pql

Follow @alonhorev on twitter for updates. Source located at: http://github.com/alonho/pql

Find Queries

Schema-Free Example

The schema-free parser converts python expressions to mongodb queries with no schema enforcment:

>>> import pql
>>> pql.find("a > 1 and b == 'foo' or not c.d == False")
{'$or': [{'$and': [{'a': {'$gt': 1}}, {'b': 'foo'}]}, {'$not': {'c.d': False}}]}

Schema-Aware Example

The schema-aware parser validates fields exist:

>>> import pql
>>> pql.find('b == 1', schema={'a': pql.DateTimeField()}) 
Traceback (most recent call last):
	...
pql.ParseError: Field not found: b. options: ['a']

Validates values are of the correct type:

>>> pql.find('a == 1', schema={'a': pql.DateTimeField()})
Traceback (most recent call last):
	...
pql.ParseError: Unsupported syntax (Num).

Validates functions are called against the appropriate types:

>>> pql.find('a == regex("foo")', schema={'a': pql.DateTimeField()})
Traceback (most recent call last):
	...
pql.ParseError: Unsupported function (regex). options: ['date', 'exists', 'type']

Data Types

pql	mongo
a == 1	{'a': 1}
a == "foo"	{'a': 'foo'}
a == None	{'a': None}
a == True	{'a': True}
a == False	{'a': False}
a == [1, 2, 3]	{'a': [1, 2, 3]}
a == {"foo": 1}	{'a': {'foo': 1}}
a == date("2012-3-4")	{'a': datetime.datetime(2012, 3, 4, 0, 0)}
a == date("2012-3-4 12:34:56")	{'a': datetime.datetime(2012, 3, 4, 12, 34, 56)}
a == date("2012-3-4 12:34:56,123")	{'a': datetime.datetime(2012, 3, 4, 12, 34, 56, 123000)}
id == id("abcdeabcdeabcdeabcdeabcd")	{'id': bson.ObjectId("abcdeabcdeabcdeabcdeabcd")}

Operators

pql	mongo
a != 1	{'a': {'$ne': 1}}
a > 1	{'a': {'$gt': 1}}
a >= 1	{'a': {'$gte': 1}}
a < 1	{'a': {'$lt': 1}}
a <= 1	{'a': {'$lte': 1}}
a in [1, 2, 3]	{'a': {'$in': [1, 2, 3]}}
a not in [1, 2, 3]	{'a': {'$nin': [1, 2, 3]}}

Boolean Logic

pql	mongo
not a == 1	{'$not': {'a': 1}}
a == 1 or b == 2	{'$or': [{'a': 1}, {'b': 2}]}
a == 1 and b == 2	{'$and': [{'a': 1}, {'b': 2}]}

Functions

pql	mongo
a == all([1, 2, 3])	{'a': {'$all': [1, 2, 3]}}
a == exists(True)	{'a': {'$exists': True}}
a == match({"foo": "bar"})	{'a': {'$elemMatch': {'foo': 'bar'}}}
a == mod(10, 3)	{'a': {'$mod': [10, 3]}}
a == regex("foo")	{'a': {'$regex': 'foo'}}
a == regex("foo", "i")	{'a': {'$options': 'i', '$regex': 'foo'}}
a == size(4)	{'a': {'$size': 4}}
a == type(3)	{'a': {'$type': 3}}

Aggregation Queries

Example

Lets say you have a collection of car listings:

>>> list(db.cars.find())
[{'_id': ObjectId('51794ce58c998f1e2b654b50'),
  'made_on': datetime.datetime(1971, 4, 7, 0, 0),
  'model': 'fiat',
  'price': 3},
 {'_id': ObjectId('51794cea8c998f1e2b654b51'),
  'made_on': datetime.datetime(1980, 10, 19, 0, 0),
  'model': 'subaru',
  'price': 5},
 {'_id': ObjectId('51794cf08c998f1e2b654b52'),
  'made_on': datetime.datetime(1983, 2, 27, 0, 0),
  'model': 'kia',
  'price': 4},
 {'_id': ObjectId('51794d3c8c998f1e2b654b53'),
  'made_on': datetime.datetime(1988, 1, 23, 0, 0),
  'model': 'kia',
  'price': 7}]

