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In the previous videos we wrote a very simple app that created a database and inserted some data into

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a Contacts table.

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In this video I'm going to show you a little bit about the Android File System.

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This can be useful so that we can check where our database file is,

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then we'll open it and have a look at the data in there.

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So Android is built on Linux. Android and Linux uses forward slashes rather than back slashes in paths.

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File and Directory names are case sensitive:

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so in other words /data is not the same as /Data with a capital D. Now Android

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creates a new user account for each app, to keep each app secure. App data is stored under the package

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name in /data/data, and Android emulators are rooted,

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and I'll talk more about rooted shortly. The Android operating system is based on Linux.

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That's right.

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Essentially an Android device is really a Linux system.

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So if you've already been using Linux, or used Linux, then you'll be already very familiar with

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the file system and the basic commands we're going to look at. 0S X on a Mac also shares a lot in common with

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Linux, as both operating systems evolved from Unix.

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Now if you're used to Windows on the other hand, remember that Linux uses the slash character in file

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paths, the forward slash, rather than the back slash used by Windows.

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And again as I mentioned, Android installs and runs each app under a separate user account, and it creates

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a new account for every app that's installed. By default,

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Linux doesn't allow users to access each other's data,

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so this results in a great deal of security.

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One app can't access the data belonging to another app, and that includes our database.

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Now there are ways to share data, and we will be looking at that later in this section.

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Now an app data is stored in a sub directory inside /data/data, and each app has

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its own directory in there.

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The app's directory name is just the package name, and we'll look at that shortly.

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Now finally some of the emulators are rooted, and what that means - it doesn't mean that they're not

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working - it means that you've got root access, or administrator access

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if you prefer the Windows term, so you can access everything on the device. But unless you've rooted your

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physical phone, much of what we're about to do here won't work on a physical Android device.

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And the other thing to note is that it won't work on the Google Play emulators. I mentioned way back

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in Section 3 that the Google Play emulators don't allow root access.

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You can either have the ability to install apps from the Play Store with your emulators, or you can have root

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access to the emulator.

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You can't have both - at least not at the time I'm recording this video anyway.

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So what that means is that it's important not to use a Google Play emulator if you want to examine your

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apps database on the emulator. Now the Google APIs

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emulators are fine.

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Make sure you choose an image that doesn't have an entry in the Play Store column in the AVD manager.

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And what I mean by that, so I'm just going to open the AVD manager up, and you can see over here we've got a Nexus 5X API 26, and

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we can update that in a few videos time.

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But notice we've got the little Play Store icon.

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So that's an example of a device that isn't rooted.

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So in other words we wouldn't be able to access the database.

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But this one down here, and I've actually made it clear that it has got root access, noting that it hasn't got

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the Google Play icon there.

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And you can see over here it says Google APIs. So we're able,

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we've got full access to that, root access to that,

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and in fact that's the emulator I've got running at the moment.

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And you can see up here, the difference there is it's got Google Play.

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So bottom line here is if you want to follow along

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in this video and get access to the database from the command line,

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you'll need to make sure you're not running an emulator that has been set up with Google Play.

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OK.

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OK, so I'm back in Android Studio with the sqlite project loaded, and I've started the emulator that I was testing it on.

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You can see over here if I tab over to it. There's our sqlitetest app running.

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So what I'll do is I'll just run it one more time, just to make sure we're all on the same page and it's

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still working. I'll open up logcat, and we'll just show the emulator on the screen. And you can see we've got our data there,

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our two records coming back, and we've now got it showing with the record ID as

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Number 2 as well, as id 2.

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And by the way when you run an app on your emulator, Android studio installs it just like any app that you

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download on your phone.

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So what we're about to see applies to all Android apps.

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So we're going to open the terminal window - close this one first,

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the logcat. Open the terminal window

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down here by clicking on Terminal. And what I'm going to do is put that into Floating Mode, just so I can move this up here out

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of the way a bit and resize it a little bit, so it won't affect any subtitles if you happen to be running that.

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So you can see that you've got a fair bit of flexibility in how you organize these panes when you're working

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with them. Alright, so now about the command line. To check that there's a device available we use the command adb devices,

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adb devices. Press enter, and you can see there's a list of devices attached. So that command returns

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a list of devices attached.

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And you can see here that I've got an emulator connected, noting that an emulator just appears

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just as a physical device would,

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as far as the adb command is concerned. Now because I've only got the one device connected, I can type

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adb shell, and we get a prompt on the device now

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so I've gone into the emulator. Now on Linux the command to show a directory listing

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is ls, which is the equivalent of dir on windows.

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It'll give us a bit more information on each file, so I'm going to do ls space -l lower case. There's

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a list of files -

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this is on the actual emulator now.

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So even though we're effectively running with root access on the emulator, we still don't have permission

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to the files in the root directory.

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We still haven't got full access to everything, and we're not seeing a permission denied error, but basically there'll

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be some files that we won't be able to access until we give ourselves that full access.

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Now some emulators such as the Microsoft one will give you more permissions, so you might not get a

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permission denied message there. We know that Google changes things a bit

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so you may not see it with the Google emulators either.

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But you can see here that the bottom line is I haven't got that permission denied.

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But it's not a problem though because on an emulator, what we can do is request super user access.

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So I'm going to do that.

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Type su, that's the super user access, and do an ls space -l again. And it's very unlikely that you'd be able to

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use the su command on a physical device. Even if you've rooted the device, you still need to get the program that

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actually runs the su command onto it yourself.

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Alright, so now that we can see the file and directory names, the one we're interested in is the directory called

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data. Now on Linux, a d in the first position of that sequence of characters - we'll just have a look at that -

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d over here, this first sequence of characters, that indicates that it's a directory.

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If there's an l there that means we're looking at a symlink,

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sort of like a shortcut to another directory.

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So looking at etc for example,

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notice that that's got an l, and it's actually redirected to slash system slash

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etc as you can see over the right hand side there.

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So basically etc here,

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the folder etc, is a shortcut to the folder /system/etc.

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Now we're not really interested in most of the files and directories here.

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So let's have a look into that data directory.

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So I'm going to type cd space data, then I'm going to type ls space -l. And by the way, notice down

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the bottom that the prompt is changing to show the current directory. So we can see now that we've changed

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to the data directory - this is the prompt down here. Once again most of the stuff isn't relevant to what we're

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doing at the moment,

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but you can see how he can use change directory command cd to change into different directories.

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Alright, so let's change into the data directory again.

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So this will effectively be the data slash data directory.

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I'm going to type cd space data again, and notice now that the prompt is showing as data slash data.

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So again the prompt's changing to reflect the directory we're currently in,

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and that's very useful as a check so that you don't do something in the wrong directory. And I'll do an ls space -l

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there now.

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So now that we're in data data, and now things are starting to get a bit more interesting. We can see the storage

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directories now for all the apps listed, or installed rather, on this emulator.

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Now there's quite a few that came with the emulator, and we can also see some of the apps that I tested

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if we scroll up.

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So I'm just going to scroll up and have a look there.

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If you keep scrolling up you notice that we've got the academy.learnprogramming ones. We've got calculator,

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flickerbrowser,

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the sqlitetest, our current app, and also a top10downloader showing there as well.

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But basically every app that's installed has got its own folder for databases.

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So at this point we're interested in our sqlitetest app.

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So referring back to Android Studio briefly - we're scrolling up - notice that, you probably recall that our package

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is academy.learnprogramming.sqlitetest.

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So therefore we need to use that folder - we need to go into that directory and see what's in there.

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So I'm going to type cd space. Now I could type in academy.learnprogramming.sqlitetest, but all I really

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need to do is type in the first few letters,

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aca in this case, and press tab.

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And that gives me a list of all the directories that match what I've typed in so far. So academy

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dot learnprogramming dot, and what I could do now is just type an s, press tab again,

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and we've now got the full path and I can press enter there.

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And we're now, as you can see by the prompt, in academy.learnprogramming.sqlitetest. I'm going to do an ls space -l again.

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Now at this point we're really interested in the databases directory.

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So let's change into that directory and have a look at our database - cd space and type da again for databases

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and a space -l.

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And finally we've got to this place now where our database resides, and you probably remember that file

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name that we chose - sqlite-test-1.db.

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So basically we've found our database file.

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Now notice that in addition to the database file, there's a file with the same name and dash journal

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on the end.

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It's sometimes there, it's usually there, but it may not be there in your case. This dash journal file - this second

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one here -

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that's a transaction log

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that sqlite uses to handle database transactions.

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So it's used if something goes wrong

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and an update can't be completed for any reason.

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So using the transaction log, sqlite can undo all the changes and put the database back into the

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state

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it was in. If all goes well, it uses the journal file to commit the transaction.

