Android：SQLite数据库无法创建

Question

我已使用以下代码创建表并将数据插入表中。 该代码仅在select语句位于同一文件内时显示数据。 我注意到/ data / data中没有数据库。 我是否缺少某些东西，或者过程实际上是错误的？ 如果有错，那我该怎么办？

surgicalmstDB =  this.openOrCreateDatabase("surgicalmstDB ", SQLiteDatabase.CREATE_IF_NECESSARY, null);
        surgicalmstDB.setVersion(1);
        surgicalmstDB.setLocale(Locale.getDefault());
        surgicalmstDB.setLockingEnabled(true);
        surgicalmstDB.execSQL("CREATE TABLE IF NOT EXISTS " +
                " instrument " +
               " (id int,instrumnt TEXT, category TEXT, details TEXT);");

surgicalmstDB.execSQL("INSERT INTO " +
                "instrument" +
                " Values (2,'#3 Long Knife Handle ','Cutting and dissecting','Used to cut deeper tissue.');");

//-----------------------------------------------------------------
 String query="SELECT * from instrument WHERE id=2";
                Cursor cursor=surgicalmstDB.rawQuery(query, null);
                while (cursor.moveToNext()) {
                    String title =cursor.getString(cursor
                            .getColumnIndex("instrumnt"));
                    String author= cursor.getString(cursor
                            .getColumnIndex("category"));
                    String price= cursor.getString(cursor
                            .getColumnIndex("details"));
                       txt.setText(title+"-----"+author+"-------"+price);
                    }
                    cursor.close();
                    surgicalmstDB.close();

Answer 1

我建议您引用SQLiteOpenHelper而不是硬编码查询。

以下代码将为您提供帮助

员工模型班

package com.database;

public class Employee {


    int _id;
    String _name;
    String _phone_number;


    public Employee (){

    }
    // constructor
    public Employee (int id, String name, String _phone_number){
        this._id = id;
        this._name = name;
        this._phone_number = _phone_number;
    }

    // constructor
    public Employee (String name, String _phone_number){
        this._name = name;
        this._phone_number = _phone_number;
    }
    // getting ID
    public int getID(){
        return this._id;
    }

    // setting id
    public void setID(int id){
        this._id = id;
    }

    // getting name
    public String getName(){
        return this._name;
    }

    // setting name
    public void setName(String name){
        this._name = name;
    }

    // getting phone number
    public String getPhoneNumber(){
        return this._phone_number;
    }

    // setting phone number
    public void setPhoneNumber(String phone_number){
        this._phone_number = phone_number;
    }
}

SQLite助手类

公共类DatabaseHelper扩展了SQLiteOpenHelper {

  private static final int DATABASE_VERSION = 1;

  private static final String DATABASE_NAME = "employeeDB";


  private static final String TABLE_EMPLOYEE = "employee";


private static final String KEY_ID = "id";
private static final String KEY_NAME = "name";
private static final String KEY_PH_NO = "phone_number";

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

// Creating Tables
@Override
public void onCreate(SQLiteDatabase db) {
    String CREATE_CONTACTS_TABLE = "CREATE TABLE " + TABLE_EMPLOYEE + "("
            + KEY_ID + " INTEGER PRIMARY KEY," + KEY_NAME + " TEXT,"
            + KEY_PH_NO + " TEXT" + ")";
    db.execSQL(CREATE_CONTACTS_TABLE);
}

// Upgrading database
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    // Drop older table if existed
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_CONTACTS);

    // Create tables again
    onCreate(db);
} 

CRUD操作

// 添加新员工

public void addEmployee(Employee employee) {}

// 获得单名员工

public Contact getEmployee(int id) {}

// 获取所有员工

public List<Employee> getAllEmployees() {}

// 让员工计数

public int getEmployeesCount() {}

// 更新单个员工

public int updateEmployee(Employee employee) {}

// 删除单个员工

public void deleteEmployee(Employee employee) {}

插入新记录

public void addemployee(Employee employee) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, employee.getName()); 
    values.put(KEY_PH_NO, employee.getPhoneNumber()); 
    db.insert(TABLE_EMPLOYEE, null, values);
    db.close();
}

读取行

public Contact getEmployee(int id) {
    SQLiteDatabase db = this.getReadableDatabase();

    Cursor cursor = db.query(TABLE_EMPLOYEE, new String[] { KEY_ID,
            KEY_NAME, KEY_PH_NO }, KEY_ID + "=?",
            new String[] { String.valueOf(id) }, null, null, null, null);
    if (cursor != null)
        cursor.moveToFirst();

    Employee employee= new Employee(Integer.parseInt(cursor.getString(0)),
            cursor.getString(1), cursor.getString(2));

    return employee;
}

招募所有员工

public List<Contact> getAllEmployees() {
    List<Employee> employeeList = new ArrayList<Employee>();
    // Select All Query
    String selectQuery = "SELECT  * FROM " + TABLE_EMPLOYEE;

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

    // looping through all rows and adding to list
    if (cursor.moveToFirst()) {
        do {
            Employee employee= new Employee();
            employee.setID(Integer.parseInt(cursor.getString(0)));
            employee.setName(cursor.getString(1));
            employee.setPhoneNumber(cursor.getString(2));

            employeeList.add(employee);
        } while (cursor.moveToNext());
    }

       return employeeList;
}

让所有员工计数

 public int getEmployeesCount() {
        String countQuery = "SELECT  * FROM " + TABLE_EMPLOYEE;
        SQLiteDatabase db = this.getReadableDatabase();
        Cursor cursor = db.rawQuery(countQuery, null);
        cursor.close();

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

更新记录

public int updateEmployee(Employee employee) {
    SQLiteDatabase db = this.getWritableDatabase();

    ContentValues values = new ContentValues();
    values.put(KEY_NAME, employee.getName());
    values.put(KEY_PH_NO, employee.getPhoneNumber());

    // updating row
    return db.update(TABLE_EMPLOYEE, values, KEY_ID + " = ?",
            new String[] { String.valueOf(employee.getID()) });
}

删除记录

public void deleteEmployee(Employee employee) {
    SQLiteDatabase db = this.getWritableDatabase();
    db.delete(TABLE_EMPLOYEE, KEY_ID + " = ?",
            new String[] { String.valueOf(employee.getID()) });
    db.close();
}