Value Constraints

Sometimes you need more control over the values that are valid in your data model. For these cases Temple provides a suite of Value Constraints: extra metadata you can attach to properties that allow values to be restricted in some way.

Primitive Restrictions

Many of Temple's primitive data types support optional parameters when you declare them, to give bounds on their values. An example of this is when an integer is defined. We'll take the ExampleService from the Getting Started guide:

ExampleService: service {
  foo: string;
  bar: int;
}

If, for example, we wanted to constrain the bar property to be only positive numbers, we could write:

ExampleService: service {
  foo: string;
  bar: int(min: 0);
}

If we wanted to restrict it between two numbers, for example 0 and 100, we'd write:

ExampleService: service {
  foo: string;
  bar: int(100, 0);
}

Notice that here we didn't provide the argument names to the int definitions, as they're optional. However, when only a single argument is provided to the int definition, it defaults to the max argument. By using the min: name, we can specify the min without the max. Most of the primitives in Temple support similar parameters. The full list of parameters can be found in the Primitives section of the Templefile reference.