Android SQLite简单使用

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

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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。