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So at this point anyway, we've found our database file and we can see that I'm now looking at the prompt that's

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in the data/data/academy.learnprogramming.sqlite

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test/databases directory.

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So once you know your project's package name, you can find the database easily.

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It'll always be in the same path -

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it's just the package name part that varies.

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Alright, so now we've got to this stage, let's open the database and check that it's as we expect it will

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be.

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So I'm going to type sqlite

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3 space and then sqlite. We've got the same option there and I'm going to type select the db, which is selected

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for us by default, and just press enter there

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now when I press tab, and we're going into the database. So I could've also just typed in the whole

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file name but I typed sqlite,

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s q l and pressed tab, and we matched part of the name enough for it to open up anyway. Alright so that gives

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us the familiar sqlite prompt that we've used earlier in this section of the course, and we can use

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all the commands that we've seen in those earlier videos in this section.

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So firstly let's check the structure of our database, .schema.

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Now that's interesting.

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We've got the contacts table that we expected,

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but there's another table in there called android underscore metadata.

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Now that table's created automatically by the sqlite database class, and it's used for localization

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to allow searching for words that contain accented characters, for example. Now it contains a single field

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called locale with the locale to be used,

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but we don't normally have to worry about that table because Android creates it for us.

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So we're going to ignore that table.

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Instead we're going to have a look at our contacts data.

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So I'm going to type SELECT space * FROM, space * FROM and contacts, and add a semicolon on the end, and there's our

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two records.

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So let's add another one here to check this is all working properly.

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And by the way, if you're unable to run an emulator on your system and you're using a physical device instead,

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don't worry about not being able to perform this next step.

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Your database will have one less row than mine, but you can always modify the app to add the extra row

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if you want.

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So what I'm going to do is add a new record

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using the sqlite command line interface, and then we should be able to see it when we go back

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into our app.

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So I'm going to type INSERT space INTO space contacts space VALUES parentheses.

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Then I'm going to type 3 comma space and single quote bob single quote common 5678 comma

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and a single quote bob@hisemail

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dot com single quote right parentheses and a semi-colon. Press enter, and no output usually is a good sign

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that the command that we've typed has worked. We can confirm that by typing SELECT space * space FROM space contacts

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semicolon, and now we've got an extra record showing there so we're good to go.

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And by the way, if you're used to recalling previous commands by pressing the up arrow key -

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I'll try that 

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now - this doesn't work in sqlite from the command line in the Linux shell on the emulators. And that's

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fair enough because there's not much point Google including all the bells and whistles,

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when we don't spend much time using the shell. It's just a waste of the device's storage.

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So you just do have to type the commands in each time to get them to work.

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Alright so let's now swing back to Android Studio, now that we've added that record to the database, or more

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specifically back to our code.

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Now we've got a problem here at the moment - a slight problem. If we run the app again it's going to drop

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the table

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and wipe out our data that we've just added - the new record.

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So what I'm going to do is comment out this code, and basically I'm going to comment out the code all the

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way after the val database definition on line 23, all the way down to the query.

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So right down here,

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right down to there. So I'm going to comment that out,

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and I'm also going to comment out this last line down here, because obviously now that code isn't going to work,

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given that we've already commented out the other code that created the generated ID variable. Now that

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I've done that, we should be able to run our application and see those entries from the database

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on our emulator. We'll open up logcat as well.

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Give it a moment to start, and this time you can see that we've successfully,

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we are successfully seeing three entries there, number one, two and three,

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and the third one was obviously Bob, was the entry that we just added from the sqlite3 command line

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on our emulator.

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Alright so that's a very basic introduction to the Android file system, and accessing the sqlite database

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that your Android app creates on an emulator.

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It's very useful to be able to do that so that you can check the data that your app's writing to the

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database. Being able to check what's being written to the database can make debugging a lot easier.

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Now this app didn't put very much in the database and, as I've said, it's certainly not the way you should write

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a database app,

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but if you're trying to debug a database app then this technique is very useful.

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Just before I finish, what we're going to do is we'll close this logcat window down. We'll go back to our terminal and

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we'll exit out of there. So I'm going to type dot exit, to exit sqlite3, then I'm going to type exit which exits from super

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user mode, exit again which exits from the shell.

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Then exit one more time which closes the terminal pane in Android Studio.

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Alright so in the next videos we're going to start to see how to do this all properly, using a content

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provider for working with databases in Android apps.

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See you in the next video.