如何定义多个实体？

Question

static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(SupportSQLiteDatabase database) {
            database.execSQL("CREATE TABLE IF NOT EXISTS `invoice` (`invoice_id` VARCHAR, "
                    + "`terminal_no` VARCHAR NOT NULL, `cashier_name` TEXT,  PRIMARY KEY(`invoice_id`))");
        }
    };

Room.databaseBuilder(context.getApplicationContext(),
                                    POSDatabase.class,
                                 "pos_database").addMigrations(MIGRATION_1_2).build();

package com.example.qrreceipt;

import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "item")
public class Item {
    @PrimaryKey
    @NonNull
    @ColumnInfo(name = "item_id")
    private String item_id;

    @ColumnInfo(name = "description")
    private String description;

    @ColumnInfo(name = "price")
    private double price;

    public Item() { }

    @NonNull
    public String getItem_id() {
        return item_id;
    }

    public String getDescription() {
        return description;
    }

    public double getPrice() {
        return price;
    }

    public void setItem_id(@NonNull String item_id) {
        this.item_id = item_id;
    }

    public void setDescription(String description) {
        this.description = description;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

itemdao.java

package com.example.qrreceipt;

import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface ItemDao {
    @Insert
    void insertItem(Item item);

    @Update
    void updateItem(Item item);

    @Query("SELECT * FROM item WHERE item_id = :item_id")
    List<Item> findItem(String item_id);

    @Query("SELECT * FROM item")
    List<Item> getAllItems();

    @Query("DELETE FROM item WHERE item_id = :item_id")
    void deleteItem(String item_id);
}

posDatabase.java

package com.example.qrreceipt;

import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import androidx.room.migration.Migration;
import androidx.sqlite.db.SupportSQLiteDatabase;

@Database(entities = {Item.class, Invoice.class}, version = 2, exportSchema = false)
public abstract class POSDatabase extends RoomDatabase {
    public abstract ItemDao getItemDAO();
    public abstract InvoiceDao getInvoiceDAO();

    private static POSDatabase INSTANCE;

    static final Migration MIGRATION_1_2 = new Migration(1, 2) {
        @Override
        public void migrate(SupportSQLiteDatabase database) {
            database.execSQL("CREATE TABLE IF NOT EXISTS `invoice` (`invoice_id` VARCHAR, "
                    + "`terminal_no` VARCHAR NOT NULL, `cashier_name` TEXT,  PRIMARY KEY(`invoice_id`))");
        }
    };

    static POSDatabase getDatabase(final Context context) {
        if (INSTANCE == null) {
            synchronized (POSDatabase.class) {
                if (INSTANCE == null) {
                    INSTANCE =
                            Room.databaseBuilder(context.getApplicationContext(),
                                    POSDatabase.class,
                                 "pos_database").addMigrations(MIGRATION_1_2).build();

                }
            }
        }
        return INSTANCE;
    }
}

invoice.java

package com.example.qrreceipt;

import androidx.annotation.NonNull;
import androidx.room.ColumnInfo;
import androidx.room.Entity;
import androidx.room.PrimaryKey;

@Entity(tableName = "invoice")
public class Invoice {
    @PrimaryKey
    @NonNull
    @ColumnInfo(name = "invoice_id")
    private String invoice_id;

    //private Date date;

    @ColumnInfo(name = "terminal_no")
    private String terminal_no;

    @ColumnInfo(name = "cashier_name")
    private String cashier_name;

    public Invoice() { }

    @NonNull
    public String getInvoice_id() {
        return invoice_id;
    }

    public String getTerminal_no() {
        return terminal_no;
    }

    public String getCashier_name() {
        return cashier_name;
    }

    public void setInvoice_id(@NonNull String invoice_id) {
        this.invoice_id = invoice_id;
    }

    public void setTerminal_no(String terminal_no) {
        this.terminal_no = terminal_no;
    }

    public void setCashier_name(String cashier_name) {
        this.cashier_name = cashier_name;
    }
}

package com.example.qrreceipt;

import androidx.room.Dao;
import androidx.room.Insert;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface InvoiceDao {
    @Insert
    void insertInvoice(Invoice invoice);

    @Update
    void updateInvoice(Invoice invoice);

    @Query("SELECT * FROM invoice WHERE invoice_id = :invoice_id")
    List<Item> findInvoice(String invoice_id);

    @Query("SELECT * FROM invoice")
    List<Item> getAllInvoices();

    @Query("DELETE FROM invoice WHERE invoice_id = :invoice_id")
    void deleteInvoice(String invoice_id);
}

错误：错误：查询返回的列在com.example.qrreceipt.Item中没有字段[item_id,price]，即使它们被注释为非空或原语。查询返回的列:[invoice_id,terminal_no,cashier_name]

Answer 1

您当前的问题是，您正试图从发票表中获取项目。

这就是下面所说的：-

错误：查询返回的列在com.example.qrreceipt.Item中没有字段[item_id,price]，即使它们被注释为非空或原语。查询返回的列:[invoice_id,terminal_no,cashier_name]

@Query("SELECT * FROM invoice WHERE invoice_id = :invoice_id")
List<Invoice> findInvoice(String invoice_id);


@Query("SELECT * FROM invoice")
List<Invoice> getAllInvoices();

null

使用：-

database.execSQL("CREATE TABLE IF NOT EXISTS `invoice` (`invoice_id` TEXT NOT NULL, "
                + "`terminal_no` TEXT NOT NULL, `cashier_name` TEXT,  PRIMARY KEY(`invoice_id`))");

连同：-

@Entity(tableName = "invoice")
public class Invoice {
    @PrimaryKey
    @NonNull
    @ColumnInfo(name = "invoice_id")
    private String invoice_id;

    //private Date date;

    @NonNull
    @ColumnInfo(name = "terminal_no")
    private String terminal_no;

    @ColumnInfo(name = "cashier_name")
    private String cashier_name;

    public Invoice() { }

    @NonNull
    public String getInvoice_id() {
        return invoice_id;
    }

    public String getTerminal_no() {
        return terminal_no;
    }

    public String getCashier_name() {
        return cashier_name;
    }

    public void setInvoice_id(@NonNull String invoice_id) {
        this.invoice_id = invoice_id;
    }

    public void setTerminal_no(String terminal_no) {
        this.terminal_no = terminal_no;
    }

    public void setCashier_name(String cashier_name) {
        this.cashier_name = cashier_name;
    }
}

应该管用。