Improving Android ORMLite foreign key mapping , based on new version 5.0

秒速五厘米 2024-02-18 16:54 6阅读 0赞

**Improving Android ORMLite foreign key mapping , based on new version 5.0**

AClass.java：

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(generatedId = true)
        public int id;
    
        @DatabaseField(canBeNull = false, dataType = DataType.INTEGER)
        public int classId;
    
        @DatabaseField(canBeNull = false, defaultValue = "class", dataType = DataType.STRING)
        public String name;
    
        @ForeignCollectionField(eager = false)
        public ForeignCollection<Student> students;
    
        @Override
        public String toString() {
            return "id:" + id + ",classId:" + classId + ",name:" + name;
        }
    }

Student.java：

import com.j256.ormlite.field.DataType;
    import com.j256.ormlite.field.DatabaseField;
    import com.j256.ormlite.table.DatabaseTable;
    
    @DatabaseTable(tableName = "students")
    public class Student {
        @DatabaseField(generatedId = true)
        public int id;
    
        @DatabaseField(canBeNull = false, dataType = DataType.INTEGER)
        public int studentId;
    
        @DatabaseField(canBeNull = false, dataType = DataType.STRING)
        public String name;
    
        @DatabaseField(canBeNull = false, foreign = true, foreignAutoRefresh = true)
        public AClass aclass;
    
        @Override
        public String toString() {
            return "id:" + id + ",studentId:" + studentId + ",name:" + name + ",className:" + aclass.name;
        }
    }

ORMLiteDatabaseHelper.java：

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 DB_NAME = "school.db";
        private final static int DB_VERSION = 1;
    
        public ORMLiteDatabaseHelper(Context context, String databaseName, CursorFactory factory, int databaseVersion) {
            super(context, DB_NAME, factory, DB_VERSION);
        }
    
        public static ORMLiteDatabaseHelper getInstance(Context context) {
            if (mDatabaseHelper == null) {
                mDatabaseHelper = new ORMLiteDatabaseHelper(context, DB_NAME, null, DB_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;
        }
    }

MainActivity.java：

import java.sql.SQLException;
    
    import com.j256.ormlite.dao.Dao;
    import com.j256.ormlite.dao.ForeignCollection;
    
    import android.support.v7.app.AppCompatActivity;
    import android.util.Log;
    import android.os.Bundle;
    
    public class MainActivity extends AppCompatActivity {
    
        private Dao<AClass, Integer> mClassDao;
        private Dao<Student, Integer> mStudentDao;
    
        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
    
            ORMLiteDatabaseHelper mORMLiteDatabaseHelper = ORMLiteDatabaseHelper.getInstance(getApplicationContext());
    
            mClassDao = mORMLiteDatabaseHelper.getClassDao();
            mStudentDao = mORMLiteDatabaseHelper.getStudentDao();
    
            // 在数据库中存储5个班级。
            for (int i = 1; i < 6; i++) {
                AClass aclass = new AClass();
                aclass.classId = 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10个学生，这10个学生都归属到1班。
            for (int i = 0; i < 10; i++) {
                Student s = new Student();
                s.studentId = 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。
                // 1班有这19个学生，换言之，这19个学生是1班的学生。
                s.aclass = class1;
    
                try {
                    mStudentDao.createIfNotExists(s);
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
    
            ForeignCollection<Student> students = class1.students;
            for (Student s : students) {
                Log.d("数据库", s.toString());
            }
        }
    }