Question

对于我的应用程序，我需要在我的数据库中创建2个不同的表，我的问题是始终只创建了一个表。

这是DatabaseHelper类的核心： -

public class DatabaseHelper extends SQLiteOpenHelper {

    public static final String DATABASE_NAME = "Stundenplan.db";
    public static final String TABLE_NAME = "Fach_table";
    public static final String FACH_ID = "ID";
    public static final String FACH_NAME = "FACHNAME";
    public static final String FACH_KUERZEL = "FACHKUERZEL";
    public static final String FACH_RAUM = "FACHRAUM";
    public static final String FACH_LEHRER = "FACHLEHRER";
    public static final String FACH_FARBE = "FACHFARBE";
    public static final String TABLE_LEHRER = "Lehrer_table";
    public static final String LEHRERID = "ID_L";
    public static final String LEHRERNAME = "LEHRERNAME";
    public static final String LEHRERKUERZEL = "LEHRERKUERZEL";
    public static final String LEHRERRAUM = "LEHRERRAUM";
    public static final String LEHRERMAIL = "LEHRERMAIL";

    private static final String create_Table2 = "create table " + TABLE_LEHRER + "("+ LEHRERID +"INTEGER PRIMARY KEY," + LEHRERNAME +"TEXT," + LEHRERKUERZEL + "TEXT,"+ LEHRERRAUM + "TEXT," + LEHRERMAIL + "TEXT)";
    private static final String create_Table =  "create table " + TABLE_NAME + "("+ FACH_ID + "INTEGER PRIMARY KEY," + FACH_NAME +"TEXT," + FACH_KUERZEL + " TEXT,"+ FACH_RAUM + "TEXT," + FACH_LEHRER + " TEXT)";

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, 1);

        Log.d("MeineAPP", "DB angelegt");
    }

    @Override
    public void onCreate(SQLiteDatabase db) {

        Log.d("MeineAPP", "Tabelle angelegt");
        //  db.execSQL("create table " + TABLE_NAME + "(ID INTEGER PRIMARY KEY AUTOINCREMENT, FACHNAME TEXT, FACHKUERZEL TEXT, FACHRAUM TEXT, FACHLEHRER TEXT)");
        db.execSQL(create_Table);
        db.execSQL(create_Table2);

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int i, int i1) {

        // db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME );
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
        db.execSQL( "DROP TABLE IF EXISTS " + TABLE_LEHRER);

        onCreate(db);
        Log.d("MeineAPP", "in upgrade");

    }
...........   
}

请帮忙！

Answer 1

您的问题“始终只创建了一个表”，这是由于 onCreate 方法在 DatabaseHelper.java 中的常见误解（通常称为数据库助手）每次运行应用程序时都会运行。实际上，onCreate方法仅在数据库的生命周期内自动调用一次。

如果数据库中保存的数据可能丢失，那么修复就是删除数据库。

这可以通过任何一种方式完成
- 从设置/应用或
- 从设置/应用中卸载应用然后，当重新运行应用程序时，将调用onCreate方法。

在您的情况下，onUpgrade删除表（如果存在），然后调用onCreate方法。作为删除应用程序数据/卸载应用程序的替代方法，将增加数据库版本，这将导致运行onUpgrade方法，从而重新创建表。

注意这仍然会导致任何现有数据丢失。

e.g。： -

public DatabaseHelper(Context context) {
    super(context, DATABASE_NAME, null, 2); //<<<< CHANGED 1 to 2
    Log.d("MeineAPP", "DB angelegt");
}

测试您的代码

实际的表创建语句工作并使用logDatabaseInfo from this清理运行产生： -

05-26 20:52:24.618 1398-1398/? D/MeineAPP: DB angelegt
05-26 20:52:24.622 1398-1398/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/jannikokan.de.stundenplan/databases/Stundenplan.db
    Database Version = 1
    Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
05-26 20:52:24.626 1398-1398/? D/SQLITE_CSU: Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table Name = Fach_table Created Using = CREATE TABLE Fach_table(IDINTEGER PRIMARY KEY,FACHNAMETEXT,FACHKUERZEL TEXT,FACHRAUMTEXT,FACHLEHRER TEXT)
    Table = Fach_table ColumnName = IDINTEGER ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 1
    Table = Fach_table ColumnName = FACHNAMETEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHKUERZEL ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHRAUMTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHLEHRER ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table Name = Lehrer_table Created Using = CREATE TABLE Lehrer_table(ID_LINTEGER PRIMARY KEY,LEHRERNAMETEXT,LEHRERKUERZELTEXT,LEHRERRAUMTEXT,LEHRERMAILTEXT)
    Table = Lehrer_table ColumnName = ID_LINTEGER ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 1
    Table = Lehrer_table ColumnName = LEHRERNAMETEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERKUERZELTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERRAUMTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERMAILTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0

但是，查看代码时，您确实遇到了两个方法（zeigeFaecher和zeigeLehrer）的问题，因为您在 * 之间省略了空格并且 from 即您 *from 应该 * from 。

