consys is a flexible tool to evaluate models using generic and readable constraints.

• Modern & Lightweight: consys has full TypeScript support and uses no additional dependencies, so it can easily be integrated.
• Customizable: Register custom functions and plugins, tailored to the application.
• Flexible: Constraints are designed to be as flexible as possible, while still being readable.
• User friendly: consys defines its own domain specific language to manage constraints, making it easy to read and fully generic.

Installation

consys is distributed via npm, it can be installed using the following command:

npm install consys

Quick start

After the installation, you can start using it. Here is a small example to get you started:

// First import the package
import {ConstraintSystem} from 'consys';

// This is our simple model, with an id and age entry
type TableRow = {
  id: number;
  entryAge: number;
};

// Now, lets create our constraint system
const rowConstraints = new ConstraintSystem<TableRow, {}>();

// For our constraint, we choose a simple assertion that must always be true:
rowConstraints.addConstraint({
  constraint: 'ALWAYS: $entryAge < 21',
  message: 'Row (id: $id): Age is $entryAge, but it must be 20 or lower.',
});

// Before we can evaluate something, we need to create some instances of our model
let rows: TableRow[] = [
  {id: 0, entryAge: 42},
  {id: 1, entryAge: 16},
  {id: 2, entryAge: 1337},
];

// Lets evaluate our model instance
let reports = rowConstraints.evaluate(rows, {});

for (let report of reports) {
  // Since we have only one constraint, there is only one evaluation
  let evaluation = report.evaluation[0];

  // Now print all errors
  if (!evaluation.consistent) {
    console.log(evaluation.message);
  }
}

Output:

>> Row (id: 0): Age is 42, but it must be 20 or lower.
>> Row (id: 2): Age is 1337, but it must be 20 or lower.

Documentation

For a more detailed look into all of the features, including the constraint syntax, custom functions, plugins and more, please have a look into the wiki.

Related packages

You might also want to take a look at consys-solver, which is a tool built upon consys that can find feasible models for constraint systems.

Contributors

The FireboltCasters