在 Room 数据库中保存多个 Arraylist - 最好的方法是什么？
Saving Multiple Arraylist in Room Database - Best way of doing it?
背景：
我正在尝试为 Cardgame 构建 Deckbuilder。不同的甲板是基于
一个我想在本地保护的数组列表。这意味着你可以创建你的套牌，而不是我希望你能够保护它，然后创建一个新的套牌，能够再次保存它...... -> 这会产生我想要的多个 Arraylists同样安全 class.
问题：
在知道我想要的不仅仅是一个 Arraylist 的情况下，在 Room 中存储 Arraylists 的最佳方式是什么？
据我所知，我必须创建一个实体 class，它基本上会创建一个（？）table，我必须在其中保存数组列表？
有没有更好的方法呢
奖金：
我也喜欢一个基本的例子来说明如何做到这一点，因为这似乎很难靠我自己实现。
非常感谢！
编辑：
代码示例
所以我使用您的代码示例中的基线实现的内容如下：
我创建了 class SaveDeck，它应该能够 保存具有给定 Deckname 的 Deck：
:-
@实体
public class SaveDeck 实现序列化{
@PrimaryKey（自动生成=真）
私人 int _id;
public SaveDeck(int _id, String deckName, int cardImage, int typeImage, Integer cardCost, String cardName, Integer cardNumber) {
this._id = _id;
DeckName = deckName;
CardImage = cardImage;
TypeImage = typeImage;
CardCost = cardCost;
CardName = cardName;
CardNumber = cardNumber;
}
@ColumnInfo(name = "DeckName")
private String DeckName;
@ColumnInfo(name = "CardImage")
private int CardImage;
@ColumnInfo(name = "TypeImage")
private int TypeImage;
@ColumnInfo(name = "CardCost")
private Integer CardCost;
@ColumnInfo(name = "CardName")
private String CardName;
@ColumnInfo(name = "CardNumber")
private Integer CardNumber;
}
我创建了 Dao Class 如下：
:-
@道
public 界面 DeckBuilderDao {
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] insertCards(SaveDeck... saveDecks);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long insertCard(SaveDeck saveDecks);
@Update
public int updateCardBaseEntries(SaveDeck... saveDecks);
@Update
public int updateCardBaseEntry(SaveDeck saveDecks);
@Delete
public int deleteCardBaseEntried(SaveDeck... saveDecks);
@Delete
public int deleteCardBaseEntry(SaveDeck saveDecks);
@Query("SELECT * FROM SaveDeck")
public SaveDeck[] getAllDecks();
//probably I do not need the getAllDecks Query. Right now I only need the following one:
@Query("SELECT * FROM SaveDeck WHERE DeckName = :NameOfDeck ORDER BY DeckName, CardName")
public SaveDeck getOneDeck(String NameOfDeck);
}
进一步创建数据库Class:
@Database(实体={SaveDeck.class}，版本=1)
public 抽象 class SaveDecksDataBase 扩展 RoomDatabase {
public 抽象 DeckBuilderDao deckBuilderDao();
}
终于尝试在我各自的片段中创建设置，这是我挣扎的地方：
:-
public class review_fragment 扩展片段 {
private List<TransferDeck> mTransferDeck = DataHolder.getInstance().savedDecklistTransfer;
SaveDecksDataBase mSavedDecksDB;
Cursor mCursor;
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
//return super.onCreateView(inflater, container, savedInstanceState);
View view = inflater.inflate(R.layout.review_fragment, container, false);
/*Introduce Cards Recycler*/
RecyclerView rvCards = view.findViewById(R.id.rv_review_cardlist);
rvCards.setLayoutManager(new GridLayoutManager(getActivity(), 5));
review_RViewAdapter_Cards adapterCards = new review_RViewAdapter_Cards(getContext(), mTransferDeck);
rvCards.setAdapter(adapterCards);
/*Init Room database*/
mSavedDecksDB = Room.databaseBuilder(getActivity(),SaveDecksDataBase.class,"SavedDecksDB.db").build();
populateDB(mTransferDeck);
return view;
}
private void populateDB(final List<TransferDeck> mTransferDeck) {
new Thread(new Runnable() {
@Override
public void run() {
List<SaveDeck> mSaveDeck = new ArrayList<>();
for(int i = 0; i<mTransferDeck.size(); i++){
mSaveDeck.add(new SaveDeck(i, "FirstSavedDeck", mTransferDeck.get(i).getCardImage() ,mTransferDeck.get(i).getTypeImage(), mTransferDeck.get(i).getCost(), mTransferDeck.get(i).getName(), mTransferDeck.get(i).getNumber()));
}
mSavedDecksDB.deckBuilderDao().insertCards(mSaveDeck);
}
}).start();
}
}
所以现在我不知道如何正确地将新实例添加到我的 Class SaveDeck。我习惯于使用带有构造函数的 Arraylists。 因此我尝试了这种方式。您能否看一下并帮帮我？
What is the best way of storing the Arraylists in Room while knowing
that I want to there is not only one Arraylist coming?
