Configuration System

Using the Configuration System

A framework is provided to make configurability easier for developers and configuring easier for implementers.

To learn how to configure your distro, see the Implementer Documentation.

How to make a frontend module configurable

You should use the OpenMRS Frontend Framework to make modules configurable.

The main task is to create a config schema for your module. The config schema is what tells the framework what configuration files should look like, including defaults and validations.

Designing a schema

You’ll probably start with some idea of what you want configs for your module to look like. Try and put yourself in the implementer’s shoes and imagine what features they will expect to be configurable, and what they might expect the configuration property to be called. Assume they don’t know anything about the internal workings of your module.

By way of example, let’s say we’re building a module for a virtual provider functionality at a very futuristic hospital. Maybe we want an implementer to be able to write the following in their config file:

"@openmrs/esm-hologram-doctor": {
  "hologram": {
    "color": true
  },
  "virtualProvider": {
    "name": {
      "given": ["Qui", "Gon"]
    }
  },
  "robots": [
    { "name": "R2-D2", "homeworld": "Naboo" },
    { "name": "BB-8", "homeworld": "Hosnian Prime" }
  ]
}

In the following section, we’ll see how to write a config schema that supports these config elements.

Defining a schema

We’ll start with just that first nested config element from above, hologram.color. We must provide defaults for all of the values—in OpenMRS Frontend 3.0, all configuration is optional. All modules should do something reasonable out of the box.

import { defineConfigSchema, Type } from "@openmrs/esm-framework"
 
defineConfigSchema("@openmrs/esm-hologram-doctor", {
  hologram: {
    color: {
      _type: Type.Boolean,
      _default: false,
      _description: "Whether the hologram supports color display."
    }
  }
}

Note that each configuration element should have an object for a value, and that this object must define the properties for that element. Do not do this:

❌ // This is wrong!
❌ defineConfigSchema("@openmrs/esm-hologram-doctor",
❌  hologram: {
❌   salutation: "Some friendly default salutation! ? this is wrong!"
❌ })

The words prefixed with _ are schema keywords. Do not prefix the names of your config elements with underscores. Especially do not use a schema keyword as a config element name.

Typing

While not strictly required in the current version, you should provide a type for every config element you define. The _type keyword accepts values from the Type enum.

These types are used both to validate input and to support special behavior in the implementer tools.

Validators

You should provide validators for your configuration elements wherever possible. This reduces the probability that implementers using your module will have hard-to-debug runtime errors. It gives you, the module developer, the opportunity to provide implementers with very helpful explanations about why their configuration doesn’t work.

A validator can be created using the validator function, as above.

The first argument is a function that takes the config value as its only argument. If the function returns something truthy, validation passes. If the function returns something falsy, an error is thrown with the second argument as an explanation.

You can even validate nested objects:

For convenience, some common validators are provided out of the box. See the API / validators docs.

Arrays

You can accept and validate arrays, and arrays containing objects, in your configuration schema. This is configured with the elements parameter, used with _type: Type.Array. For example, a schema which would accept an array of strings up to 30 characters long would look like this:

Here is an example of a schema that expects an array of objects structured in a particular way.

This schema will require that any objects in the robots array must only have the keys name and homeworld, and that name is required.

Objects within arrays do not have to have defaults. If an object is supplied to the robots array that does not have a name, an error will be thrown.

Using config values

The generic way

The config is fetched asynchronously using getConfig(moduleName). Continuing the above example, we would have something like:

The content of config will be pulled from the config files, falling back to the defaults for configuration elements for which no values have been provided.

React support

A React Hook is provided to hide the asynchronicity of config loading. The moduleName provided in your app's root index.ts file (to the functions getSyncLifecycle or getAsyncLifecycle) is used to look up the configuration elsewhere in the application.

You can then get the config tree as an object using the useConfig React hook.

The content of config will be pulled from the config files, falling back to the defaults for configuration elements for which no values have been provided.

Support in other frameworks (Angular, Vue, Svelte, etc.)

This hasn’t been implemented yet, but you are welcome to implement it! See Contributing.

Typing

It is nice to be able to have type validation for your use of configuration. To accomplish this, define an interface alongside your config schema.

You can then use this typing information when calling the config functions:

Schema Reference

_default

All config elements must have a default (excluding elements within arrays of objects).

The default does not necessarily need to satisfy the _type or the _validators of the element, but this may change in future versions.

_type

One of the values from the Type enum. Used for validation and to help the implementer tools work with the element.

Should always appear alongside _default.

_description

Helps implementers understand what the configuration element actually does and how it is intended to be used.

Can be used anywhere within the schema structure.

_validators

An array of validator objects.

Some common validators are provided: API / validators.

Custom validators should be created with the validator function.

Can be used anywhere within the schema structure.

_elements

Only valid alongside _type_: Type.Array. A _default must also be provided at this level. Value should be a schema for the values contained in the array.

API Documentation

See the Config Functions section of the API docs.

The RFC

This package was established as the result of RFC #14. This document provides the rationale and guiding principles of the configuration system.