Custom hooks

• Start Date: 2020-03-08
• Target Version: 0.14
• Reference Issues: -
• Implementation PR: -

Summary

We should extend the current Action Hooks feature. It is used by the ActionHook middleware and it can be defined only before, after & error hooks for actions.

For some major components, it would be good if the user can define custom hooks for the custom functions, e.g. define a beforeTransform or afterPopulate hook in moleculer-db.

Basic example

module.exports = {
    name: "posts",
    mixins: [DbService],
    hooks: {
        // It will be called before transforming
        beforeTransform(ctx, params, doc) {
            doc.id = encrypt(doc._id);
            delete doc._id;
        },

        // It will be called after populating
        afterPopulate(ctx, populate, doc) {
            if (doc.author) {
                delete doc.authorID;
            }
        }
    },
};

function transformDocuments(ctx, params, doc) {
  // Call beforeTransform hook
  if (this.hooks.beforeTransform) {
    await this.hooks.beforeTransform(ctx, params, doc);
  }

  //  Do transforming

  // Call afterTransform hook
  if (this.hooks.afterTransform) {
    await this.hooks.afterTransform(ctx, params, doc);
  }
}

Motivation

Detailed design

Drawbacks

Alternatives

Adoption strategy

Unresolved questions

Start by reading the linked Action Hooks documentation and tracing the ActionHook middleware, then inspect how custom functions are implemented in moleculer-db. The examples identify transform and populate as target functions, but the detailed design and unresolved questions are empty. Done would require an agreed design and implementation scope for custom hooks.