可以说没有办法是最好的办法。
ArrayList 不只是出现，数据和元素结构（如果每个元素存在多个值）来自某个地方，即它们只是容器而不是分组数据的持久容器。由于最终结果似乎是持久的结构化数据集，因此主要利用数据库可能会更简单。
I am trying to build a Deckbuilder for a Cardgame. The different decks
are based on one Arraylists that I want to safe locally.
听起来这是卡牌的基础，即可用于游戏的卡牌。所以听起来你想要 卡片 .
的数据库中的 table
That means you can create your deck and than I want you to be able to
safe it, and then create a new deck,
听起来您想要 套牌 的数据库中有一个 table 并且套牌可以有一张纸牌列表。那么卡数是多少？ 10、20、3000？好吧，如果您利用 Realtional Database Manager 的关系功能（SQLite，因此是 Room（因为后者是 SQLite 之上的抽象层））。因此，很可能被称为映射（引用、关系和同一事物的其他名称）table。
这主要存储关系，该关系由可以标识关系的一部分的列和可以标识另一部分的另一列组成。将此应用于您的情况，DECK 将与多张卡片有关系，一张 CARD 可能会出现在多张 DECK 中。这是映射 table 满足的多对多关系。所以你可能想要一个 mapping table.
为了进一步解释，假设我们正在谈论纸牌（黑桃 A、红心皇后等）。
所以我们需要三个 tables a Card table, a Deck table and a table 将卡片映射到套牌（因此反之亦然） a Card_Deck_Map table.
Card table 为保持简单，cardname 将有一个单独的列。
Deck tables 将有一列用于 deckname
为了提高效率，作为特殊列 rowid 的别名的标识符将用于映射。所以上面的 tables 将每个都有一个额外的列，将被称为 _id（将列命名为 _id 这可能是有益的Android).
假定您不希望重复卡片名称或套牌名称，因此将应用一个 UNIQUE 约束，不允许重复名称。
简而言之，这是 SQL 中的样子（这最终是大多数数据存储、操作和提取的完成方式）：-
-- Delete the tables if they exist (just in case)
DROP TABLE IF EXISTS card_deck_map;
DROP TABLE IF EXISTS card;
DROP TABLE IF EXISTS deck;
-- Create the tables
CREATE TABLE IF NOT EXISTS card (_id INTEGER PRIMARY KEY, cardname UNIQUE);
CREATE TABLE IF NOT EXISTS deck (_id INTEGER PRIMARY KEY, deckname UNIQUE);
CREATE TABLE IF NOT EXISTS card_deck_map (
card_reference INTEGER REFERENCES card(_id),
deck_reference INTEGER REFERENCES deck(_id),
PRIMARY KEY(card_reference,deck_reference)
);
-- Add 3 cards to the card table
INSERT INTO card (cardname) VALUES ('CARD001'),('CARD002'),('CARD003');
-- Add 3 decks to the deck table
INSERT INTO deck (deckname) VALUES ('DECK001'),('DECK002');
-- Create some mapping entries (aka put some cards into each deck)
INSERT INTO card_deck_map VALUES
(1,2), -- _id value for CARD001 should be 1, _id value for DECK002 should be 2
(3,2), -- CARD003 is in DECK002
(2,1), -- CARD002 is in DECK001
(1,1) -- CARD001 is also in DECK002
;
-- Have a look at what we have (ignore the id values they mean little to the user)
SELECT deckname, cardname
FROM deck
JOIN card_deck_map ON deck._id = deck_reference
JOIN card ON card_deck_map.card_reference = card._id
ORDER BY deckname, cardname
;
上面的输出将是：-
所以现在数据库设计看起来很合适，那么它现在可以转换为 ROOM 使用。
首先是 3 个实体 Defining data using Room entities
Card.java
:-
@Entity (indices = {@Index(value = {"cardname"}, unique = true)})
public class Card {
@PrimaryKey(autoGenerate = true)
public long _id;
@ColumnInfo(name = "cardname")
public String cardname;
}
Deck.java
:-
@Entity(indices = {@Index(value = "deckname", unique = true)})
public class Deck {
@PrimaryKey(autoGenerate = true)
public long _id;
@ColumnInfo(name = "deckname")
public String deckname;
}
Card_Deck_Map.java
:-
@Entity(
primaryKeys = {"card_reference","deck_reference"},
foreignKeys = {
@ForeignKey(entity = Card.class,parentColumns = "_id",childColumns = "card_reference"),
