房间：如何 link 对象 ID 到成员 ID

Question

我使用 Android 房间数据库。

我有一个实体 "Member" 和一个实体 "Transaction"。我想创建一个新的交易（例如买一本书）。然后我想 link 所有成员（每个 id）和交易 id。这意味着如果有 5 个人购买了这本书，那么我想要 link 5 个带有交易 ID 的 ID。

在我这样做之后，会员中的余额应该发生变化（例如，会员有 20 欧元，而这本书的成本为 10，交易后 - 会员应该有 10 欧元）。

我有 activity 创建新交易的权限。现在我想创建一个新的 activity，它应该在 NewTransactionActivity 之后启动，以处理成员对交易的 linking。

我如何 link 具有多个会员 ID 的交易 ID？另外，如何使用 BigDecimal 进行计算？所以当我进行新交易时，每个 linked 成员的余额都应该改变。

现在，我的余额是 double 类型，但我要更改它。

Class 交易：

@Entity(tableName = "transaction_table")
public class Transaction {

@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = "TransactionID")
private long id;

@ColumnInfo(name = "Transaction Name")
private String transactionName;

@ColumnInfo(name = "Transaction Balance")
private double balance;

public double getBalance() {
    return balance;
}

public void setBalance(double balance) {
    this.balance = balance;
}

public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public String getTransactionName() {
    return transactionName;
}

public void setTransactionName(String transactionName) {
    this.transactionName = transactionName;
}

public Transaction(String transactionName, double balance) {
    this.transactionName = transactionName;
    this.balance = balance;
}

}

Class 会员:

@Entity(tableName = "member_table")
public class Member {


@PrimaryKey(autoGenerate = true)
@ColumnInfo(name = "MemberID")
private long id;

@ColumnInfo(name = "First Name")
private String firstname;

@ColumnInfo(name = "Surname")
private String surname;

@ColumnInfo(name = "Balance")
private double balance;

public String getFirstname() {
    return firstname;
}

public void setFirstname(String firstname) {
    this.firstname = firstname;
}

public String getSurname() {
    return surname;
}

public void setSurname(String surname) {
    this.surname = surname;
}

public double getBalance() {
    return balance;
}

public void setBalance(double balance) {
    this.balance = balance;
}

public long getId() {
    return id;
}

public void setId(long id) {
    this.id = id;
}

public Member(String firstname, String surname) {
    this.firstname = firstname;
    this.surname = surname;
    this.balance = 0;
}

}

新交易Activity：

public class NewTransactionActivity extends AppCompatActivity {

public static final String EXTRA_REPLY = "com.example.android.transactionlistsql.REPLY";
public static final String EXTRA_REPLY2 = "com.example.android.transactionlistsql.REPLY2";

private EditText mEditTextTransaction;
private EditText mEditTextTransaction2;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.newtransaction_activity);
    mEditTextTransaction = findViewById(R.id.NewTransactionName);
    mEditTextTransaction2 = findViewById(R.id.NewTransactionBalance);
    mEditTextTransaction2.setInputType(InputType.TYPE_CLASS_NUMBER | InputType.TYPE_NUMBER_FLAG_DECIMAL);
    mEditTextTransaction2.setText("0");
    final Button button = findViewById(R.id.NewTransactionButtonSave);

    button.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            Intent replyIntent = new Intent();
            if (TextUtils.isEmpty(mEditTextTransaction.getText())){
                Toast.makeText(getApplicationContext(), R.string.TransactionNameMissing, Toast.LENGTH_LONG).show();
                return;
                //setResult(RESULT_CANCELED, replyIntent);
            }
            else if (TextUtils.isEmpty(mEditTextTransaction2.getText())){
                mEditTextTransaction2.setText("0");
            }
            else {                   
                String newtransactionname = mEditTextTransaction.getText().toString()
                double newtransactionbalance = Double.parseDouble(mEditTextTransaction2.getText().toString()));
                replyIntent.putExtra(EXTRA_REPLY, newtransactionname);
                replyIntent.putExtra(EXTRA_REPLY2, newtransactionbalance);
                setResult(RESULT_OK, replyIntent);
            }
            finish();
        }
    });
}
}

Answer 1

在您的 Transaction.java 实体 class 中添加 MemberId，同时将 @ForeignKey 设置为 Member.java 实体 class。

Transaction.java

import static android.arch.persistence.room.ForeignKey.CASCADE;

@Entity(tableName = "transaction_table", foreignKeys = @ForeignKey(entity = Member.class,
        parentColumns = "MemberID",
        childColumns = "member_id",
        onDelete = CASCADE))
public class Transaction {


    @PrimaryKey(autoGenerate = true)
    @ColumnInfo(name = "TransactionID")
    private long id;

    @ColumnInfo(name = "member_id")
    private long MemberId;

    public long getMemberId() {
    return MemberId;
    }

    public void setMemberId(long memberId) {
        MemberId = memberId;
    }

    //Rest of the fields
}

How do I link a transaction id with multiple member ids?

如果您的应用程序中存在拆分付款，那么您必须将交易 ID 映射到多个成员。

以上代码将映射 Member 和 Transaction 之间的一对多关系 table。一个会员可以做很多笔交易。

您可以通过以下查询获取所有用户的交易：

@Query("SELECT * FROM transaction_table tt INNER JOIN member_table mt on tt.member_id = mt.MemberID WHERE member_id =:memberId")
List<Transaction> getMemberTransactions(long memberId);

要更新会员的余额，您必须编写更新余额查询，其中您必须检查会员的可用余额，并且必须从会员的总余额中扣除交易金额，这将反映在 [=31 的余额列=].

房间：如何 link 对象 ID 到成员 ID

Room: How to link an object id to a member id

android

android-room