Android徒手撸数据库系列——实现单表的增删改查

本文主要是介绍Android徒手撸数据库系列——实现单表的增删改查，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

这是手撸数据库框架的第二篇

之前完成了一篇文章

Android徒手撸数据库系列——注解与反射数据库关系模型

下面继续上一篇没有完成的内容

   /*** Convenience method for updating rows in the database.** @param table the table to update in* @param values a map from column names to new column values. null is a*            valid value that will be translated to NULL.* @param whereClause the optional WHERE clause to apply when updating.*            Passing null will update all rows.* @param whereArgs You may include ?s in the where clause, which*            will be replaced by the values from whereArgs. The values*            will be bound as Strings.* @return the number of rows affected*/public int update(String table, ContentValues values, String whereClause, String[] whereArgs) {return updateWithOnConflict(table, values, whereClause, whereArgs, CONFLICT_NONE);}

我们可以看到多了参数whereClause和whereArgs

获取需要更新的字段与插入时相同

   Map<String, String> values = getValues(entity);ContentValues contentValues = getContentValues(values);

然后创建表示条件的对象

public class Condition {public String whereCause;//"name=? && password=?...."public String[] whereArgs;//new String[]{"ddssingsong"}// 构造查询语句public Condition(Map<String, String> whereCause) {ArrayList list = new ArrayList();StringBuilder stringBuilder = new StringBuilder();// 构造时忽略第一个and语句stringBuilder.append("1=1 ");Set keys = whereCause.keySet();Iterator iterator = keys.iterator();while (iterator.hasNext()) {String key = (String) iterator.next();String value = whereCause.get(key);if (value != null) {stringBuilder.append(" and " + key + "=?");list.add(value);}}this.whereCause = stringBuilder.toString();this.whereArgs = (String[]) list.toArray(new String[list.size()]);}
}

整个方法如下

 @Overridepublic int update(T entity, T where) {Map<String, String> values = getValues(entity);ContentValues contentValues = getContentValues(values);Map<String, String> whereCause = getValues(where);Condition condition = new Condition(whereCause);return mSqLiteDatabase.update(mTableName, contentValues, condition.whereCause, condition.whereArgs);}

2. 数据的删除

数据库删除和更新差不多

  @Overridepublic int delete(T where) {Map<String, String> map = getValues(where);Condition condition = new Condition(map);return mSqLiteDatabase.delete(mTableName, condition.whereCause, condition.whereArgs);}

3. 数据的查询

查询的话拿到Cursor后需要对返回结果进行处理

  private List<T> getResult(Cursor cursor, T where) {ArrayList<T> list = new ArrayList();T item;while (cursor.moveToNext()) {try {item = (T) where.getClass().newInstance();for (Map.Entry<String, Field> stringFieldEntry : cacheMap.entrySet()) {// 获取列名String columnName = (String) ((Map.Entry) stringFieldEntry).getKey();// 根据列名拿到游标的位置int columnIndex = cursor.getColumnIndex(columnName);Field field = (Field) ((Map.Entry) stringFieldEntry).getValue();Class type = field.getType();if (columnIndex != -1) {if (type == String.class) {//反射方式赋值field.set(item, cursor.getString(columnIndex));} else if (type == Double.class) {field.set(item, cursor.getDouble(columnIndex));} else if (type == Integer.class) {field.set(item, cursor.getInt(columnIndex));} else if (type == Long.class) {field.set(item, cursor.getLong(columnIndex));} else if (type == byte[].class) {field.set(item, cursor.getBlob(columnIndex));/*不支持的类型*/} else {continue;}}}list.add(item);} catch (InstantiationException e) {e.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}}return list;}

从之前缓存的字段信息中查询出对应的字段信息，然后使用反射对其赋值

下面是整个查询方法

   @Overridepublic List<T> query(T where, String orderBy, Integer startIndex, Integer limit) {Map map = getValues(where);String limitString = null;if (startIndex != null && limit != null) {limitString = startIndex + " , " + limit;}Condition condition = new Condition(map);Cursor cursor = mSqLiteDatabase.query(mTableName, null, condition.whereCause, condition.whereArgs, null, null, orderBy, limitString);List<T> result = getResult(cursor, where);cursor.close();return result;}