Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Inserts, updates, deletes and reads are generally OK from multiple threads, but Brad's <a href="https://stackoverflow.com/a/2493839/2759862">answer</a> is not correct. You have to be careful with how you create your connections and use them. There are situations where your update calls will fail, even if your database doesn't get corrupted.</p> <p><strong>The basic answer.</strong></p> <p>The SqliteOpenHelper object holds on to one database connection. It appears to offer you a read and write connection, but it really doesn't. Call the read-only, and you'll get the write database connection regardless.</p> <p>So, one helper instance, one db connection. Even if you use it from multiple threads, one connection at a time. The SqliteDatabase object uses java locks to keep access serialized. So, if 100 threads have one db instance, calls to the actual on-disk database are serialized.</p> <p>So, one helper, one db connection, which is serialized in java code. One thread, 1000 threads, if you use one helper instance shared between them, all of your db access code is serial. And life is good (ish).</p> <p>If you try to write to the database from actual distinct connections at the same time, one will fail. It will not wait till the first is done and then write. It will simply not write your change. Worse, if you don’t call the right version of insert/update on the SQLiteDatabase, you won’t get an exception. You’ll just get a message in your LogCat, and that will be it.</p> <p>So, multiple threads? Use one helper. Period. If you KNOW only one thread will be writing, you MAY be able to use multiple connections, and your reads will be faster, but buyer beware. I haven't tested that much.</p> <p>Here's a blog post with far more detail and an example app.</p> <ul> <li><a href="http://touchlabblog.tumblr.com/post/24474398246/android-sqlite-locking" rel="noreferrer">Android Sqlite Locking</a> (Updated link 6/18/2012)</li> <li><a href="https://github.com/touchlab/Android-Database-Locking-Collisions-Example" rel="noreferrer">Android-Database-Locking-Collisions-Example by touchlab</a> on GitHub</li> </ul> <p>Gray and I are actually wrapping up an ORM tool, based off of his Ormlite, that works natively with Android database implementations, and follows the safe creation/calling structure I describe in the blog post. That should be out very soon. Take a look.</p> <hr> <p>In the meantime, there is a follow up blog post:</p> <ul> <li><a href="http://touchlabblog.tumblr.com/post/24474750219/single-sqlite-connection" rel="noreferrer">Single SQLite connection</a></li> </ul> <p>Also checkout the fork by <em>2point0</em> of the previously mentioned locking example:</p> <ul> <li><a href="https://github.com/2point0/Android-Database-Locking-Collisions-Example" rel="noreferrer">Android-Database-Locking-Collisions-Example by 2point0</a> on GitHub</li> </ul>
    singulars
    1. This table or related slice is empty.
    1. POWhat are the best practices for SQLite on Android?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USKevin Galligan
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWhat are the best practices for SQLite on Android?
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. COAs an aside, Ormlite's android support can be found at http://ormlite.sourceforge.net/sqlite_java_android_orm.html. There are sample projects, documentation, and jars.
      singulars
      1. PO
      1. USGray
    2. COA second aside. The ormlite code has helper classes that can be used to manage dbhelper instances. You can use the ormlite stuff, but its not required. You can use the helper classes just to do connection management.
      singulars
      1. PO
      1. USKevin Galligan
    3. COKāgii, thank you for the detailed explanation. Could you clarify one thing -- I understand you should have ONE helper, but should you also only have one connection (i.e. one SqliteDatabase object)? In other words, how often should you call getWritableDatabase? And equally importantly when do you call close()?
      singulars
      1. PO
      1. USArtem
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload