TemplateFunctions.md

Template Functions

The way to query a Jinaga application is to write a template function. This is a function that returns the shape of a JSON fact. It takes one parameter, which is the predecessor of the fact.

function templateFunction(predecessor) {
  return {
    type: 'MyApp.Type',
    role: predecessor
  };
}

Use template functions with j.watch, j.query, j.where, and j.not. The template will match all facts that have the specified constant values (conventionally used for type), and the predecessor in the specified role.

Conditions

To limit the matching facts based on their successors, define a second template function. If any facts match the template, then the condition is true.

function hasChild(p) {
  return {
    type: 'MyApp.Child',
	parent: p
  };
}

Use a condition in a template function by passing it to j.where.

function templateFunction(predecessor) {
  return j.where({
    type: 'MyApp.Type',
    role: predecessor
  }, [hasChild]);
}

Negating conditions

You can negate a condition within the function itself using j.not.

function hasNoChild(p) {
  return j.not({
    type: 'MyApp.Child',
	parent: p
  });
}

Or you can negate the condition when using the function.

function templateFunction(predecessor) {
  return j.where({
    type: 'MyApp.Type',
    role: predecessor
  }, [j.not(hasChild)]);
}