Add support for embedded objects

[marcosmko]

Implementation for @Embed annotation based on #328 by @hsul4n.

In this approach, you declare an Embed class exactly like you declare an Entity, with support for ColumnInfo annotation too.

@Embed()
class Timestamp {
  @ColumnInfo(name: 'created_at')
  final DateTime createdAt;

  @ColumnInfo(name: 'updated_at')
  final DateTime updatedAt;

  Timestamp({required this.createdAt, required this.updatedAt});
}

When declaring your FloorDatabase, you pass to @Database annotation the classes that are for embedding in other entities (I also added TypeConverter for DateTime).

@TypeConverters([DateTimeConverter])
@Database(version: 1, entities: [Task], embeds: [Timestamp])
abstract class FlutterDatabase extends FloorDatabase {
  TaskDao get taskDao;
}

And finally, you add the Embed type to your Entity.

@Entity
class  Task {
  @PrimaryKey(autoGenerate: true)
  final int? id;

  final String message;

  // @ColumnInfo(name: '')
  final Timestamp timestamp;

  Task(this.id, this.message, this.timestamp);
}

Note that I added the possibility for naming the embed type. If you do not declare a name, it will use the field name as a prefix. If you declare an empty name, then it will embed the Timestamp fields directly.

For example, in the provided example it will generate timestamp_created_at and timestamp_updated_at columns, while if you provide an empty name it will generate created_at and updated_at columns.

Closing #9

[marcosmko]

Hello @vitusortner and @mqus , I re-made this feature using a better approach for declaring embedded classes.

There are still some problems like creating the column name, but I would like to request a first review for validating this approach.

[marcosmko]

@vitusortner Updated PR description explaining how to use this feature.

[marcosmko]

delete

[marcosmko]

switch message error

[mqus]

Thank you for taking the time to implement this!

I really like that you take the road of the type converters, this seems to fit in well, as type converters basically do the same thing (modulo converting one to many attributes and being able to set converters more precise). But for the API surface I rather like rooms approach more (see the comments). This is just a rough review though and @vitusortner surely also has some opinions :D

I enabled the CI pipeline, just ask if you want to know something :)

I'm curious to hear your opinions.

[mqus]

Do we need to include the embeds here? doesn't it suffice to annotate the usage in the entities/views?

[marcosmko]

We need to include if we annotate the embedded class, if we annotate the variable like room then we don't need to include here.

[mqus]

I'm personally in favor of having @embedded here, like in room to be able to more finely adjust where to embed and where to type convert... what are your opinions here?

[marcosmko]

Hello sir!

I don't have a background in Android/Java so I was not aware of the room approach.

I think that annotating the class as an embedded type is easier as we need to annotate it just once, instead of annotating every time we declare it inside an entity class. For finely adjusting, as we have just the prefix string, I thought we could use the ColumnInfo name as we already do for other variables.

If you prefer the room approach I can modify it, just tell me :)

[marcosmko]

Hello, any news here?

[Johann673]

Very nice feature, thank you @marcosmko for the job !

I have one suggestion :
It can be very nice if the Emeded object in entity can be nullable.

For exemple :

@entity
class Crew {
  @primaryKey
  final int id;

  @ColumnInfo(name: 'employee')
  final Employee? employee; // Employee can be null, so "employee_id" is nullable and also "employee_name"

  Crew({
    required this.id,
    this.employee
  });
}

@embed
class Employee {
  final int id;
  final String name;

  Employee({required this.id, required this.name});
}

Thanks you !

[marcosmko]

Hello @Johann673 , actually I'm still waiting for the project owner to review this PR so I could make improvements... 😅

[DesmondFox]

Looks great but why still don't reviewed? 🤔

[mataide]

What is missing?

[mataide]

@marcosmko An embed class can't be an Entity also?

[DesmondFox]

Why is it not merged? I just need this feature

[marcosmko]

Waiting for code review, guys :/

[DesmondFox]

a lot of time has passed. Didn't the owner have time to review?
@vitusortner

[Kraigo]

What's progress for this feature?

[dkaera]

What's progress for this feature?

Currently it postponed for a while. The MR is so far from the actual develop, so it needs to review again and update.

[Velkamhell97]

Any update ?