Sifter

Sifter is the lightweight C++ library, providing container for a filter.

Motivation

Let's imagine there is some repository-object. It allows to select the list of entities in according to some filter - set of conditions, joined by AND or OR operators. Number of conditions in this filter may vary: filter may be empty, may contain a single condition or several ones.

There is also something, which uses this repository. For example, it may be some REST API handler. It should transform requested URL into filter for repository to send in response the list of entities, satisfying this filter.

Sifter provides a possible solution for this task.

Requirements

C++17 or C++11 plus Boost v1.71 or later

Terminology

Sifter provides two kinds of objects: condition and filter.

Condition

Condition contains three fields:

left value;
right value;
comparison operator.

In sifter this object is represented by sifter::basic_condition variadic template. The first template parameter - is comparison operator. It is assumed that it is some enumiration. The second template parameter - is default value of comparison, used in constructor. All other parameters are used in std::variant for left and right values.

Library provides also sifter::comparison comparison type and sifter::condition template - sifter::basic_condition template, specialized by sifter::comparison type.

Filter

Filter is tree. It's left and right nodes are conditions or other filters. Filter contains also logic operator (AND or OR) of sifter::operation type.

Filter is represented by sifter::basic_filter variadic template. It has the same parameters as sifter::basic_condition template. Filter, specialized by sifter::comparison type, is represented by sifter::filter type.

Example

#include <sifter/filter.hpp>
...

enum field
{
    id,
    name,
    age
};

using condition = sifter::condition<field, int, std::string>;
using filter = sifter::filter<field, int, std::string>;

...

filter f = condition(id) < 10 && (condition(name) % "John%" || condition(age) == 20);
std::vector<entity> entities = repository.get(f);

Installation

mkdir build
cd build
cmake ..
make
make test
sudo make install

If you would like to avoid testing and building of examples you can run cmake with these arguments:

...
cmake -DBUILD_TESTING=OFF -DBUILD_EXAMPLES=OFF ..
...