Background: I'm taking an Android class right now and part of our final project requires retrieving data through an SQLite query. We're using the Chrome browser history to populate a RecyclerView. We're working off of an AVD and changed permissions on the history file (since, obviously, this isn't something that would normally be done) to make it readable. We have to use a SQLite query to get the data, though, and then do other stuff with it inside the app.
I've been digging around for the past couple of days and have found quite a few different examples for database connections in Android but they all seem to have a lot of unnecessary bloat that I don't need. I don't need to create or delete tables, I'm not adding or changing entries at all, I just need to query and get information back to play around with. I looked through the SQLiteDatabase documentation and the only thing that kind of looked like what I wanted would involve the beginTransaction() and endTransaction() methods. But I wasn't entirely sure.
I'm definitely not trying to like, covertly get others to do the work for me, but I wonder: is there a way I can query the database directly with a few lines in my code or from a relatively simple method? Or do I need to go through and implement something resembling the various database helper classes I've seen with all the extra functionality I don't need right now? Feel free to ask any follow up questions that may arise, if any. Thanks for any help you all can give!
You probably want to use one of the SQLiteDatabase.openDatabase() methods, with the OPEN_READONLY flag. Then, you can use methods like query() or compileStatement() on the returned SQLiteDatabase object.
Related
The problem
I need to do a T9 contact search for an Android project I'm working on. Now, it would be simple if I just had to pull contacts from the native contacts storage and then do T9 on that, but the problem I have is that I have an additional local database where we store extra content for some contacts in the form of additional numbers that our application displays and handles. I need to do a search based on the contact’s name, number, and the extra numbers (if any) contained in the local database. The local database has IDs that match those of the contacts in the native Android database.
I have been looking for a solution to this problem, and I have gone through these ideas, but none of them seem to be the right solution.
Try #1
Write a ContentProvider for our local database, in order to be able to perform a simple join operation between the native Android contacts table and our table, however, it seems that joining tables via ContentProviders is only possible when you write your own ContentProvider, thus making this solution not viable for me, not to mention that Android documentation states that you should not write a ContentProvider if you don’t want to share your data with other applications, which we currently don’t.
Try #2
Copy all the needed data from Android’s contacts database into our database, and use ContentObservers to update it constantly. This solution had two major problems: 1) It seemed to have a big overhead, not just on the processor of the device, but also on the development, as we would have to introduce some really delicate update/read/write mechanisms and ensure that our data always stays relatively fresh, while also being performant; 2) A colleague has stated that during contact sync, the ContentObserver fires off events very often, thus making a need for special code to delay the updating, which he says has never really worked out great.
Try #3
Use a CursorJoiner to join the two cursors that I have received and then use a MatrixCursor to display all the data, but that solution is not viable since all the data would be kept in memory, and we are working with datasets that have more than 10k rows of data. Even if the memory could handle it, it would be slow to load, which for T9, isn’t really an option. This also pretty much excludes any solution that doesn't use a Cursor to look over data, which is why I am going in that direction.
Question
Am I missing something obvious? If I am, please point me in the right way. All of the things that I have tried don’t seem feasible to me, but I’m open to someone modifying them in order to make them worthwhile.
I'll begin with explaining how I stumbled upon SQLite Asset Helper library. I am trying to build a small android application which is basically shows the meaning of words. And to do so I intend to keep everything offline (no dependence of internet connectivity). Now, as far as I can think of, there are 2 ways of achieving that:
1. Using String array, which I believe will be a tedious task and a memory hog.
2. By providing a pre-populated database, using which I can easily establish relations between words and their meanings and do more (searching, sorting, etc).
Now, the problem I am facing is supplying a pre-populated database (or words and meanings) with the app itself. And for doing that I came across SQLite Asset Helper which does the job.
I have read a number of articles related to SQlite Asset Helper but not many which confirm its implementation on latest iterations of Android. Also, is the only possible solution to deliver a pre-populated database to the user (without needing to go online)? Is it acceptable method? Any other better alternative up for suggestion would be great!
I have read a number of articles related to SQlite Asset Helper but not many which confirm its implementation on latest iterations of Android
It works on the latest iterations of Android.
Also, is the only possible solution to deliver a pre-populated database to the user (without needing to go online)?
You are welcome to roll your own implementation. I do not know what you would gain by this.
Is it acceptable method?
I am not aware of anything better.
I have a SQLite database which has a table (of course) named Object. In my application, I need to access that table and all of its fields. I am able to query the database and get all of the information I want from a cursor with no issues. The problem comes with deciding what to do with the cursor next. Right now I am thinking of creating a class called Object and it will have fields for every column in the table which will be set by the query. This just seems so... inefficient. I'm not sure how to do this without needing to write out every column that is in the table for the object to use, which seems to violate DRY. Are there any better ways to do this?
My end goal is to be able to access every row in the table and get whatever information I want for that row. For example I will be using this to populate a ListView. If this is too ambiguous let me know and I'll try to clarify.
