我目前正在为销售点 Activity 构建库存管理应用程序。在这里，我需要包含一个包含 3 个表的数据库功能:项目、发票和购物车。根据官方 Android 文档 (https://developer.android.com/training/data-storage/sqlite)，强烈建议使用 Room 库，因为没有它的缺点:没有编译时验证，大量样板代码。有了这个，我决定试一试。
首先，我开始使用一张表来测试 Room 的实现。为了定义 item，我创建了 3 个对象:Item 类、ItemDao 接口(interface)和 POSDatabase 类。结果，所有查询都成功运行。
但是，当我尝试引入另一个实体发票时，它会在生成期间在运行构建和 Java 编译器上产生错误。我尝试按照 Suslov (https://medium.com/@kirillsuslov/how-to-add-more-that-one-entity-in-room-5cc3743219c0) 的建议迁移数据库来解决此问题。尽管进行了编辑，但仍会产生类似的错误。
最后，我想知道使用 Room 定义多个表的正确方法是什么。但是，除此之外，我还需要一些关于错误的启示。感谢您的关注。
尝试的解决方法
根据 Suslov 的说法，需要进行迁移才能将其他表引入数据库。消息来源还提到，迁移的定义要放在 RoomDatabase 继承者(POSDatabase)中。
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`))");
}
};
然后在调用过程中包含 MIGRATION_1_2:
Room.databaseBuilder(context.getApplicationContext(),
POSDatabase.class,
"pos_database").addMigrations(MIGRATION_1_2).build();
项目.java
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;
}
}
发票.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;
}
}
发票道.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 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);
}
运行构建 > 运行任务 > :app:compileDebugJavaWithJavac
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':app:compileDebugJavaWithJavac'. at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:95) at org.gradle.api.internal.tasks.execution.ResolveTaskOutputCachingStateExecuter.execute(ResolveTaskOutputCachingStateExecuter.java:91) at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:57) at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:119) at org.gradle.api.internal.tasks.execution.ResolvePreviousStateExecuter.execute(ResolvePreviousStateExecuter.java:43) at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:93) at org.gradle.api.internal.tasks.execution.FinalizePropertiesTaskExecuter.execute(FinalizePropertiesTaskExecuter.java:45) at org.gradle.api.internal.tasks.execution.ResolveTaskArtifactStateTaskExecuter.execute(ResolveTaskArtifactStateTaskExecuter.java:94) at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:56) at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:55) at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:36) at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.executeTask(EventFiringTaskExecuter.java:67) at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:52) at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.call(EventFiringTaskExecuter.java:49) at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:315) at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:305) at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:175) at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:101) at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36) at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:49) at org.gradle.execution.plan.LocalTaskNodeExecutor.execute(LocalTaskNodeExecutor.java:43) at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:355) at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$InvokeNodeExecutorsAction.execute(DefaultTaskExecutionGraph.java:343) at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:336) at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$BuildOperationAwareExecutionAction.execute(DefaultTaskExecutionGraph.java:322) at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:134) at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker$1.execute(DefaultPlanExecutor.java:129) at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.execute(DefaultPlanExecutor.java:202) at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.executeNextNode(DefaultPlanExecutor.java:193) at org.gradle.execution.plan.DefaultPlanExecutor$ExecutorWorker.run(DefaultPlanExecutor.java:129) at org.gradle.internal.concurrent.ExecutorPolicy$CatchAndRecordFailures.onExecute(ExecutorPolicy.java:63) at org.gradle.internal.concurrent.ManagedExecutorImpl$1.run(ManagedExecutorImpl.java:46) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55) at java.lang.Thread.run(Thread.java:745) Caused by: org.gradle.api.internal.tasks.compile.CompilationFailedException: Compilation failed; see the compiler error output for details. at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:52) at org.gradle.api.internal.tasks.compile.JdkJavaCompiler.execute(JdkJavaCompiler.java:36) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.delegateAndHandleErrors(NormalizingJavaCompiler.java:100) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:52) at org.gradle.api.internal.tasks.compile.NormalizingJavaCompiler.execute(NormalizingJavaCompiler.java:38) at org.gradle.api.internal.tasks.compile.AnnotationProcessorDiscoveringCompiler.execute(AnnotationProcessorDiscoveringCompiler.java:51) at org.gradle.api.internal.tasks.compile.AnnotationProcessorDiscoveringCompiler.execute(AnnotationProcessorDiscoveringCompiler.java:37) at org.gradle.api.internal.tasks.compile.CleaningJavaCompilerSupport.execute(CleaningJavaCompilerSupport.java:39) at org.gradle.api.internal.tasks.compile.incremental.IncrementalCompilerFactory$2.execute(IncrementalCompilerFactory.java:110) at org.gradle.api.internal.tasks.compile.incremental.IncrementalCompilerFactory$2.execute(IncrementalCompilerFactory.java:106) at org.gradle.api.internal.tasks.compile.incremental.IncrementalResultStoringCompiler.execute(IncrementalResultStoringCompiler.java:59) at org.gradle.api.internal.tasks.compile.incremental.IncrementalResultStoringCompiler.execute(IncrementalResultStoringCompiler.java:43) at org.gradle.api.internal.tasks.compile.CompileJavaBuildOperationReportingCompiler$2.call(CompileJavaBuildOperationReportingCompiler.java:59) at org.gradle.api.internal.tasks.compile.CompileJavaBuildOperationReportingCompiler$2.call(CompileJavaBuildOperationReportingCompiler.java:51) at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:315) at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:305) at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:175) at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:101) at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36) at org.gradle.api.internal.tasks.compile.CompileJavaBuildOperationReportingCompiler.execute(CompileJavaBuildOperationReportingCompiler.java:51) at org.gradle.api.tasks.compile.JavaCompile.performCompilation(JavaCompile.java:154) at org.gradle.api.tasks.compile.JavaCompile.compile(JavaCompile.java:122) at com.android.build.gradle.tasks.AndroidJavaCompile.compile(AndroidJavaCompile.kt:214) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) at java.lang.reflect.Method.invoke(Method.java:498) at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:73) at org.gradle.api.internal.project.taskfactory.IncrementalTaskAction.doExecute(IncrementalTaskAction.java:47) at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:41) at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:28) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$2.run(ExecuteActionsTaskExecuter.java:284) at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:301) at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:293) at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:175) at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:91) at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:273) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:258) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.access$200(ExecuteActionsTaskExecuter.java:67) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$TaskExecution.execute(ExecuteActionsTaskExecuter.java:145) at org.gradle.internal.execution.impl.steps.ExecuteStep.execute(ExecuteStep.java:49) at org.gradle.internal.execution.impl.steps.CancelExecutionStep.execute(CancelExecutionStep.java:34) at org.gradle.internal.execution.impl.steps.TimeoutStep.executeWithoutTimeout(TimeoutStep.java:69) at org.gradle.internal.execution.impl.steps.TimeoutStep.execute(TimeoutStep.java:49) at org.gradle.internal.execution.impl.steps.CatchExceptionStep.execute(CatchExceptionStep.java:33) at org.gradle.internal.execution.impl.steps.CreateOutputsStep.execute(CreateOutputsStep.java:50) at org.gradle.internal.execution.impl.steps.SnapshotOutputStep.execute(SnapshotOutputStep.java:43) at org.gradle.internal.execution.impl.steps.SnapshotOutputStep.execute(SnapshotOutputStep.java:29) at org.gradle.internal.execution.impl.steps.CacheStep.executeWithoutCache(CacheStep.java:134) at org.gradle.internal.execution.impl.steps.CacheStep.lambda$execute$3(CacheStep.java:83) at java.util.Optional.orElseGet(Optional.java:267) at org.gradle.internal.execution.impl.steps.CacheStep.execute(CacheStep.java:82) at org.gradle.internal.execution.impl.steps.CacheStep.execute(CacheStep.java:36) at org.gradle.internal.execution.impl.steps.PrepareCachingStep.execute(PrepareCachingStep.java:33) at org.gradle.internal.execution.impl.steps.StoreSnapshotsStep.execute(StoreSnapshotsStep.java:38) at org.gradle.internal.execution.impl.steps.StoreSnapshotsStep.execute(StoreSnapshotsStep.java:23) at org.gradle.internal.execution.impl.steps.SkipUpToDateStep.executeBecause(SkipUpToDateStep.java:96) at org.gradle.internal.execution.impl.steps.SkipUpToDateStep.lambda$execute$0(SkipUpToDateStep.java:89) at java.util.Optional.map(Optional.java:215) at org.gradle.internal.execution.impl.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:52) at org.gradle.internal.execution.impl.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:36) at org.gradle.internal.execution.impl.DefaultWorkExecutor.execute(DefaultWorkExecutor.java:34) at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:91) ... 35 more
Java 编译器:(2 个错误，2 个警告)
Warning: The query returns some columns [invoice_id, terminal_no, cashier_name] which are not used by com.example.qrreceipt.Item. You can use @ColumnInfo annotation on the fields to specify the mapping. com.example.qrreceipt.Item has some fields [item_id, description, price] which are not returned by the query. If they are not supposed to be read from the result, you can mark them with @Ignore annotation. You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: invoice_id, terminal_no, cashier_name. Fields in com.example.qrreceipt.Item: item_id, description, price.
Error: The columns returned by the query does not have the fields [item_id,price] in com.example.qrreceipt.Item even though they are annotated as non-null or primitive. Columns returned by the query: [invoice_id,terminal_no,cashier_name]
Warning: The query returns some columns [invoice_id, terminal_no, cashier_name] which are not used by com.example.qrreceipt.Item. You can use @ColumnInfo annotation on the fields to specify the mapping. com.example.qrreceipt.Item has some fields [item_id, description, price] which are not returned by the query. If they are not supposed to be read from the result, you can mark them with @Ignore annotation. You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: invoice_id, terminal_no, cashier_name. Fields in com.example.qrreceipt.Item: item_id, description, price.
Error: error: The columns returned by the query does not have the fields [item_id,price] in com.example.qrreceipt.Item even though they are annotated as non-null or primitive. Columns returned by the query: [invoice_id,terminal_no,cashier_name]
最佳答案
创刊号
您当前的问题是您正在尝试从 Invoices 表中获取 Items。
这就是下面所说的:-
Error: The columns returned by the query does not have the fields [item_id,price] in com.example.qrreceipt.Item even though they are annotated as non-null or primitive. Columns returned by the query: [invoice_id,terminal_no,cashier_name]
修复此问题更改 发票道 使用:-
@Query("SELECT * FROM invoice WHERE invoice_id = :invoice_id")
List<Invoice> findInvoice(String invoice_id);
@Query("SELECT * FROM invoice")
List<Invoice> getAllInvoices();
List<Invoice> 而不是 List<Item> )其他问题
修复上述问题后，由于表定义与实体不匹配，您会遇到问题。
在那里面 :-
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`))");
@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;
}
}
关于java - 如何定义多个实体？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/56919832/