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Hey everyone welcome back to class.

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Johnny be here with slopes dot com.

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And in this lesson we are going to add our first comments and in the process learn about fire store

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transactions.

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All right.

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So let's get started.

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First thing I want to do is just run this and make sure that our segues are working.

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We haven't tested that yet.

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So we are passing from our main these when we click on a thought.

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We were passing that thought here.

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So just to make sure that is working let's go ahead and print out thought that comment or thought text.

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Are you going to run that and when we click on one of the thoughts we should see printed out to our

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log.

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The thought that we couldn't get someone to click on this one.

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And all right so it looks like that is working.

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Don't give up on your dreams keep sleeping is printed out to our blog.

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And before I forget let's go ahead and fix up our table.

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I don't like these dividers and I know there's something else that we need to fix as well.

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So jumping into our main story board let's hear table you selected and separator should be none.

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And then on the Common to sell selection should be none.

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There we go.

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All right.

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So now back into our comments visi.

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So now that we have we know our Segway is working we have a thought variable here that we can reference.

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So let's talk a little bit about how the architecture for this is going to work.

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Now we know that entire store we have our data organized into collections and documents.

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Collection holds a bunch of documents and each of those documents could have some collections.

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So in this app we have thoughts a collection of thoughts and we have these documents that each of these

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documents can have a subcollection called the commons and inside of that collection we will have more

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documents that represent the comments that are added for that particular thought.

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OK so that's kind of how it's going to work.

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So first off let's go ahead and create a reference to the individual thought that is clicked on.

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So here I'm going to say who are thought ref and this is going to be of type document.

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Let's see here.

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Oh I don't think we have fire so that's why.

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So wasn't complaining because we don't have fires firebase imported yet.

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There we go document reference and implicitly and unwrap that and then here in view to load and when

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to say thought ref is equal to fire store.

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And actually we can create a reference for fire store so that we don't have to write out fire store

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fire store every time to save fire or is equal to a fire store that fires store.

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And so here thought Refco going to say fires door at the Capitol One their fire store that collection.

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All right.

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This is the reference to the fact that we selected.

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So looking at our database there would be the reference to one of these individual documents here.

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OK.

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So if I restore the collection the collection path is thoughts ref and then the document path is thought

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that document ID.

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So now we have a reference to the path to the thought that we can use throughout the rest of this class.

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Next thing I want to do in preparation is create a variable for a username Katulis a variable user name.

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And this is going to be a string and where we're going to get this is from our off.

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So if you remember a couple of lessons ago in our create user Visi we actually set a display name that

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we can access from our user.

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So here comments VC I'm going to say there's going to be an option or someone to say if that name is

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equal to off that off that current user.

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OK so this gets the cached current user or gnoll if there is none.

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OK so the current user.

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And then we access the display name and then we're going to say a user name is equal to name.

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Very good.

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All right so now let's get to our ad comment tapped button.

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OK so this is what it is called When we look to add a new comment.

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And so first up let's go ahead and get our comment tecs.

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So when we say God let comment text equal self-taught.

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I don't mean this right here and say what did we call it we called it add comment text.

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So add common text that text else return in case and now we have the text of the comment that we are

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adding in this bottom pane here.

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All right so now we are ready to add our comment.

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So previously we just use the firestorm method and document which has a completion handler where we

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add the data as a dictionary and then send it up.

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Right.

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And we could do that.

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But the reason that we're going to use something else which I'll explain here in a second is that we

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are also wanting to update the number of comments for this thought in our fire store database.

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So we're adding a document but we also need to be adding incrementing a value in the thought document

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as well.

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And so we would be doing multiple reads and writes and that's actually best handled in something called

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a transaction.

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OK so when a transaction you can group multiple operations into a single transaction transaction consists

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of any number of get operations followed by any number of right operations such as set update or delete.

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All right so why do we need a transaction here.

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Well just like I said we're going to be adding a comment as well as updating the field the value for

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the thought.

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But a couple of things to keep in mind.

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For a transaction I read operations must come before right operations.

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So first we're going to read from the thought we're going to get the number of comments that it currently

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has.

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And then we are going to update that field as well as add the new comment for it.

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Rule number two transactions never apply partial rights.

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So it's an all or nothing deal and transactions fail when user is off line.

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So that's something to keep in mind and a transaction should not directly modify the application state

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meaning that this transaction is not executed on the main thread.

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With that all out of the way let's go ahead and code it up.

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So to do so we just call fire store that run transaction and press return and we have a handler here

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and we have a transaction and then error pointer.

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And then here in the code and then we have another question handler here.

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And this is we're just going to call this object and error in code.

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OK so this transaction is what we're going to be working with here inside of the actual running of the

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transaction.

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And then here is an object that could be returned out of the transaction.

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OK.

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So go ahead and just say return nil.

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We're not going to be returning anything out of the transaction.

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All right so remember that reads need to occur before rights.

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So first we're going to get the thought document so that we can know how many number of comments there

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are so that we can add one to it when we add this comment.

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OK.

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So I'm going to create a thought document here type document snapshot and I need to declare it here

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because we access it in a try block which I'll write out here.

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OK.

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So you can try her catch catch well-led error as in this error and then return nil.

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And then now we're going to say Try thought document and my auto correct gets a little bit funky here

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for some reason every time.

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So just follow along closely so thought document is equal to trend's action dot net document.

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And then we put in the path to the document which is a fire store and fire store

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that going to drop this down to a new line.

