Best practice for encrypting model properties

Description / Steps to reproduce / Feature proposal

In my application, I have models with properties that need to be encrypted before saved in the database.
I'm trying to decide what's the best practice to implement that use-case.

Current implementation

What I'm currently doing is set an attribute in the property itself:
encrypted: true

In my repository, I override the relevant methods. e.g. create:

async create(entity: DataObject<MyModel>, options?: AnyObject): Promise<MyModel> {
  for (let propertyName in this.entityClass.definition.properties) {
    if (this.entityClass.definition.properties[propertyName]['encrypted']) {
      entity[propertyName] = encrypted(entity, propertyName)    
    }
  }
  return (await super.create(entity, options));
}

There are a couple of problems with this implementation.

• This method is not generic, as if tomorrow I would like to implement another logic?
• It requires to override a lot of methods in the repository.
• It requires editing per repository meaning that the CLI only covers a small part of the creation process.

Is there any better implementation for this issue?

Acceptance criteria

• A mechanism allowing Repository classes to execute custom code whenever the repository is trying to convert model instance into raw data to be stored and also from the raw data to model instance. This is basically an Operation Hook, and it should be implemented by DefaultCrudRepository. See #2095 (comment) for more details, the code snippet is cross-posted below.

• A section in our documentation (e.g. in Key Concepts >> Repositories) explaining how to use these new mechanism.

• A guide in our documentation showing how can applications implement property encryption/decryption.

Proposed implementation:

class DefaultCrudRepository<T, ID> /*...*/{
  protected async entityToData(entity: DataObject<T>, options?: Options): DataObject<T> {
    // "persist hook" - no-op by default
    return entity;
  }

  protected async dataToEntity(data: DataObject<T>, options?: Options): DataObject<T> {
    // "load hook" - no-op by default
    return this.toEntity(data);
  }

  async create(entity: DataObject<T>, options?: Options): Promise<T> {
    const data = await this.entityToData(entity, options);
    const model = await ensurePromise(this.modelClass.create(data, options));
    const result = await this.dataToEntity(model);
    return result;
  }

  // etc.
}

DefaultCrudRepository から始め、提案で説明されている create path と対応する conversion paths をたどります。entityToData フックと dataToEntity フックの動作を定義し、その後、Key Concepts > Repositories のドキュメントをプロパティの暗号化/復号化ガイドで更新します。完了とは、受け入れ基準が満たされていることを意味します。