Add generator support for FK constraint

[matei-tm]

Is your feature request related to a problem? Please describe.
The M8 framework include annotations for signaling FK on models. The annotation must generate FK constraints

Describe the solution you'd like
Add generator support for FK constraint. The implementation will lead to models supporting fields of type from another model.

[StefanLobbenmeier]

Will this enable FK support like in Hibernate:

@Entity
public class Task {
    @Id @GeneratedValue(strategy = GenerationType.AUTO)
    @Column(name = "task_id")
    private int id;
    @ManyToOne
    @JoinColumn(name = "task_status_id")
    TaskStatus status;
}

[matei-tm]

In f-orm-m8 I proposed to signal Fks at the @DataColumn annotation level in the CompositeConstraint list.
Annotations could be placed on fields of complex types, which in turn will have a representation in the database in dedicated tables. As well, the annotations could be placed on the fields that represent the primary key combination of the entity being referenced.
At the level of implementation, which is the most appropriate approach, should be discussed. If the dependency chain is an aciclic graph (i.e. a tree), the load seems feasible. The problem arises when we encounter cyclic dependencies, involving a lot of tests, validations and eternal questioning who was the first "egg or chicken."
As you mentioned well, an extra set of annotations is likely to be needed.

[StefanLobbenmeier]

Sorry for the late response. I am a bit confused when you talk about the database as an cyclic graph. From my understanding, an ORM will only provide "one hop", using foreign keys to connect 2 tables.

[matei-tm]

Looking to the generation workflow, the database is on the output side of stream. The input is a collection of models. The engine must parse each field of a model and extract the needed information to write a proper proxy and the database provider methods (table creation, entity CRUD).
When I am speaking of dependency chain, I am thinking to the model fields that are of another model type. The FK come in to scene when we need to implement one-to-many and many-to-many relationships. For example, a trivial one-to-many case, seems easy to handle:

class ModelA {
  int id;
  ModelB sampleField;
}

class ModelB {
  int id; 
}

The troubles are coming to scene when we try to inspect the following case, which involve a cyclic graph:

class ParentModel {
  int id;
  ChildModel childField;
}

class ChildModel {
  int id; 
  ParentModel parent;
}

And the list may continue....

[TheDevelolper]

I have the need to store products and allergens. Is this possible using the ORM?

So one product may contain many allergens.

Here's what my models look like:

import 'package:f_orm_m8/f_orm_m8.dart';

@DataTable("product_db_models")
class Product implements DbEntity {
  @DataColumn("id", metadataLevel: ColumnMetadata.primaryKey)
  @override
  int id;
  @DataColumn("name")
  final String name;
  @DataColumn("description")
  final String description;
  @DataColumn("price")
  final double price;
  @DataColumn("imagePath")
  final String imagePath;
  @DataColumn("hasOptions")
  final bool hasOptions;

  @DataColumn("allergens")
  List<int> productAllergens;

  Product(this.name, this.description, this.price, this.imagePath,
      this.hasOptions, this.productAllergens, this.id);
}

import 'package:f_orm_m8/annotation/column_metadata.dart';
import 'package:f_orm_m8/annotation/data_column.dart';
import 'package:f_orm_m8/f_orm_m8.dart';

@DataTable("product_db_allergens")
class Allergen implements DbEntity {
  @DataColumn("id",
      metadataLevel: ColumnMetadata.primaryKey | ColumnMetadata.autoIncrement)
  @override
  int id;

  @DataColumn("name")
  String name;

  Allergen(this.name);
}

When I try to implement a list in this framework I get the following in product.g.m8.dart:

// GENERATED CODE - DO NOT MODIFY BY HAND
// Emitted on: 2020-06-07 10:02:25.307599

// **************************************************************************
// Generator: OrmM8GeneratorForAnnotation
// **************************************************************************

/*
Not all the models have passed the validation process. Review the following issues, fix them and rerun the builder:

Error: The type List of Product.productAllergens is not implemented. Remove it from the model.
*/

[StefanLobbenmeier]

  @DataColumn("allergens")
  List<int> productAllergens;

Change the type from int to Allergen

  @DataColumn("allergens")
  List<Allergen> productAllergens;

[TheDevelolper]

Sorry yeah I tried that too but I had the same problem

…

On Sun, 7 Jun 2020, 10:48 Stefan Lobbenmeier, ***@***.***> wrote: @DataColumn("allergens") List<int> productAllergens; Change the type from int to Allergen @DataColumn("allergens") List<Allergen> productAllergens; — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#96 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AA6XBOOFYPR374UXF4GIX6LRVNPAHANCNFSM4HNMSZGA> .

[StefanLobbenmeier]

Oh my bad it’s been a while since I looked into this project. I guess this ORM leaves relationships to implement for the user. (This was also what my original question was about).

In your case you have a n:m relationship so you will need an additional table “ProductAllergens” with the fields Product and Allergen.

[TheDevelolper]

Ah I see, I'd need a class to represent the Tuple / Mapping table