Android ORMLite ForeignCollection关联外部集合

丈夫欲遂平生志，一载寒窗一举汤。这篇文章主要讲述Android ORMLite ForeignCollection关联外部集合相关的知识，希望能为你提供帮助。
??《android ORMLite ForeignCollection关联外部集合》

Android ORMLite ForeignCollection关联外部集合的功能，适合层级比較深，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，我们临时以班级 < -> 学生这种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。这种结构模型能够用@ForeignCollectionField。ForeignCollection建模。我们定义一个班级类AClass（之所以在 ‘Class‘前加一个‘A’，是由于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，所曾经面加个‘A‘规避）。AClass包括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> ）。
相同。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简单介绍文章：http://blog.csdn.net/zhangphil/article/details/46878075

演示样例代码总共同拥有4个文件：MainActivity.java，主Activity，用于測试。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：

文章图片

測试用的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(); /** * 以下我们演示更新一个Student的信息，然后向上，根据外键，从Student - > Class更新班级信息。 * * */// 如果我们更新当中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(); } } }

下面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 = "https://www.songbingjia.com/android/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); // 又一次创建新版的数据库。 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; } }

【Android ORMLite ForeignCollection关联外部集合】