@ForeignKey(entity = Deck.class, parentColumns = "_id",childColumns = "deck_reference")}
)
public class Card_Deck_Map {
@ColumnInfo (name="card_reference")
public long card_reference;
@ColumnInfo(name="deck_reference")
public long deck_reference;
}
现在您需要数据访问对象定义Accessing data using Room DAOs
DeckBuildeDao
:-
@道
public 界面 DeckBuilderDao {
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] insertCards(Card... cards);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long insertCard(Card card);
@Update
public int updateCardBaseEntries(Card... cards);
@Update
public int updateCardBaseEntry(Card card);
@Delete
public int deleteCardBaseEntried(Card... cards);
@Delete
public int deleteCardBaseEntry(Card card);
@Query("SELECT * FROM card")
public Card[] getAllCards();
@Query("SELECT * FROM card WHERE _id = :id")
public Card getACard(long id);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] insertDecks(Deck... decks);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long insertDeck(Deck deck);
@Update
public int updateDeckEntries(Deck... decks);
@Update
public int updateDeckEntry(Deck deck);
@Delete
public int deleteDeckEntries(Deck... decks);
@Delete
public int deleteDeckEntry(Deck deck);
@Query("SELECT * FROM deck")
public int getAllDecks();
@Query("SELECT * FROM deck WHERE _id = :id")
public Deck getADeck(long id);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] addCardDeckEntries(Card_Deck_Map... cardDeckMaps);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long addCardDeckEntry(Card_Deck_Map cardDeckMap);
@Query("SELECT Deck._id,Card.cardname, Deck.deckname " +
"FROM deck " +
"JOIN card_deck_map ON deck._id = card_deck_map.deck_reference " +
"JOIN card ON card_deck_map.card_reference = card._id " +
"ORDER BY deckname, cardname")
public Cursor getAllDecksWithCards();
}
A class 用于将实体和 DAO 联系在一起的数据库
DeckBuilderDatabase.java
:-
@Database(entities = {Card.class, Deck.class, Card_Deck_Map.class}, version = 1)
public abstract class DeckBuilderDatabase extends RoomDatabase {
public abstract DeckBuilderDao deckBuilderDao();
}
现在 activity 使用数据库。
在这个工作示例中；
数据库将填充 2 副牌（Deck001 和 Deck002），根据一副扑克牌减去 Jokers 的卡片基础。
- 纸牌的名称将类似于黑桃 A、红心 2。
牌组将加载一些卡片（映射）
- Deck002 包含所有 52 张牌。
- Deck001 有 3 张牌。
Decks 和 Cards 将从数据库中提取并用于填充 ListView。
MainActivity.java
public class MainActivity extends AppCompatActivity {
public static final String[] SUITS = new String[]{"Spades","Hearts","Clubs","Diamons"};
public static final int CARDS_IN_A_SUIT = 13;
DeckBuilderDatabase mDBDB;
SimpleCursorAdapter mSCA;
ListView mDecks_and_Cards_List;
Cursor mCursor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDecks_and_Cards_List = this.findViewById(R.id.decksandcards);
mDBDB = Room.databaseBuilder(this,DeckBuilderDatabase.class,"deckbuilder.db").build();
populateDB();
}
/**
* Populate the DB with some data, extract the data in the DB and setup the ListView
*/
private void populateDB() {
new Thread(new Runnable() {
