How to use Relation fields in parse.com

问题

I'm using parse.com, and I just want to know how to set and get relational data in a ParseObject Subclass, for example like this.

Can you please give an example of field of type Relation and show me how to set and get it in the subclass?

Thanks so much in advance !

回答1:

I'm not sure about what you are really asking. Relation fields are sets of pointers to other ParseObject. You don't have to add convenience methods in the subclass if you don't need to. The super class ParseObject has all the methods necessary to interact with relation fields. The main entry point is getRelation("columnName"), which you can use on any ParseObject instance.

Let's say you have a AnywallPost class and you have set a relation column, "likes", storing all ParseUsers that like that post. Documentation is pretty clear in explaining how to get/set.

Set

You don't really set anything, you just add a new item in the relation field.

ParseRelation<ParseUser> relation = anywallPost.getRelation("likes");
relation.add(parseUser1);
relation.add(parseUser2);    
anywallPost.saveInBackground();

A convenient method inside your subclass could be add(ParseUser user):

public void add(ParseUser user) {
    ParseRelation<ParseUser> relation = this.getRelation("likes");
    relation.add(user);
    this.saveInBackground();
}

Then you can simply call anywallPost.add(parseUser).

Get

You don't really get anything, but rather you find items inside the relation. This is honestly well documented in the official docs. A useful method inside your subclass could give you the query:

public ParseQuery<ParseUser> getLikes() {
    return this.getRelation("likes").getQuery();
}

Then you can use ParseQuery<ParseUser> q = anywallPost.getLikes() and use the query as you wish.

来源：https://stackoverflow.com/questions/32056085/how-to-use-relation-fields-in-parse-com

标签

android

parse-platform

relational