Develop Reference

Complex Parse Query in Android

I have these Classes in parse db.
User ...
Post (user pointer<_User> | images Relation )
Image (post pointer | image File )
Follow ( user_from pointer | user_to pointer)
The questions are,
1- How to get the list of posts with their images of users who i am following. (in java android)
2- How to get a list of my posts.
3- How o get a list of my followers.
4- example of java class of User, Post, Image and Follow objects.
thanks

probably you'll need to construct a relational queries, like the example below:
ParseQuery<ParseObject> innerQuery = ParseQuery.getQuery("Post");
innerQuery.whereExists("image");
ParseQuery<ParseObject> query = ParseQuery.getQuery("_User");
query.whereEqualTo("postPointer", innerQuery);
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> commentList, ParseException e) {
// comments now contains the comments for posts without images.
}
});
You can check more about it at Parse Docs

Parse Relation Query:How to Get Only one user from relation list

Hi there I'm new to parse, android and stackoverflow.com, here is my question
I've two classes on parse one is "post" and other is "user" class. Anyone can like post and dislike post.
I've created two relation column "whoLiked" and "whoDisliked" which points the list of users who has liked/disliked a specific post.
When I'm showing the post to the user I want the current User to like/dislike the post Only once which I've set properly.
But only thing I'm not getting is how can I fetch only currentuser from thisPost object.
I don't wanna fetch the list of user who liked this post I just want to know if current User has liked it or not.?
I'm new to stackoverflow.com plz ignore if any mistakes here. Thanks u all in advance.
Below is the query to fetch all the liker
ParseObject post = ...
// create a relation based on the authors key
ParseRelation relation = book.getRelation("whoLiked");
// generate a query based on that relation
ParseQuery query = relation.getQuery();
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> comments, ParseException e) {
if (e == null) {
// "user" is now a list of the user who liked
} else {
// Something went wrong...
}
}
});

Just add a constraint to check if the objectId is the same as the currentUsers's objectId:
// create a relation based on the authors key
ParseRelation relation = book.getRelation("whoLiked");
// generate a query based on that relation
ParseQuery query = relation.getQuery();
// ADD CONSTRAINT HERE:
ParseUser currentUser = ParseUser.getCurrentUser();
query.whereEqualTo("objectId", currentUser.getObjectId());
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> comments, ParseException e) {
if (e == null) {
// "user" is now a list of the user who liked
} else {
// Something went wrong...
}
}
});

Find all following users where their username begins with myString

These are the columns of my Follow Table:
user (Pointer _User)
follower (Pointer _User)
What I want to do is to get all the user where
follower = currentUser
user.username begins with a certain string
I know that in lower-lever db (like mySQL) these data can all be fetched with a single query.
Is it possible in parse? If not, what's the best way to do such a thing?

Assuming your currentUser object is a PFUser
Note... I am program with parse in objective-c so I am not 100% sure this will run. But I feel like this is what your looking for... Your going to have to first query for all the followers who's follower field is equal to the current user.
Then join that query with a user query whose usernames or names, whatever, are equal to your string you pass in... beware the string you pass into the query is case-sensitive... i think...
So if a user in your app searches for BOB and the database has Bob stored... the query won't return Bob... It will just return nothing....
ParseQuery<ParseUser> userQuery = ParseUser.getQuery();
userQuery.whereEqualTo("username", certainString);
ParseQuery<ParseObject> followerQuery = ParseQuery.getQuery("Followers");
followerQuery.whereEqualTo("follower", ParseUser.getCurrentUser());
followerQuery.matchesKeyInQuery("user", "follower", userQuery);
userQuery.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> list, ParseException e) {
// comments now contains the comments for posts with images.
}
});
EDIT Going through Parse's Anypic project that does what you want... I feel that this is not possible... Your going to have to first make a query for the users in the followers table whose followers key is the current user. Then find the objects. Once the result is returned, iterate through the objects to whose names is contained within the contains string.
ParseQuery<ParseObject> followerQuery = ParseQuery.getQuery("Followers");
followerQuery.whereEqualTo("username", certainString);
followerQuery.whereNotEqualTo("username", ParseUser.getCurrentUser().username);
followerQuery.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> list, ParseException e) {
for (ParseObject element : list) {
if (element.user == ParseUser.getCurrentUser()) {
//This is a follower of the current user... append to a list object or whatever
}
}
// update a label or table once the iteration is done.
}
});
There still may be a solid solution for what you want to do in one query but I can't think of it right now... Ill come back to this post if I do.

Query last rows from parse.com table?

I am trying to query last 20 rows from my Parse.com table. I have followed tutorial and generated the code below. The code is returning 20 rows from the table but not last 20 rows. I returns first 20 items. How to retrieve only last 20 rows?
ParseQuery<ParseObject> query = ParseQuery.getQuery("Activities");
query.setLimit(20);
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> scoreList, ParseException e) {
}
});

It seems you would only need a different sort method on the ParseQuery you are making. You can order the query results by the CreatedDate field:
// Sorts the results in descending order by the Created Date field
query.orderByDescending("dateCreated");
So, in your code, it would be something like:
//Where "CreatedDate", set the name of the Created Date field in your table.
ParseQuery<ParseObject> query = ParseQuery.getQuery("Activities");
query.orderByDescending("CreatedDate").setLimit(20);
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> scoreList, ParseException e) {
}
});
In the end, you get also the first 20 results, but the results are ordered the other way around, so that should work as intended.

I had the challenge to order ascending but want to get the last record anyhow.
The solution is simple:
query.ascending("your col");
query.find({
success: function(result){
var lastRow = (result.length) - 1;
var highestValue = result[lastRow].get("your col");
}, error: function //... and so on
Sometimes you don't want to order descending ...
Hope I could give something back to this great forum which helps me a lot!!

Relation query in Parse.com

This is a basic question, but I can't understand how the relationship works in Parse.
I have this relationship: Image link
Briefly, it is a relationship 1 - N. One FeedPost have several comments.
I wish I can send the post ID in the Query and just get the araylist of comments on that post.
ParseQuery<ParseObject> innerQuery = ParseQuery.getQuery("Comments");
innerQuery.whereExists("UXKFwWyn3l"); //ID of the post
ParseQuery<ParseObject> query = ParseQuery.getQuery("FeedPost");
query.whereMatchesQuery("objectId", innerQuery);
Anyone can help me?

With this line
innerQuery.whereExists("UXKFwWyn3l");
you are saying "all records that have a value in the column 'UXKFwWyn3l'"
Also, you are using PFRelation when you should rather use pointers. In Comment, you should have a column with a pointer to the FeedPost. If you did, this query would get you the comments you want, providing you have the FeedPost object already:
ParseQuery<ParseObject> query = ParseQuery.getQuery("Comments");
query.whereEqualTo("post", thePostObject );
query.findInBackground(new FindCallback<ParseObject>() {
public void done(List<ParseObject> comments, ParseException e) {
if (e == null) {
// "comments" is now a list of the comments
} else {
// Something went wrong...
}
}
});
You can also have a reverse relationship in FeedPost, which should be an array of pointers to the comments (not a PFRelation). If you do, you can get both the FeedPost and the comments with one query:
ParseQuery<ParseObject> query = ParseQuery.getQuery("FeedPost");
query.include("comments"); // this is the column with an array of pointers to comments
query.getInBackground("UXKFwWyn3l", new GetCallback<ParseObject>() {
public void done(ParseObject feedPost, ParseException e) {
if (e == null) {
// Your feedPost now has an array with all the comments
} else {
// something went wrong
}
}
});
You should only use PFRelation for advanced relations (like many-to-many).