@Override
public void run() {
Card_Deck_Map currentcdm = new Card_Deck_Map();
Deck[] decks_to_add = new Deck[]{new Deck(), new Deck()};
decks_to_add[0].deckname = "DECK001";
decks_to_add[1].deckname= "DECK002";
mDBDB.deckBuilderDao().insertDecks(decks_to_add);
// Build Card base pack of 52 (no Jokers)
Card[] cardstoadd = new Card[CARDS_IN_A_SUIT * SUITS.length];
int counter = 0;
for (int suit = 0; suit < SUITS.length; suit++) {
for (int cardval = 0; cardval < CARDS_IN_A_SUIT; cardval++) {
Card thiscard = new Card();
String thiscardname = generateCardValueDescription(cardval+1,suit);
thiscard.cardname = thiscardname;
cardstoadd[counter++] = thiscard;
}
}
mDBDB.deckBuilderDao().insertCards(cardstoadd);
// Populate the decks with cards Deck002 has full pack of 52 Deck001 has 3 cards
Card_Deck_Map[] mappings = new Card_Deck_Map[55];
for (int cardid = 1; cardid < 53; cardid++) {
Card_Deck_Map cdm = new Card_Deck_Map();
cdm.deck_reference = 2;
cdm.card_reference = cardid;
mappings[cardid-1] = cdm;
}
Card_Deck_Map cdm53 = new Card_Deck_Map();
cdm53.card_reference = 19;
cdm53.deck_reference = 1;
mappings[52] = cdm53;
Card_Deck_Map cdm54 = new Card_Deck_Map();
cdm54.card_reference = 10;
cdm54.deck_reference = 1;
mappings[53] = cdm54;
Card_Deck_Map cdm55 = new Card_Deck_Map();
cdm55.card_reference = 23;
cdm55.deck_reference = 1;
mappings[54] = cdm55;
mDBDB.deckBuilderDao().addCardDeckEntries(mappings);
// Get the Decks and cards in the decks
mCursor = mDBDB.deckBuilderDao().getAllDecksWithCards();
setupOrRefeshListView();
}
}).start();
}
/**
* Handles the ListView (also write data to the log for debugging)
*/
private void setupOrRefeshListView() {
int rowcount = mCursor.getCount();
Log.d("ROWS","Number of rows in the Cursor is " + String.valueOf(rowcount));
while (mCursor.moveToNext()) {
Log.d(
"ROWS",
"Row " +
String.valueOf(mCursor.getPosition()) +
" Has a deck called " +
mCursor.getString(mCursor.getColumnIndex("deckname")) +
" and a card called " +
mCursor.getString(mCursor.getColumnIndex("cardname"))
);
}
if (mSCA == null) {
mSCA = new SimpleCursorAdapter(
this,
android.R.layout.simple_list_item_2,
mCursor,
new String[]{
"deckname",
"cardname"},
new int[]{
android.R.id.text1,
android.R.id.text2},
0
);
mDecks_and_Cards_List.setAdapter(mSCA);
} else {
mSCA.swapCursor(mCursor);
}
}
/**
* Converts numeric cardvalue (1-13) and suit to a decriptive name
* @param cardvalue
* @param suit
* @return
*/
private String generateCardValueDescription(int cardvalue, int suit) {
String rv;
switch (cardvalue) {
case 1:
rv = "Ace of " + SUITS[suit];
break;
case 11:
rv = "Jack of " + SUITS[suit];
break;
case 12:
rv = "Queen of " + SUITS[suit];
break;
case 13:
rv = "King of " + SUITS[suit];
break;
default:
rv = String.valueOf(cardvalue) + " of " + SUITS[suit];
}
return rv;
}
}
生成的迷你应用程序：-
背景： 我正在尝试为 Cardgame 构建 Deckbuilder。不同的甲板是基于 一个我想在本地保护的数组列表。这意味着你可以创建你的套牌，而不是我希望你能够保护它，然后创建一个新的套牌，能够再次保存它...... -> 这会产生我想要的多个 Arraylists同样安全 class.
