Android ORMLite ForeignCollection关联外部集合

亦凉 2023-10-16 21:52 4阅读 0赞

《Android ORMLite ForeignCollection关联外部集合》  
  
Android ORMLite ForeignCollection关联外部集合的功能，适合层级比较深，数据模型互相渗透、交叉的数据结构或集合。尤其方便解决复杂数据模型。简单期间，我们暂时以 班级 <-> 学生 这样的数据模型为例加以说明。一个班级里面有若干学生(一对多，1<-n)，反过来说，若干个学生集合到一个班级中（n->1）。 在Android ORMLite中，这样的结构模型可以用@ForeignCollectionField，ForeignCollection建模。我们定义一个班级类AClass（之所以在 'Class'前加一个‘A’，是因为Java语言中，'Class'是保留字，却刚好是我们想用的班级英文单词，真不巧，所以前面加个'A'规避），AClass包含id（主键，方便查询和更新），name以及指向一个外部Student的集合（ForeignCollection<Student>）。同样，我们定义学生类Student，Student中埋入一个字段aclass指向外部的AClass。  
  
备注：  
Android ORMLite简介文章：[http://blog.csdn.net/zhangphil/article/details/46878075][http_blog.csdn.net_zhangphil_article_details_46878075]  
  
示例代码总共有4个文件：MainActivity.java，主Activity，用于测试。ORMLiteDatabaseHelper.java , AClass.java , Student.java 是数据库相关的代码文件，用于建模。

结构层次如图：

![Center][]

测试用的MainActivity.java :

package zhangphil.ormlitetest;
    
    import java.sql.SQLException;
    
    import com.j256.ormlite.dao.Dao;
    import com.j256.ormlite.dao.ForeignCollection;
    
    import zhangphil.ormlitetest.database.AClass;
    import zhangphil.ormlitetest.database.ORMLiteDatabaseHelper;
    import zhangphil.ormlitetest.database.Student;
    import android.support.v7.app.ActionBarActivity;
    import android.widget.Toast;
    import android.os.Bundle;
    
    public class MainActivity extends ActionBarActivity {
    
    	private Dao<AClass, Integer> mClassDao;
    	private Dao<Student, Integer> mStudentDao;
    
    	@Override
    	protected void onCreate(Bundle savedInstanceState) {
    		super.onCreate(savedInstanceState);
    
    		ORMLiteDatabaseHelper mDatabaseHelper = ORMLiteDatabaseHelper
    				.getInstance(this);
    
    		mClassDao = mDatabaseHelper.getClassDao();
    		mStudentDao = mDatabaseHelper.getStudentDao();
    
    		// 创建5个班级用以演示。
    		for (int i = 1; i < 6; i++) {
    			AClass aclass = new AClass();
    			aclass.id = i;
    			aclass.name = i + "班";
    			try {
    				mClassDao.createIfNotExists(aclass);
    			} catch (SQLException e) {
    				e.printStackTrace();
    			}
    		}
    
    		// 找到id=1的1班。
    		AClass class1 = null;
    		try {
    			class1 = mClassDao.queryForId(1);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    
    		// 创建19个学生，这19个学生都归属到1班。
    		for (int i = 1; i < 20; i++) {
    			Student s = new Student();
    			s.id = i;
    			s.name = "学生" + i;
    
    			// 将新创建的这些学生所在班级指针指向1班。
    			// 数据模型：id=1的1班和这19个学生是1对多的学生，换句话说，这19个学生是1班的学生。
    			s.aclass = class1;
    
    			try {
    				mStudentDao.createIfNotExists(s);
    			} catch (SQLException e) {
    				e.printStackTrace();
    			}
    		}
    	}
    
    	@Override
    	public void onStart() {
    		super.onStart();
    
    		/**
    		 * 下面我们演示更新一个Student的信息， 然后向上，依据外键，从Student - > Class更新班级信息。
    		 * 
    		 * */
    
    		// 假设我们更新其中id=1的这个学生所在的这个班级的name变成“一班”。
    		Student s1 = null;
    		try {
    			s1 = mStudentDao.queryForId(1);
    
    			s1.aclass.name = "一班";
    
    			// 更新1班的名字从“1班”变成“一班”
    			mClassDao.update(s1.aclass);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    
    		// 显示我们更新后的结果。
    		AClass class1 = null;
    		try {
    			class1 = mClassDao.queryForId(1);
    		} catch (SQLException e1) {
    			e1.printStackTrace();
    		}
    
    		ForeignCollection<Student> students = class1.students;
    		for (Student s : students) {
    			Toast.makeText(this, s.toString(), Toast.LENGTH_SHORT).show();
    		}
    	}
    }

以下是数据库相关的建模：

AClass.java :

package zhangphil.ormlitetest.database;
    
    import com.j256.ormlite.dao.ForeignCollection;
    import com.j256.ormlite.field.DataType;
    import com.j256.ormlite.field.DatabaseField;
    import com.j256.ormlite.field.ForeignCollectionField;
    import com.j256.ormlite.table.DatabaseTable;
    