注意 测试仅限于此问题，并且测试绝不是说没有其他方面会导致或不会导致的问题。

附加 - 保留数据（简单解决方案）

如果您需要保存数据，则必须设计一种保存数据的方法。

这可以像添加检查一样简单，以查看预期的表是否存在，如果不存在，例如您可以在Databasehelper.java中添加/添加以下内容： -

e.g。： -

// This is the publicly accessible driver that has the core lists
// i.e. the list of tables that should exist and the
// corresponding table create statements which are passed to
// the createTablesThatDoNotExist method
public void addAnyNewTables() {
    String[] required_tables = new String[]{
            TABLE_NAME,
            TABLE_LEHRER
    };

    String[] table_create_statements = new String[] {
      create_Table,
      create_Table2
    };
    createTablesThatDoNotExist(required_tables,table_create_statements);
}


// This method checks the validity lengths and count of the 2 arrays
// loping through them if valid pass the table and the create statement to the
// doCheckAndCreateOfTable method.
private void createTablesThatDoNotExist(String[] required_tables, String[] table_create_statements) {

    // If no tables or table create statements then finish
    if (required_tables.length < 1 || table_create_statements.length < 1) {
        return;
    }
    // elements in arrays must match
    if (required_tables.length != table_create_statements.length) {
        return;
    }
    SQLiteDatabase db = this.getWritableDatabase();
    String whereclause = "name";
    for (int i=0; i < required_tables.length;i++) {
        if (required_tables[i].length() > 0 && table_create_statements[i].length() > 0) {
            doCheckAndCreateOfTable(
                    required_tables[i].toString(),
                    table_create_statements[i].toString()
            );
        }
    }
}

// This does the real work by interrogatin sqlite_master to see if the table
// exists. If not then it runs the query to create the table using the
// create_statement passed.
private void doCheckAndCreateOfTable(String table,String create_statement) {
    SQLiteDatabase db = this.getWritableDatabase();
    String whereclause = "name=? AND type=?";
    String[] whereargs = new String[]{table,"table"};
    String table_to_query = "sqlite_master";
    Cursor csr = db.query(table_to_query,null,whereclause,whereargs,null,null,null);
    if (csr.getCount() < 1) {
        db.execSQL(create_statement);
    }
    csr.close();
}

然后，您可以在获取DatabaseHelper的实例后在初始活动中调用此方法，例如： -

    mDBHlpr = new DatabaseHelper(this);
    mDBHlpr.addAnyNewTables();
    SQLiteDatabase db = mDBHlpr.getWritableDatabase();
    CommonSQLiteUtilities.logDatabaseInfo(db);

通过注释第二个表的创建，删除应用程序的数据（以及数据库），然后使用onCreate中的以下内容运行应用程序来测试以上内容（故意不创建第二个表））

public void onCreate(SQLiteDatabase db) {

    Log.d("MeineAPP", "Tabelle angelegt");
    //  db.execSQL("create table " + TABLE_NAME + "(ID INTEGER PRIMARY KEY AUTOINCREMENT, FACHNAME TEXT, FACHKUERZEL TEXT, FACHRAUM TEXT, FACHLEHRER TEXT)");
    db.execSQL(create_Table);
    //db.execSQL(create_Table2); //<<<< COMMENTED OUT FOR TEST

}

结果输出为： -

05-26 21:16:07.672 1742-1742/? D/MeineAPP: DB angelegt
05-26 21:16:07.672 1742-1744/? D/dalvikvm: GC_CONCURRENT freed 236K, 10% free 6158K/6791K, paused 11ms+0ms, total 15ms
05-26 21:16:07.708 1742-1742/? D/SQLITE_CSU: DatabaseList Row 1 Name=main File=/data/data/jannikokan.de.stundenplan/databases/Stundenplan.db
    Database Version = 1
    Table Name = android_metadata Created Using = CREATE TABLE android_metadata (locale TEXT)
    Table = android_metadata ColumnName = locale ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table Name = Fach_table Created Using = CREATE TABLE Fach_table(IDINTEGER PRIMARY KEY,FACHNAMETEXT,FACHKUERZEL TEXT,FACHRAUMTEXT,FACHLEHRER TEXT)
    Table = Fach_table ColumnName = IDINTEGER ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 1
    Table = Fach_table ColumnName = FACHNAMETEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHKUERZEL ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHRAUMTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Fach_table ColumnName = FACHLEHRER ColumnType = TEXT Default Value = null PRIMARY KEY SEQUENCE = 0
    Table Name = Lehrer_table Created Using = CREATE TABLE Lehrer_table(ID_LINTEGER PRIMARY KEY,LEHRERNAMETEXT,LEHRERKUERZELTEXT,LEHRERRAUMTEXT,LEHRERMAILTEXT)
    Table = Lehrer_table ColumnName = ID_LINTEGER ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 1
    Table = Lehrer_table ColumnName = LEHRERNAMETEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERKUERZELTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERRAUMTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0
    Table = Lehrer_table ColumnName = LEHRERMAILTEXT ColumnType =  Default Value = null PRIMARY KEY SEQUENCE = 0

<强>即。两个表都已创建

创建多个表并将数据插入其中

1 个答案:

测试您的代码

附加 - 保留数据（简单解决方案）