如何在 Android 中更好地安排我的 SQLite 数据库 class
How to better arrange my SQLite database class in Android
我是 Android 开发的新手，我想确保我正在学习做事的体面做法。现在这是我的数据库 class，它目前允许我创建一个新的单例实例，以及创建一个配置文件 table，以及从配置文件 [=] add/retrieve 59=]。
到目前为止，这是我的代码：
public class DatabaseHelper extends SQLiteOpenHelper {
private static volatile SQLiteDatabase mDatabase;
private static DatabaseHelper mInstance = null;
private static Context mContext;
private static final String DB_NAME = "database.db";
private static final int DB_VERSION = 1;
public static final String PROFILES_TABLE = "PROFILES";
public static final String PROFILES_COLUMN_ID = "_ID";
public static final String PROFILES_COLUMN_NAME = "NAME";
private static final String DB_CREATE_PROFILES_TABLE =
"CREATE TABLE " + PROFILES_TABLE + " ("
+ PROFILES_COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ PROFILES_COLUMN_NAME + " TEXT UNIQUE NOT NULL)";
public static synchronized DatabaseHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new DatabaseHelper(context.getApplicationContext());
try {
mInstance.open();
}
catch (SQLException e) {
e.printStackTrace();
}
}
return mInstance;
}
private DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DB_CREATE_PROFILES_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
@Override
public void onConfigure(SQLiteDatabase db){
super.onConfigure(db);
db.setForeignKeyConstraintsEnabled(true);
}
public synchronized void open() throws SQLException {
mDatabase = getWritableDatabase();
}
public synchronized void close() {
mDatabase.close();
}
public synchronized long addNewProfile(String name) {
ContentValues values = new ContentValues();
values.put(DatabaseHelper.PROFILES_COLUMN_NAME, name);
return mDatabase.insertWithOnConflict(DatabaseHelper.PROFILES_TABLE, null, values, SQLiteDatabase.CONFLICT_IGNORE);
}
public synchronized Profile getProfileById(long profileId) {
Cursor cursor = mDatabase.query(
DatabaseHelper.PROFILES_TABLE, // table
new String[]{DatabaseHelper.PROFILES_COLUMN_ID, DatabaseHelper.PROFILES_COLUMN_NAME}, // column names
DatabaseHelper.PROFILES_COLUMN_ID + " = ?", // where clause
new String[]{profileId + ""}, // where params
null, // groupby
null, // having
null); // orderby
cursor.moveToFirst();
Profile profile = null;
if (!cursor.isAfterLast()) {
String profileName = getStringFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_NAME);
profile = new Profile(profileId, profileName);
cursor.moveToNext();
}
cursor.close();
return profile;
}
public synchronized List<Profile> getAllProfiles() {
List<Profile> profiles = new ArrayList<>();
Cursor cursor = mDatabase.query(
DatabaseHelper.PROFILES_TABLE, // table
new String[]{DatabaseHelper.PROFILES_COLUMN_ID, DatabaseHelper.PROFILES_COLUMN_NAME}, // column names
null, // where clause
null, // where params
null, // groupby
null, // having
DatabaseHelper.PROFILES_COLUMN_NAME); // orderby
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
long profileId = getLongFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_ID);
String profileName = getStringFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_NAME);
profiles.add(new Profile(profileId, profileName));
cursor.moveToNext();
}
cursor.close();
return profiles;
}
private synchronized long getLongFromColumnName(Cursor cursor, String columnName) {
int columnIndex = cursor.getColumnIndex(columnName);
return cursor.getLong(columnIndex);
}
private synchronized String getStringFromColumnName(Cursor cursor, String columnName) {
int columnIndex = cursor.getColumnIndex(columnName);
return cursor.getString(columnIndex);
}
}
供参考（这可能是必要的，也可能不是必要的，但我发布它以防万一），我的个人资料 class，这是我在应用程序的其他几个地方使用的内容：
public class Profile {
private long mId;
private String mName;
public Profile(long id, String name) {
mId = id;
mName = name;
}
public long getId() {
return mId;
}
public void setId(long id) {
mId = id;
}
public String getName() {
return mName;
}
public void setName(String name) {
mName = name;
}
}
我的问题：
像这样将 table 的字段名称存储在数据库 class 中是否合适，或者我应该将其移动到它自己的单独 class（例如某种包含所有名称的 ProfileSql class）。
我是否应该以某种方式将 CRUD 查询逻辑与此 class 分离？我该怎么做呢？如果我有多个 table、查询、线程方法等怎么办？这些也都放在它们自己单独的 classes 中吗？如果我为几个 table 添加 CRUD 函数，这个 class 会很快变得非常大。
我是否应该以某种方式将这些东西绑定到我的个人资料 class 本身，我在我的应用程序的其他几个地方使用它？例如，我是否应该在配置文件 class 中包含配置文件 table SQL 内容（创建 table 字符串和 table/column 名称），或者这是在干预不该在一起的东西？
如您所见，我主要是在问东西应该放在哪里。现在我只是将它们全部集中到一个数据库中 class.
我的主要意图：
我希望这个例子足够短，有人可以向我展示重组所有这些的正确方法，这样我就可以掌握这些技能，并在事情变得越来越复杂时应用它们。
您应该将不同的表分成所谓的模型 类。每个模型都有自己的一组数据库函数。
DatabaseHelper（或 DatabaseController）的存在只是为了提供一个 "handle" 来使用。
我没有时间写一个非常详细的答案，但我确实给你写了一些示例代码（可能无法直接编译）。
DatabaseController.java
此控制器还处理多个数据库用户 (Threads) 并启用外键约束（您可能需要这些）。
public final class DatabaseController extends SQLiteOpenHelper {
public static abstract class LocalDatabaseModel {
public LocalDatabaseModel(){
}
public void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion){
}
public abstract void onCreate(SQLiteDatabase database);
}
private SQLiteDatabase database;
private int openConnections = 0;
private static final String DATABASE = "database-name.db";
private static final int VERSION = 1;
private static DatabaseController instance = null;
// Add you LocalDatabaseModels here.
private final LocalDatabaseModel[] models = new LocalDatabaseModel[]{new Book.Model(), new Writer.Model()};
public synchronized static DatabaseController getInstance(Context context) {
if (instance == null) {
instance = new DatabaseController(context.getApplicationContext());
}
return instance;
}
private DatabaseController(Context context) {
super(context, DATABASE, null, VERSION);
}
/**
* Must be called from the same thread as the original openDatabase call.
*/
@Override
public synchronized void close() {
if(database == null || openConnections == 0){
throw new IllegalStateException("Database already closed or has never been opened.");
}
openConnections--;
if(openConnections != 0){
return;
}
database = null;
super.close();
}
/**
* Do not manually call this method! Use openDatabase(), database() and close()!
*
* Opens the SQLiteDatabase if not already opened.
* This implementation does the exact same thing as getWritableDatabase and thus will return a writable database.
*
* @return the newly opened database or the existing database.
*/
@Override
public synchronized SQLiteDatabase getReadableDatabase() {
return getWritableDatabase();
}
/**
*
* Do not manually call this method! Use openDatabase(), database() and close()!
*
* Opens the SQLiteDatabase if not already opened.
*
* @return the newly opened database or the existing database.
*/
@Override
public synchronized SQLiteDatabase getWritableDatabase() {
if(database == null){
database = super.getWritableDatabase();
}
openConnections++;
return database;
}
/**
* Open the database. Always pair this call with close() and use database() to get the opened database!
*/
public synchronized void openDatabase(){
getWritableDatabase();
}
/**
* Returns the opened database. Throws an exception if the database has not been opened yet!
* @return the database.
*/
public synchronized SQLiteDatabase database(){
if(database == null){
throw new IllegalStateException("Database has not been opened yet!");
}
return database;
}
@Override
public synchronized void onCreate(SQLiteDatabase db) {
setForeignKeyConstraintsEnabled(db);
for(LocalDatabaseModel model: models){
model.onCreate(db);
}
}
@Override
public synchronized void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
setForeignKeyConstraintsEnabled(db);
for(LocalDatabaseModel model: models){
model.onUpgrade(db, oldVersion, newVersion);
}
}
@Override
public synchronized void onOpen(SQLiteDatabase db) {
setForeignKeyConstraintsEnabled(db);
}
@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
@Override
public synchronized void onConfigure(SQLiteDatabase db) {
db.setForeignKeyConstraintsEnabled(true);
}
private void setForeignKeyConstraintsEnabled(SQLiteDatabase db){
//Skip for Android 4.1 and newer as this is already handled in onConfigure
if(Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN && !db.isReadOnly()) {
db.execSQL("PRAGMA foreign_keys=ON;");
}
}
/* I often have some utility methods in this class too. */
public long getCount(String table){
return DatabaseUtils.queryNumEntries(database(), table);
}
}
Book.java
public final class Book {
private long id = -1;
private String title;
public Book(String title){
this.title = title;
}
private Book(long id, String title){
this.title = title;
this.id = id;
}
public void save(DatabaseController db){
//save or update the book, throw an exception on failure.
}
//More non static methods (getters, setters, database methods) here
public static Book getById(DatabaseController db, long id){
//Do select query and get an existing book from the database.
}
//More static methods here
public static class Model extends LocalDatabaseModel {
public Model(){
}
@Override
public void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion){
//Implement update logic for this model/table
}
@Override
public void onCreate(SQLiteDatabase database){
//Implement create logic for this model/table
}
}
}
用法
DatabaseController db = DatabaseController.getInstance(context);
db.openDatabase();
Book book = new Book("Alice in Wonderland");
book.save(db);
db.close();
我是 Android 开发的新手，我想确保我正在学习做事的体面做法。现在这是我的数据库 class，它目前允许我创建一个新的单例实例，以及创建一个配置文件 table，以及从配置文件 [=] add/retrieve 59=]。
到目前为止，这是我的代码：
public class DatabaseHelper extends SQLiteOpenHelper {
private static volatile SQLiteDatabase mDatabase;
private static DatabaseHelper mInstance = null;
private static Context mContext;
private static final String DB_NAME = "database.db";
private static final int DB_VERSION = 1;
public static final String PROFILES_TABLE = "PROFILES";
public static final String PROFILES_COLUMN_ID = "_ID";
public static final String PROFILES_COLUMN_NAME = "NAME";
private static final String DB_CREATE_PROFILES_TABLE =
"CREATE TABLE " + PROFILES_TABLE + " ("
+ PROFILES_COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, "
+ PROFILES_COLUMN_NAME + " TEXT UNIQUE NOT NULL)";
public static synchronized DatabaseHelper getInstance(Context context) {
if (mInstance == null) {
mInstance = new DatabaseHelper(context.getApplicationContext());
try {
mInstance.open();
}
catch (SQLException e) {
e.printStackTrace();
}
}
return mInstance;
}
private DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(DB_CREATE_PROFILES_TABLE);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
}
@Override
public void onConfigure(SQLiteDatabase db){
super.onConfigure(db);
db.setForeignKeyConstraintsEnabled(true);
}
public synchronized void open() throws SQLException {
mDatabase = getWritableDatabase();
}
public synchronized void close() {
mDatabase.close();
}
public synchronized long addNewProfile(String name) {
ContentValues values = new ContentValues();
values.put(DatabaseHelper.PROFILES_COLUMN_NAME, name);