How do you get the number of cars and the sum of their prices per model per decade:

>>> collection.aggregate(project(model='model', 
                                made_on='year(made_on)', 
								price='price * 3.7') | 
		                 match('made_on > 1975 and made_on < 1990') | 
						 group(_id=project(model='model', 
						                   decade='made_on - (made_on % 10)'), 
					           count='sum(1)', 
							   total='sum(price)'))
{'ok': 1.0,
 'result': [{'_id': {'decade': 1980, 'model': 'subaru'}, 'count': 1,'total': 18.5},
		    {'_id': {'decade': 1980, 'model': 'kia'}, 'count': 2, 'total': 40.7}]}

How would it look using the raw syntax:

[{'$project': {'made_on': {'$year': '$made_on'},
               'model': '$model',
               'price': {'$multiply': ['$price', 3.7]}}},
 {'$match': {'$and': [{'made_on': {'$gt': 1975}},
                      {'made_on': {'$lt': 1990}}]}},
 {'$group': {'_id': {'decade': {'$subtract': ['$made_on',
                                              {'$mod': ['$made_on', 10]}]},
                     'model': '$model'},
  'count': {'$sum': 1},
  'total': {'$sum': '$price'}}}]

Referencing Fields

pql	mongo
a	$a
a.b.c	$a.b.c

Arithmetic Operators

pql	mongo
a + 1	{'$add': ['$a', 1]}
a / 1	{'$divide': ['$a', 1]}
a % 1	{'$mod': ['$a', 1]}
a * 1	{'$multiply': ['$a', 1]}
a - 1	{'$subtract': ['$a', 1]}
a > 0	{'$gt': ['$a', 0]}
a >= 0	{'$gte': ['$a', 0]}
a < 0	{'$lt': ['$a', 0]}
a <= 0	{'$lte': ['$a', 0]}

Logical Operators

pql	mongo
a == 0	{'$eq': ['$a', 0]}
a != 0	{'$ne': ['$a', 0]}
cmp(a, "bar")	{'$cmp': ['$a', 'bar']}
a and b	{'$and': ['$a', '$b']}
not a	{'$not': '$a'}
a or b	{'$or': ['$a', '$b']}
a if b > 3 else c	{'$cond': [{'$gt': ['$b', 3]}, '$a', '$c']}
ifnull(a + b, 100)	{'$ifnull': [{'$add': ['$a', '$b']}, 100]}

Date Operators

pql	mongo
dayOfYear(a)	{'$dayOfYear': '$a'}
dayOfMonth(a)	{'$dayOfMonth': '$a'}
dayOfWeek(a)	{'$dayOfWeek': '$a'}
year(a)	{'$year': '$a'}
month(a)	{'$month': '$a'}
week(a)	{'$week': '$a'}
hour(a)	{'$hour': '$a'}
minute(a)	{'$minute': '$a'}
second(a)	{'$second': '$a'}
millisecond(a)	{'$millisecond': '$a'}

String Operators

pql	mongo
concat("foo", "bar", b)	{'$concat': ['foo', 'bar', '$b']}
strcasecmp("foo", b)	{'$strcasecmp': ['foo', '$b']}
substr("foo", 1, 2)	{'$substr': ['foo', 1, 2]}
toLower(a)	{'$toLower': '$a'}
toUpper(a)	{'$toUpper': '$a'}

TODO

Generate a schema from a mongoengine or mongokit class.
Add a declarative schema generation syntax.
Add support for geospatial queries.
Add support for $where.

lbosson/pql