一直都是用的数据库框架,今天复习的时候忽然发现好像不怎么会使用SQLite了,复习一下吧。
首先继承创建一个SQLite辅助类SqlHelper,继承SQLiteOpenHelper
一、SQLiteOpenHelper
public class SqlHelper extends SQLiteOpenHelper {
//数据库名
private static final String DB_NAME = "test_db";
//数据库版本
private static final int DB_VERSION = 1;
public static SqlHelper instance;
public static SqlHelper getInstance(){
if (instance == null){
instance = new SqlHelper(MyApp.context);
}
return instance;
}
/**
* @param context 上下文
* 数据库名称
* 数据库游标工厂类(可选)
* 数据库版本
*/
public SqlHelper(@Nullable Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
//创建教师表
db.execSQL(TeacherTable.CREATE_TABLE);
//创建学生表
db.execSQL(StudentTable.CREATE_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
String drop = "DROP TABLE IF EXISTS ";
//drop older table existed
db.execSQL(drop + StudentTable.TABLE_NAME);
db.execSQL(drop + TeacherTable.TABLE_NAME);
onCreate(db);
}
/**
* 插入
*
* @param tableName 表名
* @param values
* @return 插入是否成功
*/
public boolean insert(String tableName, ContentValues values) {
SQLiteDatabase db = this.getWritableDatabase();
long res = db.insert(tableName, null, values);
return res != -1;
}
/**
* 根据ID删除
* @param tableName 表名
* @param id
* @return
*/
public boolean delete(String tableName, String id) {
try {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(tableName, "id = ?", new String[]{id});
return true;
} catch (NumberFormatException e) {
e.printStackTrace();
}
return false;
}
/**
* 根据条件删除
* @param tableName
* @param where
* @param args
* @return
*/
public boolean delete(String tableName, String where, String[] args) {
try {
SQLiteDatabase db = this.getWritableDatabase();
db.delete(tableName, where, args);
return true;
} catch (Exception e) {
e.printStackTrace();
}
return false;
}
/**
* 修改
* @param tableName
* @param id
* @param values
* @return
*/
public boolean update(String tableName, String id, ContentValues values) {
try {
SQLiteDatabase db = this.getWritableDatabase();
db.update(tableName, values, TeacherTable.COLUMN_ID + " = ? ", new String[]{id});
return true;
} catch (Exception e) {
e.printStackTrace();
Log.e("tag","update Exception: " + e.toString());
}
return false;
}
/**
* 查询
* @param tableName
* @param columns
* @param selection
* @param selectionArgs
* @return
*/
public Cursor query(String tableName, String[] columns, String selection, String[] selectionArgs) {
try {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.query(tableName, columns, selection, selectionArgs, null, null, null);
return cursor;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 根据ID查询
* @param tableName
* @param id
* @return
*/
public Cursor rawQuery(String tableName, String id) {
try {
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery("SELECT * FROM " + tableName + " WHERE ID = " + id, null);
return cursor;
} catch (Exception e) {
e.printStackTrace();
}
return null;
}
/**
* 查询Sql语句
* @param sql
*/
public void rawQuery(String sql) {
SQLiteDatabase db = this.getReadableDatabase();
db.rawQuery(sql, null);
}
}
除了构造方法、onCreate
和onUpgrade
是必须的。其余的增删改查方式都是自己实现的。
二、创建表
在onCreate
方法中会执行表的创建操作:
@Override
public void onCreate(SQLiteDatabase db) {
//创建教师表
db.execSQL(TeacherTable.CREATE_TABLE);
//创建学生表
db.execSQL(StudentTable.CREATE_TABLE);
}
为了方便处理,这里将表创建的sql语句拿到TeacherTable
和StudentTable
类中了,每个类代表一张表。
这样的好处是当不止一张表的时候,表的结构会比较清晰。如果只创建一张表的话,在SqlHelper
中初始化即可。
TeacherTable
public class TeacherTable {
//表名
public static final String TABLE_NAME = "teacher";
//列
public static final String COLUMN_ID = "id";
public static final String COLUMN_NAME = "name";
public static final String COLUMN_GRADE = "grade";
public static final String COLUMN_CLS = "cls";
//创建teacher表
public static final String CREATE_TABLE = "CREATE TABLE " //"CREATE TABLE IF NOT EXISTS "
+ TABLE_NAME + "("
+ COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
+ COLUMN_NAME + " TEXT,"
+ COLUMN_GRADE + " TEXT,"
+ COLUMN_CLS + " TEXT"
+ ")";
private int id;
private String name;
private String grade;
private String cls;
}
StudentTable
public class StudentTable {
//表名
public static final String TABLE_NAME = "student";
//列名
public static final String COLUMN_ID = "id";
public static final String COLUMN_NAME = "name";
public static final String COLUMN_GRADE = "grade";
public static final String COLUMN_CLS = "cls";
//创建student表
public static final String CREATE_TABLE = "CREATE TABLE "
+ TABLE_NAME + " ("
+ COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT,"
+ COLUMN_NAME + " TEXT,"
+ COLUMN_GRADE + " TEXT,"
+ COLUMN_CLS + " TEXT"
+ ")";
private int id;
private String name;
private String grade;
private String cls;
}
后面的增删改查就是SQL语句的执行。
三、使用
1、增加
ContentValues values = new ContentValues();
values.put(TeacherTable.COLUMN_NAME, mTeachName);
values.put(TeacherTable.COLUMN_GRADE,"1");
values.put(TeacherTable.COLUMN_CLS,"3");
values.put(TeacherTable.COLUMN_ID, id);
mSqlHelper.insert(TeacherTable.TABLE_NAME, values);
mTeachName
是随便输入的字符串
2、删除
mSqlHelper.delete(TeacherTable.TABLE_NAME,TeacherTable.COLUMN_NAME + " = ?", new String[]{mTeachName});
这里面是根据姓名删除的,当然也可以根据ID删除。
3、修改
ContentValues contentValues = new ContentValues();
contentValues.put(TeacherTable.COLUMN_NAME, "张三");
contentValues.put(TeacherTable.COLUMN_GRADE, "9");
contentValues.put(TeacherTable.COLUMN_CLS, "13");
// contentValues.put(TeacherTable.COLUMN_ID, 111);
mSqlHelper.update(TeacherTable.TABLE_NAME, "1", contentValues);
根据ID修改,也可以把ID成新的修改。
4、查询
Cursor cursor = mSqlHelper.query(TeacherTable.TABLE_NAME,null,"name = ?", new String[]{mTeachName});
if (cursor == null){
return;
}
cursor.moveToFirst();
StringBuffer sb = new StringBuffer();
while (!cursor.isAfterLast()){
sb.append("ID:" + cursor.getInt(cursor.getColumnIndex(TeacherTable.COLUMN_ID))
+ " name:" + cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_NAME))
+ " grade:"+ cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_GRADE))
+ " cls: " + cursor.getString(cursor.getColumnIndex(TeacherTable.COLUMN_CLS))
+ "\n"
);
cursor.moveToNext();
}
cursor.close();
上面是根据姓名查询。
总结
当创建好SQLiteOpenHelper
的实现类,并执行构造方法创建数据库,执行onCreate
和onUpgrade
。后面的增删改查基本就是SQL语句的执行了。