Question

我正在尝试使用SQLiteOpenHelper将多个表存储到数据库中。我想出了这个共同的基类。

public abstract class BaseHelper<T> extends SQLiteOpenHelper {

private static final int DATABASE_VERSION = 5;
// Database Name
private static final String DATABASE_NAME = "helperdb";

public BaseHelper(Context context) {
    super(context, DATABASE_NAME, null, DATABASE_VERSION);
}

// TODO: Add Java docs here
public abstract String getTableName();

public abstract String getCreateQuery();

public abstract ContentValues getValues(T item);

public abstract T get(Object... id);

public abstract T create(Cursor cursor);

public abstract int update(T item);

public abstract void delete(T item);

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL(getCreateQuery());
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w(PlayerHelper.class.getName(), "Upgrading database from version "
            + oldVersion + " to " + newVersion
            + ", which will destroy all old data");
    db.execSQL(getUpdateQuery());
    onCreate(db);
}

public String getUpdateQuery() {
    // TODO Auto-generated method stub
    StringBuilder sb = new StringBuilder();
    sb.append("DROP TABLE IF EXISTS ");
    sb.append(getTableName());
    return sb.toString();
}

public List<T> getAll() {
    List<T> itemList = new ArrayList<T>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + getTableName();

    SQLiteDatabase db = this.getWritableDatabase();
    Cursor cursor = db.rawQuery(selectQuery, null);

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            T item = create(cursor);
            itemList.add(item);
        } while (cursor.moveToNext());
    }

    return itemList;
}

// Getting contacts Count
public int getCount() {
    String countQuery = "SELECT  * FROM " + getTableName();
    SQLiteDatabase db = this.getReadableDatabase();
    Cursor cursor = db.rawQuery(countQuery, null);
    cursor.close();

    // return count
    return cursor.getCount();
}

public void add(T item) {
    SQLiteDatabase db = this.getWritableDatabase();
    // Inserting Row
    db.insert(getTableName(), null, getValues(item));
    db.close(); // Closing database connection
}
}

然后我在这里有多个实现是1的例子。

public class TeamHelper extends BaseHelper<Team> {

private static final String TABLE_NAME = "teams";

public TeamHelper(Context context) {
    super(context);
}

@Override
public String getCreateQuery() {
    StringBuilder creator = new StringBuilder();
    creator.append("CREATE TABLE ").append(getTableName()).append("(");
    for (Team.SQLValues v : Team.SQLValues.values()) {
        creator.append(v.toString()).append(" ")
                .append(Team.SQLValues.getType(v)).append(", ");
    }
    return creator.substring(0, creator.length() - 2) + ")";
}

@Override
public String getTableName() {
    // TODO Auto-generated method stub
    return TABLE_NAME;
}

/**
 * All CRUD(Create, Read, Update, Delete) Operations
 */

// Adding new contact
@Override
public ContentValues getValues(Team item) {
    ContentValues values = new ContentValues();

    for (Team.SQLValues v : Team.SQLValues.values()) {
        switch (v) {
        case TEAM_ID:
            values.put(v.toString(), Long.toString(item.getTeamId()));
            break;
        case TEAM_NAME:
            values.put(v.toString(), item.getTeamName());
            break;
        case RANK:
            values.put(v.toString(), item.getRank());
            break;
        default:
            break;
        }
    }
    return values;
}

@Override
// Getting single contact
public Team get(Object... id) {
    if(id.length != 1){
        return null;
    }
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_NAME,
            new String[] { Team.SQLValues.TEAM_ID.toString(),
                    Team.SQLValues.TEAM_NAME.toString(),
                    Team.SQLValues.TOTALPOINTS.toString() },
            Team.SQLValues.TEAM_ID.toString() + "=?",
            new String[] { String.valueOf(id[0]) }, null, null, null, null);
    if (cursor != null)
        cursor.moveToFirst();
    return create(cursor);
}

public Team create(Cursor cursor) {
    Team contact = new Team();
    contact.setTeamId(Long.parseLong(cursor.getString(0)));
    contact.setTeamName(cursor.getString(1));
    contact.setTotalPoints(Integer.parseInt(cursor.getString(2)));
    return contact;
}

// Updating single contact
@Override
public int update(Team contact) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(Team.SQLValues.TEAM_NAME.toString(), contact.getTeamName());
    // values.put(KEY_PH_NO, contact.getPhoneNumber());

    // updating row
    return db.update(TABLE_NAME, values, Team.SQLValues.TEAM_ID.toString()
            + " = ?", new String[] { String.valueOf(contact.getTeamId()) });
}

// Deleting single contact
@Override
public void delete(Team contact) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_NAME, Team.SQLValues.TEAM_ID.toString() + " = ?",
            new String[] { String.valueOf(contact.getTeamId()) });
    db.close();
}



}

然后我在活动中单独调用这些SQLLiteHelper ......

public static List<Team> getTeams(Context c) {
    TeamHelper db = new TeamHelper(c);
    return db.getAll();
}

public static List<Player> getPlayers(Context x){
    PlayerHelper h = new PlayerHelper(x);
    return h.getAll();
}

public static List<PlayerTeam> getPlayerTeams(Context x){
    PlayerTeamHelper h = new PlayerTeamHelper(x);
    return h.getAll();
}

List<Team> t = LoginTask.getTeams(this);
List<Player> t2 = LoginTask.getPlayers(this);       
List<PlayerTeam> t3 = LoginTask.getPlayerTeams(this);

这里的问题是第一个工作正常，第二个和第三个说没有匹配的表。如果我改变顺序，那么有效的表也会改变。谁能看到我做错了什么？你能不能拥有一个以上的助手吗？

Answer 1

你似乎过于复杂。每个数据库只需要一个帮助器而不是每个表。

使用多个帮助程序可能会让您遇到各种麻烦，例如数据库锁定异常。这也使得执行多表交易变得非常不可能。

看看我之前发布的这个答案，以获得一种简单易用的数据访问方式。

Easy database access methods in Android

多个SQLLiteOpenHelpers只在Android上创建第一个表

1 个答案: