Android Room Java Inner Join with Count答案

【问题标题】：Android Room Java Inner Join with CountAndroid Room Java Inner Join with Count
【发布时间】：2020-01-11 07:38:23
【问题描述】：

我正在用 Java 编写一个 Android 应用，使用 Room 来管理数据。

我想返回一个数据库 (contacts_table) 中的所有项目以及另一个表 (emails_table) 中相关项目的相应计数，以便在回收站视图中使用。

即我希望用户在回收站视图的每个布局中查看他们有多少来自联系人的电子邮件。

当我测试运行我的应用时，我收到了这个错误：

error: There is a problem with the query: [SQLITE_ERROR] SQL error or missing database (no such table: emails_table)

在这行代码：

    @Query("SELECT  e.emails_count, c.* " +
            "FROM contacts_table c " +
            "INNER JOIN ( " +
            "   SELECT email_to, COUNT(email_to) emails_count " +
            "   FROM emails_table " +
            "   GROUP BY email_to) e " +
            "ON e.email_to = c.email_to")

我正在尝试做的事情可能吗？

contacts_table 实体：

@Entity(tableName = "contacts_table")
public class ContactEntity {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "email_token")
    private String emailToken;

    @ColumnInfo(name = "email_to")
    private String emailTo;

    private String password;

    @ColumnInfo(name = "contact_name")
    private String contactName;

    public ContactEntity(String emailToken, String password, String contactName) {
        this.emailToken = emailToken;
        this.password = password;
        this.contactName = contactName;
    }

    public int getId() {
        return id;
    }

    public String getEmailToken() {
        return emailToken;
    }

    public String getPassword() {
        return password;
    }

    public String getContactName() {
        return contactName;
    }

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

    public void setEmailToken(String emailToken) {
        this.emailToken = emailToken;
    }

    public void setPassword(String password) {
        this.password = password;
    }

    public void setContactName(String contactName) {
        this.contactName = contactName;
    }


    public String getEmailTo() {
        return emailTo;
    }

    public void setEmailTo(String emailTo) {
        this.emailTo = emailTo;
    }

}

contacts_dao：


import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface ContactsDao {
    @Insert(onConflict = OnConflictStrategy.IGNORE)
    void insert(ContactEntity contactEntity);

    @Update
    void update(ContactEntity contactEntity);

    @Delete
    void delete(ContactEntity contactEntity);
//
    @Query("SELECT  e.emails_count, c.* " +
            "FROM contacts_table c " +
            "INNER JOIN ( " +
            "   SELECT email_to, COUNT(email_to) emails_count " +
            "   FROM emails_table " +
            "   GROUP BY email_to) e " +
            "ON e.email_to = c.email_to")
    LiveData<List<ContactEntity>> getAllContacts();

    @Query("DELETE FROM contacts_table")
    void deleteAllContacts();

}

emails_table 实体：


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

import java.util.Date;
import java.sql.Time;

@Entity(tableName = "emails_table")
public class EmailEntity {

    @PrimaryKey(autoGenerate = true)
    private int id;

    @ColumnInfo(name = "email_from")
    private String emailFrom;

    @ColumnInfo(name = "email_to")
    private String emailTo;

    @ColumnInfo(name = "email_subject")
    private String emailSubject;

    @ColumnInfo(name = "email_body")
    private String emailBody;

    @ColumnInfo(name = "email_date")
    private Date dateReceived;

    @ColumnInfo(name = "email_time")
    private Time timeReceived;

    @ColumnInfo(name = "email_filename")
    private String filename;

    @ColumnInfo(name = "email_archive")
    private Boolean isArchived;

    @ColumnInfo(name = "email_token")
    private String emailToken;

    public EmailEntity(String emailFrom, String emailTo, String emailBody, Date dateReceived, Time timeReceived, String filename, Boolean isArchived, String emailSubject) {
        this.emailFrom = emailFrom;
        this.emailTo = emailTo;
        this.emailBody = emailBody;
        this.dateReceived = dateReceived;
        this.timeReceived = timeReceived;
        this.filename = filename;
        this.isArchived = isArchived;
        this.emailSubject = emailSubject;
    }

    public int getId() {
        return id;
    }

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

    public String getEmailFrom() {
        return emailFrom;
    }

    public void setEmailFrom(String emailFrom) {
        this.emailFrom = emailFrom;
    }

    public String getEmailTo() {
        return emailTo;
    }

    public void setEmailTo(String emailTo) {
        this.emailTo = emailTo;
    }

    public String getEmailBody() {
        return emailBody;
    }

    public void setEmailBody(String emailBody) {
        this.emailBody = emailBody;
    }

    public Date getDateReceived() {
        return dateReceived;
    }

    public void setDateReceived(Date dateReceived) {
        this.dateReceived = dateReceived;
    }

    public String getFilename() {
        return filename;
    }

    public void setFilename(String filename) {
        this.filename = filename;
    }

    public Boolean getArchived() {
        return isArchived;
    }

    public void setArchived(Boolean archived) {
        isArchived = archived;
    }

    public String getEmailToken() {
        return emailToken;
    }

    public void setEmailToken(String emailToken) {
        this.emailToken = emailToken;
    }

    public String getEmailSubject() {
        return emailSubject;
    }

    public void setEmailSubject(String emailSubject) {
        this.emailSubject = emailSubject;
    }


    public Time getTimeReceived() {
        return timeReceived;
    }

    public void setTimeReceived(Time timeReceived) {
        this.timeReceived = timeReceived;
    }
}

EmailsDao：


import androidx.lifecycle.LiveData;
import androidx.room.Dao;
import androidx.room.Delete;
import androidx.room.Insert;
import androidx.room.OnConflictStrategy;
import androidx.room.Query;
import androidx.room.Update;

import java.util.List;

@Dao
public interface EmailsDao {
    @Insert(onConflict = OnConflictStrategy.REPLACE)
    void insert(EmailEntity emailEntity);

    @Update
    void update(EmailEntity emailEntity);

    @Delete
    void delete(EmailEntity emailEntity);

    @Query("SELECT * FROM emails_table ORDER BY email_date")
    LiveData<List<EmailEntity>> getAllEmails();

    @Query("DELETE FROM emails_table")
    void deleteAllEmails();

}

电子邮件数据库


import android.content.Context;

import androidx.room.Database;
import androidx.room.Room;
import androidx.room.RoomDatabase;
import androidx.room.TypeConverters;
import com.xxxxxxxxxx.email_token.ui.contacts.ContactEntity;
import com.xxxxxxxxxx.email_token.ui.contacts.ContactsDao;


@Database(entities = {EmailEntity.class, ContactEntity.class}, version = 3)
@TypeConverters({DateConverter.class, TimeConverter.class})
public abstract class EmailsDatabase extends RoomDatabase {

    private static EmailsDatabase instance;

    public abstract EmailsDao emailsDao();
    public abstract ContactsDao contactsDao();
    public abstract HeaderDao headerDao();

    public static synchronized EmailsDatabase getInstance(Context context) {
        if (instance == null) {
            instance = Room.databaseBuilder(context.getApplicationContext(),
                    EmailsDatabase.class, "emails_database")
                    .fallbackToDestructiveMigration()
                    .build();
        }
        return instance;
    }

}

编辑 1：

这是构建输出中的堆栈轨迹：

Executing tasks: [:app:assembleDebug] in project /home/xxx/AndroidStudioProjects/email_token

> Task :app:preBuild UP-TO-DATE
> Task :app:preDebugBuild UP-TO-DATE
> Task :app:compileDebugAidl NO-SOURCE
> Task :app:checkDebugManifest UP-TO-DATE
> Task :app:generateDebugBuildConfig UP-TO-DATE
> Task :app:compileDebugRenderscript NO-SOURCE
> Task :app:javaPreCompileDebug UP-TO-DATE
> Task :app:mainApkListPersistenceDebug UP-TO-DATE
> Task :app:generateDebugResValues UP-TO-DATE
> Task :app:generateDebugResources UP-TO-DATE
> Task :app:mergeDebugResources UP-TO-DATE
> Task :app:createDebugCompatibleScreenManifests UP-TO-DATE
> Task :app:processDebugManifest
> Task :app:processDebugResources

> Task :app:compileDebugJavaWithJavac FAILED
/home/xxx/AndroidStudioProjects/email_token/app/src/main/java/com/xxxxxxxxxx/email_token/ui/email_messages/ContactsDao.java:31: error: There is a problem with the query: [SQLITE_ERROR] SQL error or missing database (no such table: emails_table)
    LiveData<List<ContactEntity>> getAllContacts();
                                  ^
1 error

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':app:compileDebugJavaWithJavac'.
> Compilation failed; see the compiler error output for details.