问题： 在知道我想要的不仅仅是一个 Arraylist 的情况下，在 Room 中存储 Arraylists 的最佳方式是什么？
据我所知，我必须创建一个实体 class，它基本上会创建一个（？）table，我必须在其中保存数组列表？
有没有更好的方法呢
奖金： 我也喜欢一个基本的例子来说明如何做到这一点，因为这似乎很难靠我自己实现。
非常感谢！
编辑：
代码示例
所以我使用您的代码示例中的基线实现的内容如下：
我创建了 class SaveDeck，它应该能够 保存具有给定 Deckname 的 Deck： :-
@实体 public class SaveDeck 实现序列化{ @PrimaryKey（自动生成=真） 私人 int _id;
public SaveDeck(int _id, String deckName, int cardImage, int typeImage, Integer cardCost, String cardName, Integer cardNumber) { this._id = _id; DeckName = deckName; CardImage = cardImage; TypeImage = typeImage; CardCost = cardCost; CardName = cardName; CardNumber = cardNumber; } @ColumnInfo(name = "DeckName") private String DeckName; @ColumnInfo(name = "CardImage") private int CardImage; @ColumnInfo(name = "TypeImage") private int TypeImage; @ColumnInfo(name = "CardCost") private Integer CardCost; @ColumnInfo(name = "CardName") private String CardName; @ColumnInfo(name = "CardNumber") private Integer CardNumber;}
我创建了 Dao Class 如下： :-
@道 public 界面 DeckBuilderDao {
@Insert(onConflict = OnConflictStrategy.IGNORE) public long[] insertCards(SaveDeck... saveDecks); @Insert(onConflict = OnConflictStrategy.IGNORE) public long insertCard(SaveDeck saveDecks); @Update public int updateCardBaseEntries(SaveDeck... saveDecks); @Update public int updateCardBaseEntry(SaveDeck saveDecks); @Delete public int deleteCardBaseEntried(SaveDeck... saveDecks); @Delete public int deleteCardBaseEntry(SaveDeck saveDecks); @Query("SELECT * FROM SaveDeck") public SaveDeck[] getAllDecks(); //probably I do not need the getAllDecks Query. Right now I only need the following one: @Query("SELECT * FROM SaveDeck WHERE DeckName = :NameOfDeck ORDER BY DeckName, CardName") public SaveDeck getOneDeck(String NameOfDeck);}
进一步创建数据库Class:
@Database(实体={SaveDeck.class}，版本=1) public 抽象 class SaveDecksDataBase 扩展 RoomDatabase { public 抽象 DeckBuilderDao deckBuilderDao(); }
终于尝试在我各自的片段中创建设置，这是我挣扎的地方： :-
public class review_fragment 扩展片段 {
private List<TransferDeck> mTransferDeck = DataHolder.getInstance().savedDecklistTransfer; SaveDecksDataBase mSavedDecksDB; Cursor mCursor; public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) { //return super.onCreateView(inflater, container, savedInstanceState); View view = inflater.inflate(R.layout.review_fragment, container, false); /*Introduce Cards Recycler*/ RecyclerView rvCards = view.findViewById(R.id.rv_review_cardlist); rvCards.setLayoutManager(new GridLayoutManager(getActivity(), 5)); review_RViewAdapter_Cards adapterCards = new review_RViewAdapter_Cards(getContext(), mTransferDeck); rvCards.setAdapter(adapterCards); /*Init Room database*/ mSavedDecksDB = Room.databaseBuilder(getActivity(),SaveDecksDataBase.class,"SavedDecksDB.db").build(); populateDB(mTransferDeck); return view; } private void populateDB(final List<TransferDeck> mTransferDeck) { new Thread(new Runnable() { @Override public void run() { List<SaveDeck> mSaveDeck = new ArrayList<>(); for(int i = 0; i<mTransferDeck.size(); i++){ mSaveDeck.add(new SaveDeck(i, "FirstSavedDeck", mTransferDeck.get(i).getCardImage() ,mTransferDeck.get(i).getTypeImage(), mTransferDeck.get(i).getCost(), mTransferDeck.get(i).getName(), mTransferDeck.get(i).getNumber())); } mSavedDecksDB.deckBuilderDao().insertCards(mSaveDeck); } }).start(); }}
所以现在我不知道如何正确地将新实例添加到我的 Class SaveDeck。我习惯于使用带有构造函数的 Arraylists。 因此我尝试了这种方式。您能否看一下并帮帮我？
What is the best way of storing the Arraylists in Room while knowing that I want to there is not only one Arraylist coming?