    @DatabaseTable(tableName = "classes")
    public class AClass {
    
    	@DatabaseField(canBeNull = false, dataType = DataType.LONG, id = true)
    	public long id;
    
    	@DatabaseField(canBeNull = false, defaultValue = "a class", dataType = DataType.STRING)
    	public String name;
    
    	@ForeignCollectionField(eager = false)
    	public ForeignCollection<Student> students = null;
    
    	public AClass() {
    
    	}
    }

Student.java :

package zhangphil.ormlitetest.database;
    
    import com.j256.ormlite.field.DataType;
    import com.j256.ormlite.field.DatabaseField;
    import com.j256.ormlite.table.DatabaseTable;
    
    @DatabaseTable(tableName = "students")
    public class Student {
    
    	public Student(String name, int student_id) {
    		this.name = name;
    		this.id = student_id;
    	}
    
    	@DatabaseField(canBeNull = false, dataType = DataType.INTEGER, id = true)
    	public int id;
    
    	@DatabaseField(canBeNull = false, dataType = DataType.STRING)
    	public String name;
    
    	@DatabaseField(canBeNull = false, foreign = true, foreignAutoRefresh = true)
    	public AClass aclass;
    
    	public Student() {
    
    	}
    
    	@Override
    	public String toString() {
    		return "id:" + id + " 姓名:" + name + " 所在班级:" + aclass.name;
    	}
    }

ORMLiteDatabaseHelper.java :

package zhangphil.ormlitetest.database;
    
    import java.sql.SQLException;
    
    import android.content.Context;
    import android.database.sqlite.SQLiteDatabase;
    import android.database.sqlite.SQLiteDatabase.CursorFactory;
    import android.util.Log;
    
    import com.j256.ormlite.android.apptools.OrmLiteSqliteOpenHelper;
    import com.j256.ormlite.dao.Dao;
    import com.j256.ormlite.support.ConnectionSource;
    import com.j256.ormlite.table.TableUtils;
    
    public class ORMLiteDatabaseHelper extends OrmLiteSqliteOpenHelper {
    
    	private static ORMLiteDatabaseHelper mDatabaseHelper = null;
    
    	private Dao<AClass, Integer> mClassDao = null;
    	private Dao<Student, Integer> mStudentDao = null;
    
    	private final static String DataBase_NAME = "school.db";
    	private final static int DataBase_VERSION = 1;
    
    	public ORMLiteDatabaseHelper(Context context, String databaseName,
    			CursorFactory factory, int databaseVersion) {
    		super(context, DataBase_NAME, factory, DataBase_VERSION);
    	}
    
    	public static ORMLiteDatabaseHelper getInstance(Context context) {
    		if (mDatabaseHelper == null) {
    			mDatabaseHelper = new ORMLiteDatabaseHelper(context, DataBase_NAME,
    					null, DataBase_VERSION);
    		}
    
    		return mDatabaseHelper;
    	}
    
    	@Override
    	public void onCreate(SQLiteDatabase arg0, ConnectionSource connectionSource) {
    
    		Log.d(this.getClass().getName(), "ORMLite数据库 -> onCreate");
    
    		try {
    			TableUtils.createTableIfNotExists(connectionSource, AClass.class);
    			TableUtils.createTableIfNotExists(connectionSource, Student.class);
    		} catch (Exception e) {
    			e.printStackTrace();
    		}
    	}
    
    	@Override
    	public void onUpgrade(SQLiteDatabase database,
    			ConnectionSource connectionSource, int oldVersion, int newVersion) {
    
    		Log.i(this.getClass().getName(), "数据库 -> onUpgrade");
    
    		try {
    			// 删除旧的数据库表。
    			TableUtils.dropTable(connectionSource, AClass.class, true);
    			TableUtils.dropTable(connectionSource, Student.class, true);
    
    			// 重新创建新版的数据库。
    			onCreate(database, connectionSource);
    		} catch (SQLException e) {
    			e.printStackTrace();
    		}
    	}
    
    	public Dao<Student, Integer> getStudentDao() {
    		if (mStudentDao == null) {
    			try {
    				mStudentDao = getDao(Student.class);
    			} catch (java.sql.SQLException e) {
    				e.printStackTrace();
    			}
    		}
    
    		return mStudentDao;
    	}
    
    	public Dao<AClass, Integer> getClassDao() {
    		if (mClassDao == null) {
    			try {
    				mClassDao = getDao(AClass.class);
    			} catch (java.sql.SQLException e) {
    				e.printStackTrace();
    			}
    		}
    
    		return mClassDao;
    	}
    
    	@Override
    	public void close() {
    		super.close();
    		mClassDao = null;
    		mStudentDao = null;
    	}
    }

[http_blog.csdn.net_zhangphil_article_details_46878075]: http://blog.csdn.net/zhangphil/article/details/46878075
[Center]: https://img-blog.csdn.net/20150715114445590?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center