When is SQLiteOpenHelper onCreate() / onUpgrade() run?

问题

I have created my tables in my SQLiteOpenHelper onCreate() but receive

SQLiteException: no such table

or

SQLiteException: no such column

errors. Why?

NOTE:

(This is the amalgamated summary of tens of similar questions every week. Attempting to provide a \"canonical\" community wiki question/answer here so that all those questions can be directed to a good reference.)

回答1:

SQLiteOpenHelper onCreate() and onUpgrade() callbacks are invoked when the database is actually opened, for example by a call to getWritableDatabase(). The database is not opened when the database helper object itself is created.

SQLiteOpenHelper versions the database files. The version number is the int argument passed to the constructor. In the database file, the version number is stored in PRAGMA user_version.

onCreate() is only run when the database file did not exist and was just created. If onCreate() returns successfully (doesn't throw an exception), the database is assumed to be created with the requested version number. As an implication, you should not catch SQLExceptions in onCreate() yourself.

onUpgrade() is only called when the database file exists but the stored version number is lower than requested in constructor. The onUpgrade() should update the table schema to the requested version.

When changing the table schema in code (onCreate()), you should make sure the database is updated. Two main approaches:

1. Delete the old database file so that onCreate() is run again. This is often preferred at development time where you have control over the installed versions and data loss is not an issue. Some ways to to delete the database file:

   • Uninstall the application. Use the application manager or adb uninstall your.package.name from shell.

   • Clear application data. Use the application manager.

2. Increment the database version so that onUpgrade() is invoked. This is slightly more complicated as more code is needed.

   • For development time schema upgrades where data loss is not an issue, you can just use execSQL("DROP TABLE IF EXISTS <tablename>") in to remove your existing tables and call onCreate() to recreate the database.

   • For released versions, you should implement data migration in onUpgrade() so your users don't lose their data.

回答2:

To further add missing points here, as per the request by Jaskey

Database version is stored within the SQLite database file.

catch is the constructor

SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)

So when the database helper constructor is called with a name (2nd param), platform checks if the database exists or not and if the database exists, it gets the version information from the database file header and triggers the right call back

As already explained in the older answer, if the database with the name doesn't exists, it triggers onCreate.

Below explanation explains onUpgrade case with an example.

Say, your first version of application had the DatabaseHelper (extending SQLiteOpenHelper) with constructor passing version as 1 and then you provided an upgraded application with the new source code having version passed as 2, then automatically when the DatabaseHelper is constructed, platform triggers onUpgrade by seeing the file already exists, but the version is lower than the current version which you have passed.

Now say you are planing to give a third version of application with db version as 3 (db version is increased only when database schema is to be modified). In such incremental upgrades, you have to write the upgrade logic from each version incrementally for a better maintainable code

Example pseudo code below:

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
  switch(oldVersion) {
    case 1:
       //upgrade logic from version 1 to 2
    case 2:
       //upgrade logic from version 2 to 3
    case 3:
       //upgrade logic from version 3 to 4
       break;
    default:
       throw new IllegalStateException(
                "onUpgrade() with unknown oldVersion " + oldVersion);
  }
}

Notice the missing break statement in case 1 and 2. This is what I mean by incremental upgrade.

Say if the old version is 2 and new version is 4, then the logic will upgrade the database from 2 to 3 and then to 4

If old version is 3 and new version is 4, it will just run the upgrade logic for 3 to 4

回答3:

onCreate()

1. When we create DataBase at a first time (i.e Database is not exists) onCreate() create database with version which is passed in SQLiteOpenHelper(Context context, String name, SQLiteDatabase.CursorFactory factory, int version)

2. onCreate() method is creating the tables you’ve defined and executing any other code you’ve written. However, this method will only be called if the SQLite file is missing in your app’s data directory (/data/data/your.apps.classpath/databases).

3. This method will not be called if you’ve changed your code and relaunched in the emulator. If you want onCreate() to run you need to use adb to delete the SQLite database file.

onUpgrade()

1. SQLiteOpenHelper should call the super constructor.
2. The onUpgrade() method will only be called when the version integer is larger than the current version running in the app.
3. If you want the onUpgrade() method to be called, you need to increment the version number in your code.

回答4:

May be I am too late but I would like to share my short and sweet answer. Please check Answer for a same problem. It will definitely help you. No more deep specifications.

If you are confident about syntax for creating table, than it may happen when you add new column in your same table, for that...