可以说没有办法是最好的办法。
ArrayList 不只是出现，数据和元素结构（如果每个元素存在多个值）来自某个地方，即它们只是容器而不是分组数据的持久容器。由于最终结果似乎是持久的结构化数据集，因此主要利用数据库可能会更简单。
I am trying to build a Deckbuilder for a Cardgame. The different decks are based on one Arraylists that I want to safe locally.
听起来这是卡牌的基础，即可用于游戏的卡牌。所以听起来你想要 卡片 .
的数据库中的 tableThat means you can create your deck and than I want you to be able to safe it, and then create a new deck,
听起来您想要 套牌 的数据库中有一个 table 并且套牌可以有一张纸牌列表。那么卡数是多少？ 10、20、3000？好吧，如果您利用 Realtional Database Manager 的关系功能（SQLite，因此是 Room（因为后者是 SQLite 之上的抽象层））。因此，很可能被称为映射（引用、关系和同一事物的其他名称）table。
这主要存储关系，该关系由可以标识关系的一部分的列和可以标识另一部分的另一列组成。将此应用于您的情况，DECK 将与多张卡片有关系，一张 CARD 可能会出现在多张 DECK 中。这是映射 table 满足的多对多关系。所以你可能想要一个 mapping table.
为了进一步解释，假设我们正在谈论纸牌（黑桃 A、红心皇后等）。
所以我们需要三个 tables a Card table, a Deck table and a table 将卡片映射到套牌（因此反之亦然） a Card_Deck_Map table.
Card table 为保持简单，cardname 将有一个单独的列。 Deck tables 将有一列用于 deckname 为了提高效率，作为特殊列 rowid 的别名的标识符将用于映射。所以上面的 tables 将每个都有一个额外的列，将被称为 _id（将列命名为 _id 这可能是有益的Android).
假定您不希望重复卡片名称或套牌名称，因此将应用一个 UNIQUE 约束，不允许重复名称。
简而言之，这是 SQL 中的样子（这最终是大多数数据存储、操作和提取的完成方式）：-
-- Delete the tables if they exist (just in case)
DROP TABLE IF EXISTS card_deck_map;
DROP TABLE IF EXISTS card;
DROP TABLE IF EXISTS deck;
-- Create the tables
CREATE TABLE IF NOT EXISTS card (_id INTEGER PRIMARY KEY, cardname UNIQUE);
CREATE TABLE IF NOT EXISTS deck (_id INTEGER PRIMARY KEY, deckname UNIQUE);
CREATE TABLE IF NOT EXISTS card_deck_map (
card_reference INTEGER REFERENCES card(_id),
deck_reference INTEGER REFERENCES deck(_id),
PRIMARY KEY(card_reference,deck_reference)
);
-- Add 3 cards to the card table
INSERT INTO card (cardname) VALUES ('CARD001'),('CARD002'),('CARD003');
-- Add 3 decks to the deck table
INSERT INTO deck (deckname) VALUES ('DECK001'),('DECK002');
-- Create some mapping entries (aka put some cards into each deck)
INSERT INTO card_deck_map VALUES
(1,2), -- _id value for CARD001 should be 1, _id value for DECK002 should be 2
(3,2), -- CARD003 is in DECK002
(2,1), -- CARD002 is in DECK001
(1,1) -- CARD001 is also in DECK002
;
-- Have a look at what we have (ignore the id values they mean little to the user)
SELECT deckname, cardname
FROM deck
JOIN card_deck_map ON deck._id = deck_reference
JOIN card ON card_deck_map.card_reference = card._id
ORDER BY deckname, cardname
;
上面的输出将是：-
所以现在数据库设计看起来很合适，那么它现在可以转换为 ROOM 使用。
首先是 3 个实体 Defining data using Room entities
Card.java
:-
@Entity (indices = {@Index(value = {"cardname"}, unique = true)})
public class Card {
@PrimaryKey(autoGenerate = true)
public long _id;
@ColumnInfo(name = "cardname")
public String cardname;
}
Deck.java
:-
@Entity(indices = {@Index(value = "deckname", unique = true)})
public class Deck {
@PrimaryKey(autoGenerate = true)
public long _id;
@ColumnInfo(name = "deckname")
public String deckname;
}
Card_Deck_Map.java
:-
@Entity(
primaryKeys = {"card_reference","deck_reference"},
foreignKeys = {