* Try:
Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Exception is:
org.gradle.api.tasks.TaskExecutionException: Execution failed for task ':app:compileDebugJavaWithJavac'.
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$3.accept(ExecuteActionsTaskExecuter.java:151)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$3.accept(ExecuteActionsTaskExecuter.java:148)
    at org.gradle.internal.Try$Failure.ifSuccessfulOrElse(Try.java:191)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:141)
    at org.gradle.api.internal.tasks.execution.ResolveBeforeExecutionStateTaskExecuter.execute(ResolveBeforeExecutionStateTaskExecuter.java:75)
    at org.gradle.api.internal.tasks.execution.ValidatingTaskExecuter.execute(ValidatingTaskExecuter.java:62)
    at org.gradle.api.internal.tasks.execution.SkipEmptySourceFilesTaskExecuter.execute(SkipEmptySourceFilesTaskExecuter.java:108)
    at org.gradle.api.internal.tasks.execution.ResolveBeforeExecutionOutputsTaskExecuter.execute(ResolveBeforeExecutionOutputsTaskExecuter.java:67)
    at org.gradle.api.internal.tasks.execution.ResolveAfterPreviousExecutionStateTaskExecuter.execute(ResolveAfterPreviousExecutionStateTaskExecuter.java:46)
    at org.gradle.api.internal.tasks.execution.CleanupStaleOutputsExecuter.execute(CleanupStaleOutputsExecuter.java:94)
    at org.gradle.api.internal.tasks.execution.FinalizePropertiesTaskExecuter.execute(FinalizePropertiesTaskExecuter.java:46)
    at org.gradle.api.internal.tasks.execution.ResolveTaskExecutionModeExecuter.execute(ResolveTaskExecutionModeExecuter.java:95)
    at org.gradle.api.internal.tasks.execution.SkipTaskWithNoActionsExecuter.execute(SkipTaskWithNoActionsExecuter.java:57)
    at org.gradle.api.internal.tasks.execution.SkipOnlyIfTaskExecuter.execute(SkipOnlyIfTaskExecuter.java:56)
    at org.gradle.api.internal.tasks.execution.CatchExceptionTaskExecuter.execute(CatchExceptionTaskExecuter.java:36)
    at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter$1.executeTask(EventFiringTaskExecuter.java:73)
    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:416)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102)
    at org.gradle.internal.operations.DelegatingBuildOperationExecutor.call(DelegatingBuildOperationExecutor.java:36)
    at org.gradle.api.internal.tasks.execution.EventFiringTaskExecuter.execute(EventFiringTaskExecuter.java:49)
    at org.gradle.execution.plan.LocalTaskNodeExecutor.execute(LocalTaskNodeExecutor.java:43)
    at org.gradle.execution.taskgraph.DefaultTaskExecutionGraph$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$1.run(ManagedExecutorImpl.java:46)
    at org.gradle.internal.concurrent.ThreadFactoryImpl$ManagedThreadRunnable.run(ThreadFactoryImpl.java:55)
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:60)
    at org.gradle.api.internal.tasks.compile.incremental.IncrementalResultStoringCompiler.execute(IncrementalResultStoringCompiler.java:44)
    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:416)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$CallableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:406)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.call(DefaultBuildOperationExecutor.java:102)
    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:237)
    at org.gradle.internal.reflect.JavaMethod.invoke(JavaMethod.java:103)
    at org.gradle.api.internal.project.taskfactory.IncrementalTaskInputsTaskAction.doExecute(IncrementalTaskInputsTaskAction.java:46)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:41)
    at org.gradle.api.internal.project.taskfactory.AbstractIncrementalTaskAction.execute(AbstractIncrementalTaskAction.java:25)
