support Parse Relation

[WahdanZ]

support relation object one to many and many to many
https://docs.parseplatform.org/rest/guide/#relations
http://docs.parseplatform.org/android/guide/#relational-data

[RodrigoSMarques]

@WahdanZ
queries and create with one to many (Pointer): yes.
See section Relational queries or ** Objects** in README.MD

queries and create with Many to many: No
I started to implement, but as I have never used I did not understand the concept

[WahdanZ]

not queries but I'm talking about creating a relation between object

// let’s say we have a few objects representing Author objects
ParseObject authorOne =
ParseObject authorTwo =
ParseObject authorThree =

// now we create a book object
ParseObject book = new ParseObject("Book");

// now let’s associate the authors with the book
// remember, we created a "authors" relation on Book
ParseRelation<ParseObject> relation = book.getRelation("authors");
relation.add(authorOne);
relation.add(authorTwo);
relation.add(authorThree);

// now save the book object
book.saveInBackground();

thre is a ParseRelation object.

ParseUser user = ParseUser.getCurrentUser();
ParseRelation<ParseObject> relation = user.getRelation("likes");
relation.add(post);
user.saveInBackground();

http://docs.parseplatform.org/android/guide/#using-parse-relations

[WahdanZ]

three is different between pointer and relation
A Relation is for when you want a long list of related classes, where an array doesn't work, or when you want to query the related objects as needed and not have the list included every time you load the containing object.

Basically you have 4 options with Parse:

Pointer - single reference to another class (1 to 0..1)
Array - collection of pointers, loaded with the object every time (1 to 0..n, small lists)
Relation - collection of pointers, like a join table in SQL (handled under the covers for you), you must run a query against it to load values (1 to 0..n)
Custom join class - really just another object (like many-to-many join in SQL) with a Pointer to each side plus any related information (1..n to 1..n)

[WahdanZ]

like facebook post the author will be a pointer for the post owner, but likes will be a relation object of the users who like this post

[RodrigoSMarques]

See example below:
The user field that is a relationship with ParseUser (Pointer)
The users field is a list of ParseUsers. (List of Pointers).

Was this?

  final ParseUser user = await ParseUser.currentUser() as ParseUser;
  var parseObject = ParseObject("TestAPI");
  parseObject.set<ParseUser>("user", user);
  parseObject.set<List<ParseUser>>("users", [user, user]);
 ParseResponse apiResponse = await parseObject.save();

Users field content:

[
  {
    "__type": "Pointer",
    "className": "_User",
    "objectId": "0C6ptX39c8"
  },
  {
    "__type": "Pointer",
    "className": "_User",
    "objectId": "0C6ptX39c8"
  }
]

[WahdanZ]

it's different between pointer and relation, If the array of pointer likely to be more than 100 (recommended limit by Parse), it is better you go with relations. Because arrays don't scale to large relationships.

https://www.youtube.com/watch?v=x70G_LPlW60

see the implementation of ParseRelation

[RodrigoSMarques]

I understood. Today lib does not support this.
I started to query, but I did not go any further.

[zenz]

I also encountered the same problem when trying this plugin. I have to modify parse class structure currently.
Hope the related function can be available soon.

[yulingtianxia]

@WahdanZ I had add ParseRelation on branch release/1.0.22

[zenz]

@yulingtianxia it's reversed back to 1.0.21. there's no 1.0.22 release yet.
And, could you please provide some samples how to use the relation API?

[yulingtianxia]

@zenz https://github.com/phillwiggins/flutter_parse_sdk/blob/release/1.0.22/README.md
There is an example in README.md

[zenz]

I gave it a try. and it seems broken something.
My test app can run with 1.0.21 without error. but after switch to 1.0.22, it will bring me this error:
E/flutter (12539): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The getter 'length' was called on null.

Since 1.0.22 was not released yet, so I use git url to fetch it:

dev_dependencies:
  parse_server_sdk:
    git:
      url: git@github.com:phillwiggins/flutter_parse_sdk.git
      ref: 7b24830d4dda74ed7f3cc9d077d4b305d0a69c59

Here's my sample:
https://github.com/zenz/flutter_parse_sample

[yulingtianxia]

I gave it a try. and it seems broken something.
My test app can run with 1.0.21 without error. but after switch to 1.0.22, it will bring me this error:
E/flutter (12539): [ERROR:flutter/lib/ui/ui_dart_state.cc(148)] Unhandled Exception: NoSuchMethodError: The getter 'length' was called on null.

Since 1.0.22 was not released yet, so I use git url to fetch it:

dev_dependencies:
  parse_server_sdk:
    git:
      url: git@github.com:phillwiggins/flutter_parse_sdk.git
      ref: 7b24830d4dda74ed7f3cc9d077d4b305d0a69c59

Here's my sample:
https://github.com/zenz/flutter_parse_sample

@phillwiggins Hi, this issue(#190 (comment)) can also reappear in his sample.

[zenz]

I had figure out why this issue #190 happened.
verison 1.0.22 need masterKey while do Parse().initialize().
When those functions don't need masterKey permission, please don't ask for it.