Firebase - How to order items? - android

I'm trying to make a very simple list-based android app.
Is there a easy way to order objects and sort them by date?
My goal is to show the last added item on top of the list.
I've already tried with a client-side solution but it's not efficient.
At the moment i'm using this json data model:
{
id:"",
name:"",
body:"",
date:"date here"
}
Does anyone have and idea on how to solve this?

You must must use orderedByChild by the key of the date you'd like to order the children by. You can then observe the Value or ChildAdded event type of this query to retrieve the children in ascending order of date. To have the most recent first, you must reverse the objects manually client-side. Otherwise, you could prepend a - symbol to all the dates and handle it client side.

Related

Filter children by inner list value

According to the previous image
Is it possible to get every child of that matches the value of "11000" in that is inside the array ?
(there might be multiple entries for )
It depends on where you start. From /planes/PaMé7800_..._785/directiones it is definitely possible. But from /planes it is not possible, since you can only query values at a known path under each child.
Essentially your current structure allows you to efficiently find the directiones for each plane, but is does not allow you to efficiently find the planes for a directione. If you want to allow the latter, consider adding an additional data structure for it. For example:
directionesStCPToPlanes
dir11000
PaMé7800_..._785: true
With this additional data structure, you can also look up the inverse relation.
This type of double data storage is quite common and is known as denormalizing the data. For more on this, see:
Many-to-many using Firebase
Many to Many relationship in Firebase
Firebase Query Double Nested

Firebase Query - how to order by a separate field?

I'm working with an Android App that functions as an instant messaging service, and I'm at the point of pulling the message data through into a RecyclerView. I have my Firebase Query object returning all the messages that match the id of the chat that has been loaded, this is done like so:
Query qChatMessages = mDbRefMessages
.orderByChild("messageChat")
.equalTo(mChatId);
So far so good, and this is returning the collection of messages that I expect. The problem is now that, upon passing them to the RecyclerView to be displayed, they come out in the inverse order of how you would typically expect an instant messenger to display, so the messages are actually getting older as you scroll down the chat.
My message nodes in the database all have a messageTimestamp field associated with them, so this is what I would want to sort the data by. The problem is that I don't seem to be able to find a way of ordering the data by any field other than the one that I'm querying on, or getting the results back from Firebase and subsequently ordering them.
Does anyone know how I can work around this, or if there's some Firebase capabilities I'm not aware of?
Thanks in advance,
Mark
The easiest way is to store an extra piece of data in your message nodes which is the epoch time multiplied by -1: this way you can sort on this field and the query will return the right order.
See this post on how to get the epoch time: how to get the number of seconds passed since 1970 for a date value?
However, note that with your current data structure, you will encounter a problem: you will need to sort on this new data (e.g. with .orderByChild("messageCreationTime")) AND filter for a given mChatId (e.g. with equalTo(mChatId)), which is not possible.
So, you would have to re-structure your database (if this is possible) like this:
- messages
- mChatId
- messageUniqueID <- most probably auto-generated by Firebase
- messageTitle: ....
- messageCreationTime: -1525857044
And you would query by:
Query qChatMessages = databaseReference.child("messages").child(mChatId)
.orderByChild("messageCreationTime");

How to search in Firestore using multiple fields of documents for android?

