GreenDao源碼簡要分析
1绿饵、AbstractDaoMaster抽象類的作用
AbstractDaoMaster 的主要作用為：
SQLiteDatabase相關(guān)操作： 所有Table 的創(chuàng)建技掏、刪除隙轻、升級
AbstractDao的信息獲取和存儲： AbstractDao主要作用就是提供操作Table的各種接口
AbstractDaoSession的創(chuàng)建 ：創(chuàng)建AbstractDao犁功，提供簡單的操作表的接口
1.1、SQLiteDatabase的相關(guān)操作
Table的創(chuàng)建臼婆，刪除宜咒，升級操作，是在AbstractDaoMaster子類DaoMaster里面實(shí)現(xiàn)的赘娄，代碼很簡單仆潮，不做過多解釋，相關(guān)代碼如下：
public static void createAllTables(SQLiteDatabase db, boolean ifNotExists) {
NoteDao.createTable(db, ifNotExists);
}
public static void dropAllTables(SQLiteDatabase db, boolean ifExists) {
NoteDao.dropTable(db, ifExists);
}
public static class DevOpenHelper extends OpenHelper {
public DevOpenHelper(Context context, String name, CursorFactory factory) {
super(context, name, factory);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
Log.i("greenDAO", "Upgrading schema from version " + oldVersion + " to " + newVersion + " by dropping all tables");
dropAllTables(db, true);
onCreate(db);
}
}
1.2 AbstractDao的信息獲取和存儲
public DaoMaster(SQLiteDatabase db) {
super(db, SCHEMA_VERSION);
registerDaoClass(NoteDao.class);
}
protected void registerDaoClass(Class<? extends AbstractDao<?, ?>> daoClass) {
DaoConfig daoConfig = new DaoConfig(db, daoClass);
daoConfigMap.put(daoClass, daoConfig);
}
每個AbstractDao對應(yīng)著一個DaoConfig遣臼，然后保存在Map< Class<? extends AbstractDao<?, ?>>, DaoConfig> daoConfigMap中性置，DaoConfig這個類的作用，一是通過反射的方式獲取到AbstractDao對應(yīng)的表名揍堰、表中所有字段（主鍵蚌讼、非主鍵greendao中用Property對象來保存一個字段的信息）等相關(guān)信息辟灰，然后利用這些信息創(chuàng)建了輔助類TableStatements的一個實(shí)例，TableStatements這個類的作用是創(chuàng)建操作table的SQL語句篡石；二是獲取該表對應(yīng)的緩存處理實(shí)例。DaoConfig 和TableStatements 的相關(guān)代碼都很簡單西采，這里不再貼出來了凰萨。
1.3 AbstractDaoSession：創(chuàng)建AbstractDao，提供簡單的操作表的接口
AbstractDaoSession的作用械馆，一是提供獲取AbstractDao的接口胖眷，從而操作各個表：
DevOpenHelper helper = new DaoMaster.DevOpenHelper(this, "notes-db", null);
db = helper.getWritableDatabase();
daoMaster = new DaoMaster(db);
daoSession = daoMaster.newSession();
noteDao = daoSession.getNoteDao();
這里為啥子要通過AbstractDaoSession來創(chuàng)建AbstractDao然后提供給client端使用，而不是直接在AbstractDaoMaster創(chuàng)建出AbstractDao然后提供給client端使用呢霹崎？看AbstractDaoSession里面也提供了操作數(shù)據(jù)庫的簡單接口（當(dāng)然最終都是通過對應(yīng)的AbstractDao來完成的）珊搀，難道就為了這個玩意？尾菇？境析？？派诬？
2劳淆、table操作
理清了關(guān)鍵幾個類的作用后，下面分析table的相關(guān)操作就比較簡單了默赂。
2.1 insert 操作
通過DaoConfig獲取到TableStatements沛鸵，然后由TableStatements得到SQLiteStatement
public long insert(T entity) {// statements = config.statements;
return executeInsert(entity, statements.getInsertStatement());
}
public SQLiteStatement getInsertStatement() {
if (insertStatement == null) {
String sql = SqlUtils.createSqlInsert("INSERT INTO ", tablename, allColumns);
insertStatement = db.compileStatement(sql);
}
return insertStatement;
}
根據(jù)表名、字段生成一條SQL語句
public static String createSqlInsert(String insertInto, String tablename, String[] columns) {
StringBuilder builder = new StringBuilder(insertInto);
builder.append('"').append(tablename).append('"').append(" (");
appendColumns(builder, columns);
builder.append(") VALUES (");
appendPlaceholders(builder, columns.length);
builder.append(')');
return builder.toString();
}
執(zhí)行insert操作
private long executeInsert(T entity, SQLiteStatement stmt) {
long rowId;
if (db.isDbLockedByCurrentThread()) {// database被當(dāng)前線程給鎖住了
synchronized (stmt) {
bindValues(stmt, entity);
rowId = stmt.executeInsert();
}
} else {
// Do TX to acquire a connection before locking the stmt to avoid deadlocks
db.beginTransaction();
try {
synchronized (stmt) {
bindValues(stmt, entity);
rowId = stmt.executeInsert();
}
db.setTransactionSuccessful();
} finally {
db.endTransaction();
}
}
updateKeyAfterInsertAndAttach(entity, rowId, true);
return rowId;
}
給操作的bean更新字段_id的值
protected void updateKeyAfterInsertAndAttach(T entity, long rowId, boolean lock) {
if (rowId != -1) {
K key = updateKeyAfterInsert(entity, rowId);
attachEntity(key, entity, lock);
} else {
// TODO When does this actually happen? Should we throw instead?
DaoLog.w("Could not insert row (executeInsert returned -1)");
}
}
緩存操作：IdentityScope鍵值對缆八，key為表中主鍵曲掰，value為bean
protected final void attachEntity(K key, T entity, boolean lock) {
attachEntity(entity);
if (identityScope != null && key != null) {
if (lock) {
identityScope.put(key, entity);
} else {
identityScope.putNoLock(key, entity);
}
}
}
2.2 query操作
public T load(K key) {
assertSinglePk();
if (key == null) {
return null;
}
if (identityScope != null) {// 如果有緩存，直接從緩存中取值
T entity = identityScope.get(key);
if (entity != null) {
return entity;
}
}
String sql = statements.getSelectByKey();
String[] keyArray = new String[] { key.toString() };
Cursor cursor = db.rawQuery(sql, keyArray);
return loadUniqueAndCloseCursor(cursor);
}
