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This article mainly explains "how to insert the data into the database correctly by Android". The explanation in the article is simple and clear, easy to learn and understand. Please follow the editor's train of thought to study and learn "how to insert the data into the database correctly by Android".

Define patterns and constraints

One of the main principles of SQL data is the schema: a formal statement of how the database is organized. The schema is reflected in the SQL statements you use to create the database. You may find that it helps to create a companion class, the contract class, which uses a systematic and self-recording way to explicitly specify the layout of your pattern.

The contract class is a constant container that defines URIs, table names, and column names. All classes in the same package can use the constants in this constraint class. In this way, it will be modified in one place, and it will be valid globally.

A good way to organize a constraint class is to put the definition at the root level of the class so that it is valid for the entire database.

Note: by implementing the BaseColumns interface, your inner class will inherit a primary key called _ ID, which some Android classes (such as cursor adapters) will want to have. It is not required, however, this field will help your database work more harmoniously with the Android framework.

For example, the following code snippet defines the table and column names of a table:

PublicstaticabstractclassFeedEntryimplementsBaseColumns {

Public static final String TABLE_NAME = "entry"

Public static final String COLUMN_NAME_ENTRY_ID = "entryid"

Public static final String COLUMN_NAME_TITLE = "title"

Public static final String COLUMN_NAME_SUBTITLE = "subtitle"

...

}

To prevent the constraint class from being accidentally instantiated, its constructor is private:

/ / Prevents the FeedReaderContract class from being instantiated.

Private FeedReaderContract () {}

Use the SQL helper to create the database

Once you have defined your database, you should implement the method of creating and maintaining databases and tables. The following are typical statements for creating and deleting tables:

PrivatestaticfinalString TEXT_TYPE = "

TEXT "

Private static final String COMMA_SEP = ","

Private static final String SQL_CREATE_ENTRIES =

"CREATE TABLE" + FeedReaderContract.FeedEntry.TABLE_NAME + "(" +

FeedReaderContract.FeedEntry._ID + "INTEGER PRIMARY KEY," +

FeedReaderContract.FeedEntry.COLUMN_NAME_ENTRY_ID + TEXT_TYPE + COMMA_SEP +

FeedReaderContract.FeedEntry.COLUMN_NAME_TITLE + TEXT_TYPE + COMMA_SEP +

... / / Any other options for the CREATE command

")"

Private static final String SQL_DELETE_ENTRIES =

"DROP TABLE IF EXISTS" + TABLE_NAME_ENTRIES

Just as you save files in the device's internal memory, Android saves your database in the private hard disk space associated with the application. Because this area is inaccessible to other applications by default, your data is secure.

It is beneficial to use a set of API in the SQLiteOpenHelper class. Because when using this class to obtain a reference to the database, the system will only perform potentially long-term operations to create and update the database when needed and during the non-startup of the application. All you need to do is call the getWritableDatabase () or getReadableDatabase () method.

Note: because they are long-running operations, you must make sure that the getWritableDatabase () and getReadableDatabase () methods are called in the background thread, such as in AsyncTask or IntentService.

To use SQLiteOpenHelper, you inherit the SQLiteOpenHelper class to create a subclass and override the onCreate (), onUpgrade (), and onOpen () callback methods, and optionally implement the onDowngrade () callback method.

For example, the following is a subclass implementation of the SQLiteOpenHelper class:

PublicclassFeedReaderDbHelperextendsSQLiteOpenHelper {

/ / If you change the database schema, you must increment the database version.

Public static final int DATABASE_VERSION = 1

Public static final String DATABASE_NAME = "FeedReader.db"

Public FeedReaderDbHelper (Context context) {

Super (context, DATABASE_NAME, null, DATABASE_VERSION)

}

Public void onCreate (SQLiteDatabase db) {

Db.execSQL (SQL_CREATE_ENTRIES)

}

Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion) {

/ / This database is only a cache for online data, so its upgrade policy is

/ / to simply to discard the data and start over

Db.execSQL (SQL_DELETE_ENTRIES)

OnCreate (db)

}

Public void onDowngrade (SQLiteDatabase db, int oldVersion, int newVersion) {

OnUpgrade (db, oldVersion, newVersion)

}

}

Use the following methods to access your database:

FeedReaderDbHelper mDbHelper = newFeedReaderDbHelper (getContext ())

Thank you for your reading, the above is the content of "how to insert the data into the database correctly by Android". After the study of this article, I believe you have a deeper understanding of how to insert the data into the database correctly by Android, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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