如何在android中创建数据库？
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How do I create a database in android?
提问by prakrati
I need a step by step procedure for creating a database in Android.
我需要一个在 Android 中创建数据库的分步过程。
回答by AlphaMale
Database is important thing in programming. Many of our codes always use data to be processed and saved. Just like any other programming environment, Android supports database programming too. You can use the default database supported by android, SQLiteDatabase.
数据库在编程中很重要。我们的许多代码总是使用要处理和保存的数据。就像任何其他编程环境一样，Android 也支持数据库编程。可以使用android支持的默认数据库，SQLiteDatabase.
Database in SQLiteDatabase can contain more than one table.Assume that we have one database PERSONALDBand one table BIODATA. The structure of BIODATAis:
SQLiteDatabase 中的数据库可以包含多个PERSONALDB表BIODATA。假设我们有一个数据库和一个表。的结构BIODATA是：
_id integer
code string
name string
gender string
_id is for key increment,
code, name, and genderis for description of person.
code, name, 和gender用于描述person。
When program is called for the first time, we have to make sure that the database and the table is opened, if it exists.If not, then we have to create a database and a table. As an example from Android notepad sample, here is the class PersonDbHelperfor manipulating table Biodata.
第一次调用程序时，我们必须确保数据库和表是打开的，如果存在。如果不存在，那么我们必须创建一个数据库和一个表。作为一个例子Android notepad sample，这里是PersonDbHelper操作表的类Biodata。
import java.io.FileNotFoundException;
import java.util.ArrayList;
import java.util.List;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.util.Log;
public class PersonDbHelper {
class Row extends Object {
public long _Id;
public String code;
public String name;
public String gender;
}
private static final String DATABASE_CREATE =
"create table BIODATA(_id integer primary key autoincrement, "
+ "code text not null,"
+ "name text not null"
+");";
private static final String DATABASE_NAME = "PERSONALDB";
private static final String DATABASE_TABLE = "BIODATA";
private static final int DATABASE_VERSION = 1;
private SQLiteDatabase db;
public PersonDbHelper(Context ctx) {
try {
db = ctx.openDatabase(DATABASE_NAME, null);
} catch (FileNotFoundException e) {
try {
db =
ctx.createDatabase(DATABASE_NAME, DATABASE_VERSION, 0,
null);
db.execSQL(DATABASE_CREATE);
} catch (FileNotFoundException e1) {
db = null;
}
}
}
public void close() {
db.close();
}
public void createRow(String code, String name) {
ContentValues initialValues = new ContentValues();
initialValues.put("code", code);
initialValues.put("name", name);
db.insert(DATABASE_TABLE, null, initialValues);
}
public void deleteRow(long rowId) {
db.delete(DATABASE_TABLE, "_id=" + rowId, null);
}
public List<Row> fetchAllRows() {
ArrayList<Row> ret = new ArrayList<Row>();
try {
Cursor c =
db.query(DATABASE_TABLE, new String[] {
"_id", "code", "name"}, null, null, null, null, null);
int numRows = c.count();
c.first();
for (int i = 0; i < numRows; ++i) {
Row row = new Row();
row._Id = c.getLong(0);
row.code = c.getString(1);
row.name = c.getString(2);
ret.add(row);
c.next();
}
} catch (SQLException e) {
Log.e("Exception on query", e.toString());
}
return ret;
}
public Row fetchRow(long rowId) {
Row row = new Row();
Cursor c =
db.query(true, DATABASE_TABLE, new String[] {
"_id", "code", "name"}, "_id=" + rowId, null, null,
null, null);
if (c.count() > 0) {
c.first();
row._Id = c.getLong(0);
row.code = c.getString(1);
row.name = c.getString(2);
return row;
} else {
row.rowId = -1;
row.code = row.name= null;
}
return row;
}
public void updateRow(long rowId, String code, String name) {
ContentValues args = new ContentValues();
args.put("code", code);
args.put("name", name);
db.update(DATABASE_TABLE, args, "_id=" + rowId, null);
}
public Cursor GetAllRows() {
try {
return db.query(DATABASE_TABLE, new String[] {
"_id", "code", "name"}, null, null, null, null, null);
} catch (SQLException e) {
Log.e("Exception on query", e.toString());
return null;
}
}
}
In the method onCreate, you just have to put a single command given below to initialize the database :
...
在该方法中onCreate，您只需要输入下面给出的单个命令来初始化数据库：...
Db = new PersonDbHelper(this);
...
...
It will try to open 'PersonalDB' first.If it does not exist, then it will create a database. In this 'PersonDbHelper' class, you have methods for inserting, deleting, updating, querying the table.
它会先尝试打开“PersonalDB”。如果它不存在，那么它会创建一个数据库。在这个“PersonDbHelper”类中，您有插入、删除、更新、查询表的方法。
Here is the reference to above tutorial:
这是对上述教程的参考：
Creating my first android Database
You may also go through:
您还可以通过：
http://www.devx.com/wireless/Article/40842
http://www.devx.com/wireless/Article/40842
http://www.vogella.de/articles/AndroidSQLite/article.html
http://www.vogella.de/articles/AndroidSQLite/article.html
Hope this helps.
希望这可以帮助。
回答by prakrati
Create database:
创建数据库：
db= this.openOrCreateDatabase("db_hw3", MODE_PRIVATE, null);
回答by Snake
This will do the trick: http://www.devx.com/wireless/Article/40842/1954
回答by Alexander Oleynikov
Note that it's a good practice to wrap all your data access to ContentProviders
请注意，将所有数据访问权限封装到ContentProviders是一个好习惯