I'm using a Firebase Firestore for android to store data. I tried to search data from documents.
My Firestore structure is:
Collection (Products) - Document (Auto Generated ID) - Field (NumberOfPeople,OfferStartDate,OfferEndDate,OfferPrice,Location)
I wrote query for search data on those fields.
CollectionReference collectionOfProducts = db.collection("Products");
collectionOfProducts
.whereEqualTo("Location", location)
.whereGreaterThanOrEqualTo("OfferPrice", offerPrice)
.whereLessThanOrEqualTo("OfferPrice", offerPrice)
.whereGreaterThanOrEqualTo("OfferStartDate", date)
.whereLessThanOrEqualTo("OfferEndDate", date)
.get()
I want search result like this: An offer which is between start date and end date, where offer price is greater than equal or less than equal on give price range. This query is not working in android studio.
How to do this in firestore firebase?
According to the official documentation regarding Cloud Firestore queries, please note that there some query limitations:
In a compound query, range (<, <=, >, >=) and not equals (!=, not-in) comparisons must all filter on the same field.
So a Query object that contains a call to both methods:
.whereGreaterThanOrEqualTo("OfferStartDate", date)
.whereLessThanOrEqualTo("OfferEndDate", date)
Is actually not possible, as "OfferStartDate" and "OfferEndDate" are different properties.
The best solution I can think of is to use only one of these method calls and do the other filtering on the client.
Another possible solution might be to use denormalization and duplicate the data
in certain intervals. In this way, you'll always know the time periods and you'll be able to create the corresponding queries.
To the best of my knowledge, Firestore only lets you use where<Greater/Less>ThanOrEqualTo() and where<Greater/Less>Than() a single field and all other filter operations on other fields can only be whereEqualTo().
Some workarounds for your specific case include -
1) Modifying your query to
collectionOfProducts
.whereGreaterThanOrEqualTo("OfferStartDate", date)
.whereEqualTo("Location", location)
.get()
And then performing the subsequent filtering on the result in your app code.
Alternately, you can perform your filter on "OfferPrice" and "Location" in your query and the remaining filters can be applied to the query result.
2) You can use firebase functions or other server code to write logic that performs customized filtering and fetch the result that way.
i was having same issue with this, but i found a work around that takes sometime to write.
lets say you want to search for a particular keyword(in this case the value of a field inside a document), and you want firebase to search multiple field instead of just looking for 1 particular field.
this is what you want to do.
const searchTerm = document.createElement('input')
db.collection('collection').where('field1', '==', `${searchTerm.value}`)
.get()
.then((snapshot) => {
if(snapshot.size === '0'){
db.collection('collection').where('field2', '==', `${searchTerm.value}`)
.get()
.then((snapshot) => {
if(snapshot.size === 0) {
db.collection......and repeat
}
})
}
})
in summary, the above code is basically telling js to search for the term again with a different field if the result of the previous query is 0. I know this solution might not be able to work if we have a large quantity of fields. But for folks out there that are working with small number fields, this solution might be able to help.
I really do hope firestore one day would allow such feature, but here is the code it worked fine for me.
the problem I have now is to allow search input to be able to search without have me to complete the word. I do currently have an idea how this would be, but just need some time to put together.

Cloud Function to sort the Firebase Child from inner child

I need to have one problem sorted out. I want a cloud function, where I need to loop through every Posts that has uniqueID and I want to sort those uniqueID's according to the value of TotalReactions. To me more vivid, suppose, the first post has totalReactions = 5, and second one has totalReactions = 6, then I need to have another RealTimeDatabase "PostArranged" which sorts them in descending order, so second post which has Total Reaction would be in first and then follows the one which has lesser TotalReaction...
Here is how my firebase realtime database looks like:
Posts
-L29TD-nsUYRu3wYcCQl
Caption: "First Screenshot"
CurrentUserReaction: "notreacted"
Image: "https://firebasestorage.googleapis.com/v0/b/nep..."
ReactingUser
<user-id>:"1"
<user-id>:"2"
Time: "13:40:54"
TotalReactions: "2"
Unique: "-L29TD-nsUYRu3wYcCQl"
UserPhoto: "https://firebasestorage.googleapis.com/v0/b/nep..."
Username: "Me"
Any help would be appreciated ..
This is not a good way to do what you want to do. In this method the database has to be sorted to another "ArrangedDatabase" every time a reaction is added which will happen in a high frequency. So it will be very expensive to do this with Cloud Functions.
Instead use orderByChild(), orderByKey(), orderByValue() to sort data when you're querying data.
Sorting data - Firebase documentation this show it quite well.
For anyone who want to do this in your RecyclerViewAdapter provided by Firebase, it is easily done... When you pass in those 4 parameters. Do not pass the database Reference, instead, make a new query, and make sure to sort that thing either by OrderByChild(), OrderByValue() or anything you want to order by... i.e.
In my case, I will do something like this:
q = mDatabaseReference.orderByChild("TotalReactions");
and pass q as parameter inside FirebaseAdapter, like this:
FirebaseRecyclerAdapter<Posts,PostViewHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Posts, PostViewHolder>(
Posts.class, R.layout.each_post_layout , PostViewHolder.class, q
) {
.
}

GPS data -> MySQL -> Android sorted ListView

I'm programming an Android app that shows data from MySQL database via ListView with some sorting:
1) Items that are closer to android phone by GPS are shown firstly
If there are 2 or more items with equal distance, second sorting parameter applies - time.
2) Items that are closer in time are showm firstly.
Here is a scheme of the process that I guess to implement:
My idea is to get all needed rows into Array, then make some PHP manipulations with it and then pull sorted Array to the phone.
(as shown on the image above)
So please advice me what will be the proper way?
Maybe there is easier method for this functionality?
Or maybe I should do all the sortings exactly in the Android app when programming ListView, getting only standard "SELECT *" array from the database? Then, is there an opportunity to create a ListView with sorting based on calculated values?

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