@ForeignKey(entity = Card.class,parentColumns = "_id",childColumns = "card_reference"),
@ForeignKey(entity = Deck.class, parentColumns = "_id",childColumns = "deck_reference")}
)
public class Card_Deck_Map {
@ColumnInfo (name="card_reference")
public long card_reference;
@ColumnInfo(name="deck_reference")
public long deck_reference;
}
现在您需要数据访问对象定义Accessing data using Room DAOs
DeckBuildeDao
:-
@道 public 界面 DeckBuilderDao {
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] insertCards(Card... cards);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long insertCard(Card card);
@Update
public int updateCardBaseEntries(Card... cards);
@Update
public int updateCardBaseEntry(Card card);
@Delete
public int deleteCardBaseEntried(Card... cards);
@Delete
public int deleteCardBaseEntry(Card card);
@Query("SELECT * FROM card")
public Card[] getAllCards();
@Query("SELECT * FROM card WHERE _id = :id")
public Card getACard(long id);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] insertDecks(Deck... decks);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long insertDeck(Deck deck);
@Update
public int updateDeckEntries(Deck... decks);
@Update
public int updateDeckEntry(Deck deck);
@Delete
public int deleteDeckEntries(Deck... decks);
@Delete
public int deleteDeckEntry(Deck deck);
@Query("SELECT * FROM deck")
public int getAllDecks();
@Query("SELECT * FROM deck WHERE _id = :id")
public Deck getADeck(long id);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long[] addCardDeckEntries(Card_Deck_Map... cardDeckMaps);
@Insert(onConflict = OnConflictStrategy.IGNORE)
public long addCardDeckEntry(Card_Deck_Map cardDeckMap);
@Query("SELECT Deck._id,Card.cardname, Deck.deckname " +
"FROM deck " +
"JOIN card_deck_map ON deck._id = card_deck_map.deck_reference " +
"JOIN card ON card_deck_map.card_reference = card._id " +
"ORDER BY deckname, cardname")
public Cursor getAllDecksWithCards();
}
A class 用于将实体和 DAO 联系在一起的数据库
DeckBuilderDatabase.java
:-
@Database(entities = {Card.class, Deck.class, Card_Deck_Map.class}, version = 1)
public abstract class DeckBuilderDatabase extends RoomDatabase {
public abstract DeckBuilderDao deckBuilderDao();
}
现在 activity 使用数据库。
在这个工作示例中；
数据库将填充 2 副牌（Deck001 和 Deck002），根据一副扑克牌减去 Jokers 的卡片基础。
- 纸牌的名称将类似于黑桃 A、红心 2。
牌组将加载一些卡片（映射）
- Deck002 包含所有 52 张牌。
- Deck001 有 3 张牌。
Decks 和 Cards 将从数据库中提取并用于填充 ListView。
MainActivity.java
public class MainActivity extends AppCompatActivity {
public static final String[] SUITS = new String[]{"Spades","Hearts","Clubs","Diamons"};
public static final int CARDS_IN_A_SUIT = 13;
DeckBuilderDatabase mDBDB;
SimpleCursorAdapter mSCA;
ListView mDecks_and_Cards_List;
Cursor mCursor;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDecks_and_Cards_List = this.findViewById(R.id.decksandcards);
mDBDB = Room.databaseBuilder(this,DeckBuilderDatabase.class,"deckbuilder.db").build();
populateDB();
}
/**