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That collection of thoughts underscore rough and I need a dot right here collection dot document.

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And finally auto complete is back so there we go that document and the document is or the path is self-taught

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thought that document Heidi.

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All right so a little bit harrowing there for a minute.

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I'm not sure why the autocomplete gets all freaky inside of this transaction but just to recap we say

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lead thoughts document equal a document snapshot and then we try to get it from transaction dot document.

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And then we pass in the path to it.

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And then here we're just going to debug.

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Print the error if there is one.

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When I say Fetch ever and we're going to string interpolate the error dobbed localized description.

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All right.

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So now we have the thought document.

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So what do we need out of it.

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We need to know how many likes it currently has.

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So we're going to say guard that old gnome likes people and we're going to access the thought document

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fact document that data.

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So we're going to get the data from it which is a dictionary and we're just going to grab it out of

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that dictionary of the number of comments and we're going to cast this as an else returned and I just

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realized that I said likes here this should be comments so old mom Common's is equal to thought document

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data the number of comments cast it doesn't else return.

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So basically all we're doing is what we have here but I need to return now.

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There we go.

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Basically all we're doing here is we're just drilling down from our thoughts to the document to the

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number of comments and extracting that data and then we can just see transaction that update

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data and the fields is numb underscore comments and the value is old comments plus one and forward document

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the document reference is sulf that thot ref.

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All right so now we have taken care of updating the number of comments for the thought that we have

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clicked on when we add a comment.

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All right next thing we need to do is actually add the comment.

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OK.

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So let's go and do that now.

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In the past we have always used the audio generating document IDs.

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However when you use set which you have to use in a transaction you have to explicitly set the ID and

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so the workaround for that is to create an empty document first which uses the auto generating ID and

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then using that.

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All right.

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So we're going to say let new comment ref equal self dot fire

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store data collection and the collection path is thoughts ref.

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Then we drill down one layer deeper to the document and that is at self-taught thought that document

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ID and then we go one layer deeper to a new collection called the comments.

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And let's go ahead and create a constant for this.

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So I'm going to jump back and we're Constans file.

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And here with our other references I'm going to say let comments ref equal comments.

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Copy this gem back in the comments AVC and set the collection are to comments and then we just say document

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that just kind of creates an empty document.

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Now when we create our new comment document and we'll we'll pass this comment in the common ref.

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OK.

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So we're going to see transaction data set data and that's the one we want here for document.

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The document here is the new comment ref.

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And here the data that we're going to pass in is we're going to do the user name the timestamp and the

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comment text.

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So I'm going to say comment text and that is of value right here.

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Comment text comma.

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Then we're going to use the username or the time and this is a concept that we already have and that

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is field value that server time stamp.

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And then another common comma and the third value that we were adding to our comment is the user name.

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So when I say user name and that is also user name and I can hear the self here.

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Since we're inside of a closure and then this can turn this into a constant here.

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So we're going to copy that as well and come into our Constans file here and here with the rest of the

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field contents.

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I'll say let comment underscore the extreme equal comment text and then I'll copy this constant here

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jump back into comments Visi and replace that save that save our Constans file and back in the comments

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visi.

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I think that looks good.

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So now let's handle if there is an error.

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We'll just say if left error is equal to error we are just going to debug printed something to say debug

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print and it's going to say transaction failed and print out the error.

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Else if it was successful then we're just going to clear out the comment text field so that it's ready

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for a new comment.

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I going to say self that enter or add comment text that text is equal to an empty string.

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All right so that looks good.

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Let's go and just review real quick what we did.

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All right so when someone clicks on the Add comment button what we do is we run a transaction.

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And the reason we use transactions is when you have multiple read and writes all right.

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And so with a transaction we have to read it first and so we did that here.

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We do have a do catch block where we try to read from the database.

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Our thought documents we say get document and then we pass in the path to the thought document.

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If something goes wrong then we print it out and then from there from that document that we read we

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get to the number of comments data since that's what we want to increment by one.

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And as we get that information and then we update that data using the number of comments field and incrementing

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it by one and then finally we actually get to the part where we are adding the new document and to do

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that we first create a new comment a ref so that we can have an auto generated ID and we create the

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new comment here by saying set data and we pass in the data that we want to create and set in our new

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document and that is the common text timestamp username and then finally we handle the error if there

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is one.

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So let's go ahead and test this out.

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I'm going to run it all right so I'm going to click on the serious one from Aristotle and I'm going

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to write here.

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Gonna go ahead and add a comment.

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So keep in mind that right now we don't have the capability to.

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If we wait if we toggle our keyboard here.

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So if you come down a hardware keyboard and if you toggle the software keyboard that's going to cover

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it up.

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So just keep that keyboard on toggled for now.

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We might get to fixing that later.

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So when I added comments to say adding first comment when I pressed the button and it cleared.

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So let's go ahead and check our.

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And we don't get any error statements here so it's good to check our database and find that one.

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Let's see here.

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Here it is.

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So now we can see this is the one that we commented on and it has a subcollection of comments and if

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we click on it then we have documents and if we click on that document there it is adding first comment

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right so that is pretty cool.

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That's going to add a second one simulator and get a second hand added.

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And here we can see that it was added right here.

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All right.

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Very cool.

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All right so now we have learned all about transactions and how we can work with multiple read and writes

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at once.

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And yes now we are adding comments in the next lesson or we are going to work on pulling them down from

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this subcollection and displaying them all right.

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So I'll see you then.