Thanks!
Edit: I've found the library db40 and it seems to do what I want. The library seems to be kind of big though (40 mb) for a mobile application. Does anybody have experience with this? Everything I've read seems to indicate it is good. I'll post more if I find information.
Are there any better ways to do this?
This is very "wide" question and depends on personal requirements and what is for developer more comfortable. I'm using your idea that is for me the best one you can use.
Generally we can say you want to create ORM (object-relation mapping). It's very clean and efficient approach (my opinion). Of course sometimes is not the best solution to use ORM ( i never met with this case but heard about it). I almost always use my own defined ORM for sure it takes some time but results are significant against done frameworks.
Both have advantages and disadvantages. Own ORM has much more higher performance because it's designated and optimized for concrete solution (mainly queries etc.).
I suggest you to do what you mentioned -> create object that will represent table in database with properties equal to columns. I'm using this in work and we never had problems with performance or too much battery consumption with our applications.
It's also much more safe if you'll show user some data not directly from database but "copies" in objects. Users can do whatever want with dislayed results (they can add some dangerous symbols and hacks) but now you can easily check this before you'll want to update database(s) with changes.
Your source-code looks good, another developer won't be lost in your code, everything will be clear and easy to do updates for future.
I provided you "my opinion" on this thing so hope it'll help you with make a decision.
EDIT: Assume a rooted phone for this post.
I deleted a previous question I posted on this topic because none of the answers even came close to answering the question. Long story short, I need to open a database and modify an existing record. I do not want to use a "helper class" because I actually want to see and understand what is going on in a few lines of code rather than an unnecessary (for my purposes) class that contains 100 lines of code. So please don't tell me to "use the notepad tutorial." I have, and it doesn't explain what I need.
To simplify, here is what I am doing:
SQLiteDatabase myDB = this.openOrCreateDatabase("/data/data/MY_APP/databases/settings.db", MODE_PRIVATE, null);
myDB.execSQL("INSERT INTO my_table (SOME_FIELD) VALUES ('SOME_VALUE');");
This works very nicely. However it fails if I try to open/edit a database in a different path. For example I might want to edit a database that another app uses. How can I do this? Is it a simple matter of permissions? Should it work if my app requests and gets root access?
EDIT: There are tons of apps I can install on my phone that are capable of editing every single database on the system so obviously this CAN be done.
Regarding Android security, you cannot access others' app DB directly. If other applications create ContentProvider then you can access theirs DBs (if exist) through its Providers. Otherwise, there's no way out AFAIK.
I don't know if you are still looking for this answer. I was looking to do the same but couldn't really find anything. I knew I needed to use root for the process, but again, couldn't find anything. I started messing around and just trying a lot of random things, and finally found a way to do it.
The short version that worked for me is you need to, as root, change the permissions of the database, access it directly (not through an sqlite helper), do whatever you wish, and then put the permissions back. I detail all of this on my blog:
http://rratmansky.wordpress.com/?p=259&preview=true
I have seen this question here, and was wondering if the same method of "pre-loading" a database for an android application still works. I will be developing my application on the 2.2 platform, but I want to make sure that going forward I will not have to completely redesign if I use this method.
Secondly, is this the best method if I have unchanging data that needs to be looked up? Or is XML a better choice?
Example: I have a Car, a car has attributes like weight, color, make, model, engine, etc. these all need to be accessed in a lookup but the attributes and entries will never change (and if they do, they change as such a slow rate that I would release an update to add the few things that changed).
Thanks for any help.
Yes, the pre-loading method mentioned in the blogpost that article links to (http://www.reigndesign.com/blog/using-your-own-sqlite-database-in-android-applications/) still works for me after some tweaks prompted by a number of force closes from users. There were some issues with the database not being found on the Desire HD, which caused problems. It was difficult to isolate what exactly the problem was, but I think it was the file locations that was the problem. You should define
private static String DB_PATH = Environment.getDataDirectory() + "/data/your/app/package/databases/"
instead of
private static String DB_PATH = "/data/data/your/app/domain/databases/"
I also changed all database access to writeable as I had read that caused problems, but not sure if that was really the issue.
In terms of your second question, I would say it depends on exactly how much data you have. If it's a lot of data, you're probably better off using a database anyway for performance reasons. There are pitfalls to using the SQLite APIs, such as apostrophes in the fields (make sure you use the convenience methods query, update and insert rather than rawQuery). But I'm sure there are with XML too - I don't think there's any "correct" method more what you are most comfortable with - i.e. do you prefer working with databases or raw XML? If neither, and you're not planning to do major updating or querying, I would use XML, or even JSON, because of the reasons above and what Jodes alludes to.
The answer is not simple, you need to cross reference the version of SQLite used in different phones with the file format used for those versions.
A previous SO question showing difficulties in determining SQLite versions are here:
Version of SQLite used in Android?
And a page listing differences in file formats for different SQLite versions is here:
http://www.sqlite.org/formatchng.html