* Populate the DB with some data, extract the data in the DB and setup the ListView
*/
private void populateDB() {
new Thread(new Runnable() {
@Override
public void run() {
Card_Deck_Map currentcdm = new Card_Deck_Map();
Deck[] decks_to_add = new Deck[]{new Deck(), new Deck()};
decks_to_add[0].deckname = "DECK001";
decks_to_add[1].deckname= "DECK002";
mDBDB.deckBuilderDao().insertDecks(decks_to_add);
// Build Card base pack of 52 (no Jokers)
Card[] cardstoadd = new Card[CARDS_IN_A_SUIT * SUITS.length];
int counter = 0;
for (int suit = 0; suit < SUITS.length; suit++) {
for (int cardval = 0; cardval < CARDS_IN_A_SUIT; cardval++) {
Card thiscard = new Card();
String thiscardname = generateCardValueDescription(cardval+1,suit);
thiscard.cardname = thiscardname;
cardstoadd[counter++] = thiscard;
}
}
mDBDB.deckBuilderDao().insertCards(cardstoadd);
// Populate the decks with cards Deck002 has full pack of 52 Deck001 has 3 cards
Card_Deck_Map[] mappings = new Card_Deck_Map[55];
for (int cardid = 1; cardid < 53; cardid++) {
Card_Deck_Map cdm = new Card_Deck_Map();
cdm.deck_reference = 2;
cdm.card_reference = cardid;
mappings[cardid-1] = cdm;
}
Card_Deck_Map cdm53 = new Card_Deck_Map();
cdm53.card_reference = 19;
cdm53.deck_reference = 1;
mappings[52] = cdm53;
Card_Deck_Map cdm54 = new Card_Deck_Map();
cdm54.card_reference = 10;
cdm54.deck_reference = 1;
mappings[53] = cdm54;
Card_Deck_Map cdm55 = new Card_Deck_Map();
cdm55.card_reference = 23;
cdm55.deck_reference = 1;
mappings[54] = cdm55;
mDBDB.deckBuilderDao().addCardDeckEntries(mappings);
// Get the Decks and cards in the decks
mCursor = mDBDB.deckBuilderDao().getAllDecksWithCards();
setupOrRefeshListView();
}
}).start();
}
/**
* Handles the ListView (also write data to the log for debugging)
*/
private void setupOrRefeshListView() {
int rowcount = mCursor.getCount();
Log.d("ROWS","Number of rows in the Cursor is " + String.valueOf(rowcount));
while (mCursor.moveToNext()) {
Log.d(
"ROWS",
"Row " +
String.valueOf(mCursor.getPosition()) +
" Has a deck called " +
mCursor.getString(mCursor.getColumnIndex("deckname")) +
" and a card called " +
mCursor.getString(mCursor.getColumnIndex("cardname"))
);
}
if (mSCA == null) {
mSCA = new SimpleCursorAdapter(
this,
android.R.layout.simple_list_item_2,
mCursor,
new String[]{
"deckname",
"cardname"},
new int[]{
android.R.id.text1,
android.R.id.text2},
0
);
mDecks_and_Cards_List.setAdapter(mSCA);
} else {
mSCA.swapCursor(mCursor);
}
}
/**
* Converts numeric cardvalue (1-13) and suit to a decriptive name
* @param cardvalue
* @param suit
* @return
*/
private String generateCardValueDescription(int cardvalue, int suit) {
String rv;
switch (cardvalue) {
case 1:
rv = "Ace of " + SUITS[suit];
break;
case 11:
rv = "Jack of " + SUITS[suit];
break;
case 12:
rv = "Queen of " + SUITS[suit];
break;
case 13:
rv = "King of " + SUITS[suit];
break;
default:
rv = String.valueOf(cardvalue) + " of " + SUITS[suit];
}
return rv;
}
}