return mDatabase.insertWithOnConflict(DatabaseHelper.PROFILES_TABLE, null, values, SQLiteDatabase.CONFLICT_IGNORE);
}
public synchronized Profile getProfileById(long profileId) {
Cursor cursor = mDatabase.query(
DatabaseHelper.PROFILES_TABLE, // table
new String[]{DatabaseHelper.PROFILES_COLUMN_ID, DatabaseHelper.PROFILES_COLUMN_NAME}, // column names
DatabaseHelper.PROFILES_COLUMN_ID + " = ?", // where clause
new String[]{profileId + ""}, // where params
null, // groupby
null, // having
null); // orderby
cursor.moveToFirst();
Profile profile = null;
if (!cursor.isAfterLast()) {
String profileName = getStringFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_NAME);
profile = new Profile(profileId, profileName);
cursor.moveToNext();
}
cursor.close();
return profile;
}
public synchronized List<Profile> getAllProfiles() {
List<Profile> profiles = new ArrayList<>();
Cursor cursor = mDatabase.query(
DatabaseHelper.PROFILES_TABLE, // table
new String[]{DatabaseHelper.PROFILES_COLUMN_ID, DatabaseHelper.PROFILES_COLUMN_NAME}, // column names
null, // where clause
null, // where params
null, // groupby
null, // having
DatabaseHelper.PROFILES_COLUMN_NAME); // orderby
cursor.moveToFirst();
while (!cursor.isAfterLast()) {
long profileId = getLongFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_ID);
String profileName = getStringFromColumnName(cursor, DatabaseHelper.PROFILES_COLUMN_NAME);
profiles.add(new Profile(profileId, profileName));
cursor.moveToNext();
}
cursor.close();
return profiles;
}
private synchronized long getLongFromColumnName(Cursor cursor, String columnName) {
int columnIndex = cursor.getColumnIndex(columnName);
return cursor.getLong(columnIndex);
}
private synchronized String getStringFromColumnName(Cursor cursor, String columnName) {
int columnIndex = cursor.getColumnIndex(columnName);
return cursor.getString(columnIndex);
}
}
供参考（这可能是必要的，也可能不是必要的，但我发布它以防万一），我的个人资料 class，这是我在应用程序的其他几个地方使用的内容：
public class Profile {
private long mId;
private String mName;
public Profile(long id, String name) {
mId = id;
mName = name;
}
public long getId() {
return mId;
}
public void setId(long id) {
mId = id;
}
public String getName() {
return mName;
}
public void setName(String name) {
mName = name;
}
}
我的问题：
像这样将 table 的字段名称存储在数据库 class 中是否合适，或者我应该将其移动到它自己的单独 class（例如某种包含所有名称的
ProfileSqlclass）。我是否应该以某种方式将 CRUD 查询逻辑与此 class 分离？我该怎么做呢？如果我有多个 table、查询、线程方法等怎么办？这些也都放在它们自己单独的 classes 中吗？如果我为几个 table 添加 CRUD 函数，这个 class 会很快变得非常大。
我是否应该以某种方式将这些东西绑定到我的个人资料 class 本身，我在我的应用程序的其他几个地方使用它？例如，我是否应该在配置文件 class 中包含配置文件 table SQL 内容（创建 table 字符串和 table/column 名称），或者这是在干预不该在一起的东西？
如您所见，我主要是在问东西应该放在哪里。现在我只是将它们全部集中到一个数据库中 class.
我的主要意图：
我希望这个例子足够短，有人可以向我展示重组所有这些的正确方法，这样我就可以掌握这些技能，并在事情变得越来越复杂时应用它们。
您应该将不同的表分成所谓的模型 类。每个模型都有自己的一组数据库函数。
DatabaseHelper（或 DatabaseController）的存在只是为了提供一个 "handle" 来使用。
我没有时间写一个非常详细的答案，但我确实给你写了一些示例代码（可能无法直接编译）。
DatabaseController.java
此控制器还处理多个数据库用户 (Threads) 并启用外键约束（您可能需要这些）。
public final class DatabaseController extends SQLiteOpenHelper {
public static abstract class LocalDatabaseModel {
public LocalDatabaseModel(){
}
public void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion){
}
public abstract void onCreate(SQLiteDatabase database);
}
private SQLiteDatabase database;
private int openConnections = 0;
private static final String DATABASE = "database-name.db";
private static final int VERSION = 1;
private static DatabaseController instance = null;
// Add you LocalDatabaseModels here.
private final LocalDatabaseModel[] models = new LocalDatabaseModel[]{new Book.Model(), new Writer.Model()};
public synchronized static DatabaseController getInstance(Context context) {
if (instance == null) {
instance = new DatabaseController(context.getApplicationContext());
}
return instance;
}
private DatabaseController(Context context) {
super(context, DATABASE, null, VERSION);
}
/**
* Must be called from the same thread as the original openDatabase call.