1) Uninstall from your device and run it again.

OR

2) Setting -> app -> ClearData

OR

3) Change DATABASE_VERSION in your "DatabaseHandler" class (If you have added new column than it will upgrade automatically)

public DatabaseHandler(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

OR

4) Change DATABASE_NAME in your "DatabaseHandler" class (I faced same problem. But I succeed by changing DATABASE_NAME.)

回答5:

Points to remember when extending SQLiteOpenHelper

1. super(context, DBName, null, DBversion); - This should be invoked first line of constructor
2. override onCreate and onUpgrade (if needed)
3. onCreate will be invoked only when getWritableDatabase() or getReadableDatabase() is executed. And this will only invoked once when a DBName specified in the first step is not available. You can add create table query on onCreate method
4. Whenever you want to add new table just change DBversion and do the queries in onUpgrade table or simply uninstall then install the app.

回答6:

onCreate is called for the first time when creation of tables are needed. We need to override this method where we write the script for table creation which is executed by SQLiteDatabase. execSQL method. After executing in first time deployment, this method will not be called onwards.

onUpgrade This method is called when database version is upgraded. Suppose for the first time deployment , database version was 1 and in second deployment there was change in database structure like adding extra column in table. Suppose database version is 2 now.

回答7:

You can create database & table like

public class DbHelper extends SQLiteOpenHelper {
private static final String DBNAME = "testdatbase.db";
private static final int VERSION = 1;

public DbHelper(Context context) {
    super(context, DBNAME, null, VERSION);
    // TODO Auto-generated constructor stub
}

@Override
public void onCreate(SQLiteDatabase db) {
    // TODO Auto-generated method stub
    db.execSQL("create table BookDb(id integer primary key autoincrement,BookName text,Author text,IssuedOn text,DueDate text,Fine text,Totalfine text");

}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS BookDb");
    onCreate(db);
  }
}

Note : if you want create another table or add columns or no such table, just increment the VERSION

回答8:

Sqlite database override two methods

1) onCreate(): This method invoked only once when the application is start at first time . So it called only once

2)onUpgrade() This method called when we change the database version,then this methods gets invoked.It is used for the alter the table structure like adding new column after creating DB Schema

回答9:

no such table found is mainly when you have not opened the SQLiteOpenHelper class with getwritabledata() and before this you also have to call make constructor with databasename & version. And OnUpgrade is called whenever there is upgrade value in version number given in SQLiteOpenHelper class.

Below is the code snippet (No such column found may be because of spell in column name):

public class database_db {
    entry_data endb;
    String file_name="Record.db";
    SQLiteDatabase sq;
    public database_db(Context c)
    {
        endb=new entry_data(c, file_name, null, 8);
    }
    public database_db open()
    {
        sq=endb.getWritableDatabase();
        return this;
    }
    public Cursor getdata(String table)
    {
        return sq.query(table, null, null, null, null, null, null);
    }
    public long insert_data(String table,ContentValues value)
    {
        return sq.insert(table, null, value);
    }
    public void close()
    {
        sq.close();
    }
    public void delete(String table)
    {
        sq.delete(table,null,null);
    }
}
class entry_data extends SQLiteOpenHelper
{

    public entry_data(Context context, String name, SQLiteDatabase.CursorFactory factory,
                      int version) {
        super(context, name, factory, version);
        // TODO Auto-generated constructor stub
    }

    @Override
    public void onCreate(SQLiteDatabase sqdb) {
        // TODO Auto-generated method stub

        sqdb.execSQL("CREATE TABLE IF NOT EXISTS 'YOUR_TABLE_NAME'(Column_1 text not null,Column_2 text not null);");

    }

    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
          onCreate(db);
    }

}

回答10:

If you forget to provide a "name" string as the second argument to the constructor, it creates an "in-memory" database which gets erased when you close the app.

回答11:

Uninstall your application from the emulator or device. Run the app again. (OnCreate() is not executed when the database already exists)

回答12:

Your database name must end with .db also your query strings must have a terminator (;)

回答13:

Recheck your query in ur DatabaseHandler/DatabaseManager class(which ever you have took)

回答14:

Sqliteopenhelper's method have methods create and upgrade,create is used when any table is first time created and upgrade method will called everytime whenever table's number of column is changed.

来源：https://stackoverflow.com/questions/21881992/when-is-sqliteopenhelper-oncreate-onupgrade-run