eoin-obrien/mongoose-update-if-current

/* eslint-disable no-invalid-this */
import assert from 'assert';

/**
 * Implement optimistic concurrency control using a schema's version key.
 *
 * @param {mongoose.Schema} schema - A Mongoose schema to be plugged into.
 */
export function versionOCCPlugin(schema) {
  if (schema.$implicitlyCreated) {
    // Implicit creation mean that it's an internal model, aka subdocument.
    // In this case, we don't want to add hooks, because methods are not existing and it's not relevant.
    return;
  }
  // Get version key name
  const versionKey = schema.get('versionKey');
  assert(versionKey, 'document schema must have a version key');

  // Add pre-save hook to check version
  schema.pre('save', function(next) {
    // Condition the save on the versions matching
    this.$where = {
      ...this.$where,
      [versionKey]: this[versionKey],
    };

    // Increment the version atomically
    this.increment();

    // Invoke next hook
    next();
  });
}