*/
@Override
public synchronized void close() {
if(database == null || openConnections == 0){
throw new IllegalStateException("Database already closed or has never been opened.");
}
openConnections--;
if(openConnections != 0){
return;
}
database = null;
super.close();
}
/**
* Do not manually call this method! Use openDatabase(), database() and close()!
*
* Opens the SQLiteDatabase if not already opened.
* This implementation does the exact same thing as getWritableDatabase and thus will return a writable database.
*
* @return the newly opened database or the existing database.
*/
@Override
public synchronized SQLiteDatabase getReadableDatabase() {
return getWritableDatabase();
}
/**
*
* Do not manually call this method! Use openDatabase(), database() and close()!
*
* Opens the SQLiteDatabase if not already opened.
*
* @return the newly opened database or the existing database.
*/
@Override
public synchronized SQLiteDatabase getWritableDatabase() {
if(database == null){
database = super.getWritableDatabase();
}
openConnections++;
return database;
}
/**
* Open the database. Always pair this call with close() and use database() to get the opened database!
*/
public synchronized void openDatabase(){
getWritableDatabase();
}
/**
* Returns the opened database. Throws an exception if the database has not been opened yet!
* @return the database.
*/
public synchronized SQLiteDatabase database(){
if(database == null){
throw new IllegalStateException("Database has not been opened yet!");
}
return database;
}
@Override
public synchronized void onCreate(SQLiteDatabase db) {
setForeignKeyConstraintsEnabled(db);
for(LocalDatabaseModel model: models){
model.onCreate(db);
}
}
@Override
public synchronized void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
setForeignKeyConstraintsEnabled(db);
for(LocalDatabaseModel model: models){
model.onUpgrade(db, oldVersion, newVersion);
}
}
@Override
public synchronized void onOpen(SQLiteDatabase db) {
setForeignKeyConstraintsEnabled(db);
}
@TargetApi(Build.VERSION_CODES.JELLY_BEAN)
@Override
public synchronized void onConfigure(SQLiteDatabase db) {
db.setForeignKeyConstraintsEnabled(true);
}
private void setForeignKeyConstraintsEnabled(SQLiteDatabase db){
//Skip for Android 4.1 and newer as this is already handled in onConfigure
if(Build.VERSION.SDK_INT < Build.VERSION_CODES.JELLY_BEAN && !db.isReadOnly()) {
db.execSQL("PRAGMA foreign_keys=ON;");
}
}
/* I often have some utility methods in this class too. */
public long getCount(String table){
return DatabaseUtils.queryNumEntries(database(), table);
}
}
Book.java
public final class Book {
private long id = -1;
private String title;
public Book(String title){
this.title = title;
}
private Book(long id, String title){
this.title = title;
this.id = id;
}
public void save(DatabaseController db){
//save or update the book, throw an exception on failure.
}
//More non static methods (getters, setters, database methods) here
public static Book getById(DatabaseController db, long id){
//Do select query and get an existing book from the database.
}
//More static methods here
public static class Model extends LocalDatabaseModel {
public Model(){
}
@Override
public void onUpgrade(SQLiteDatabase database, int oldVersion, int newVersion){
//Implement update logic for this model/table
}
@Override
public void onCreate(SQLiteDatabase database){
//Implement create logic for this model/table
}
}
}
用法
DatabaseController db = DatabaseController.getInstance(context);
db.openDatabase();
Book book = new Book("Alice in Wonderland");
book.save(db);
db.close();