pyquery-sagiv.oulu 0.0.1
A query string parsing library for REST server queries
License: MIT
Requires Python: >=3.6

# pyquery

Pyquery aims to ba a light weight fast parser written in pure Python, meant for use in REST API servers.
It was inspired by the [OData standard](https://www.odata.org/), but this query is a bit simpler and less feature rich.

## Goals
* An easily extendable querying syntax
* Be able to query any data source by writing a simple translator
* Usable in any Python REST framework


## Example usage

Here is an example of the most basic usage
```python
from pyquery.encoder.common import encoder
from pyquery.translator import mongo_translator

# The raw input expression
expression = r"((age gt 20) and (age ge 10))"

# Generate the encoded expression
encoded_expression = encoder.encode_expression(expression)
print(encoded_expression)

# Translate into a mongo query
mongo_query = mongo_translator.translate(encoded_expression)
print(mongo_query)
```

This uses the default pre built expression encoding elements & the pre build
translation elements. you can add additional elements like this:
```python
from pyquery.encoder.common import encoder
from pyquery.encoder import BooleanOperation, BinaryOperation
from pyquery.translator import mongo_translator


@encoder.register_binary_logical_operator('xor')
class Xor(BooleanOperation):
    pass


@encoder.register_ratio('contains')
class Contains(BinaryOperation):
    pass


# The raw input expression
expression = r"((age gt 20) xor (name contains 'subtext'))"

# Generate the encoded expression
encoded_expression = encoder.encode_expression(expression)
print(encoded_expression)

# Translate into a mongo query
mongo_query = mongo_translator.translate(encoded_expression)
print(mongo_query)
```

If you want you can forgo the pre loaded encoder & translator objects and create ones of your one with completely custom elements:

```python
from pyquery.encoder import Encoder
from pyquery.encoder import BooleanOperation, BinaryOperation

from pyquery.translator import MongoTranslator

encoder = Encoder()


# Register encoders
@encoder.register_binary_logical_operator('and')
class And(BooleanOperation):
    pass


@encoder.register_ratio('eq')
class Equals(BinaryOperation):
    pass


mongo_translator = MongoTranslator()

# Register translators
@mongo_translator.register_boolean_operation_translator(And)
def translate_and(operation: And, translator: MongoTranslator):
    return {
        '$and': [
            translator.translate(operand) for operand in operation.operands
        ]
    }


@mongo_translator.register_binary_operation_translator(Equals)
def translate_equals(operation: Equals):
    return {
        operation.field.name: {
            '$eq': operation.value
        }
    }

expression = '((name eq "eric") and (age eq 18))'

# Generate the encoded expression
encoded_expression = encoder.encode_expression(expression)
print(encoded_expression)

# Translate into a mongo query
mongo_query = mongo_translator.translate(encoded_expression)
print(mongo_query)
```

## Limitations
* Expressions can only be parentheses complete (for now).
For example, these expressions are not allowed:
* ```age gt 10 and name eq "eric" and city eq "tlv"```
* ```(age gt 10 and name eq "eric" and city eq "tlv")```
* ```(age gt 10) and (name eq "eric") and (city eq "tlv")```\
But this expression is valid:\
```(((age gt 10) and (name eq "eric")) and (city eq "tlv"))```
* You cannot register new value types (for now), you must use the prebuilt boolean, string or number values

## Encoder Translator design
This utility is seperated into two parts: Encoder & Translator

### Encoder
The encoder is responsible for parsing the input string into a structured expression object, 
that can be easily read & parsed by code

The encoder can encodes grammar elements that are registered to it. each registered grammar is a 
ratio between a field & a value, or a logical operation between two logical values or expressions 

### Translator
The translator translates the generic expression format given from the encoder into a target language.\
There is a basic mongo translator built into this package (more yet to come), but you can easily write 
a translator of your own.

## Contributors
* Sagiv Oulu