    at org.gradle.api.internal.project.taskfactory.StandardTaskAction.execute(StandardTaskAction.java:28)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$5.run(ExecuteActionsTaskExecuter.java:404)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:402)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$RunnableBuildOperationWorker.execute(DefaultBuildOperationExecutor.java:394)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor$1.execute(DefaultBuildOperationExecutor.java:165)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:250)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.execute(DefaultBuildOperationExecutor.java:158)
    at org.gradle.internal.operations.DefaultBuildOperationExecutor.run(DefaultBuildOperationExecutor.java:92)
    at org.gradle.internal.operations.DelegatingBuildOperationExecutor.run(DelegatingBuildOperationExecutor.java:31)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeAction(ExecuteActionsTaskExecuter.java:393)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.executeActions(ExecuteActionsTaskExecuter.java:376)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.access$200(ExecuteActionsTaskExecuter.java:80)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter$TaskExecution.execute(ExecuteActionsTaskExecuter.java:213)
    at org.gradle.internal.execution.steps.ExecuteStep.lambda$execute$0(ExecuteStep.java:32)
    at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:32)
    at org.gradle.internal.execution.steps.ExecuteStep.execute(ExecuteStep.java:26)
    at org.gradle.internal.execution.steps.CleanupOutputsStep.execute(CleanupOutputsStep.java:58)
    at org.gradle.internal.execution.steps.CleanupOutputsStep.execute(CleanupOutputsStep.java:35)
    at org.gradle.internal.execution.steps.ResolveInputChangesStep.execute(ResolveInputChangesStep.java:48)
    at org.gradle.internal.execution.steps.ResolveInputChangesStep.execute(ResolveInputChangesStep.java:33)
    at org.gradle.internal.execution.steps.CancelExecutionStep.execute(CancelExecutionStep.java:39)
    at org.gradle.internal.execution.steps.TimeoutStep.executeWithoutTimeout(TimeoutStep.java:73)
    at org.gradle.internal.execution.steps.TimeoutStep.execute(TimeoutStep.java:54)
    at org.gradle.internal.execution.steps.CatchExceptionStep.execute(CatchExceptionStep.java:35)
    at org.gradle.internal.execution.steps.CreateOutputsStep.execute(CreateOutputsStep.java:51)
    at org.gradle.internal.execution.steps.SnapshotOutputsStep.execute(SnapshotOutputsStep.java:45)
    at org.gradle.internal.execution.steps.SnapshotOutputsStep.execute(SnapshotOutputsStep.java:31)
    at org.gradle.internal.execution.steps.CacheStep.executeWithoutCache(CacheStep.java:201)
    at org.gradle.internal.execution.steps.CacheStep.execute(CacheStep.java:70)
    at org.gradle.internal.execution.steps.CacheStep.execute(CacheStep.java:45)
    at org.gradle.internal.execution.steps.BroadcastChangingOutputsStep.execute(BroadcastChangingOutputsStep.java:49)
    at org.gradle.internal.execution.steps.StoreSnapshotsStep.execute(StoreSnapshotsStep.java:43)
    at org.gradle.internal.execution.steps.StoreSnapshotsStep.execute(StoreSnapshotsStep.java:32)
    at org.gradle.internal.execution.steps.RecordOutputsStep.execute(RecordOutputsStep.java:38)
    at org.gradle.internal.execution.steps.RecordOutputsStep.execute(RecordOutputsStep.java:24)
    at org.gradle.internal.execution.steps.SkipUpToDateStep.executeBecause(SkipUpToDateStep.java:96)
    at org.gradle.internal.execution.steps.SkipUpToDateStep.lambda$execute$0(SkipUpToDateStep.java:89)
    at org.gradle.internal.execution.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:54)
    at org.gradle.internal.execution.steps.SkipUpToDateStep.execute(SkipUpToDateStep.java:38)
    at org.gradle.internal.execution.steps.ResolveChangesStep.execute(ResolveChangesStep.java:77)
    at org.gradle.internal.execution.steps.ResolveChangesStep.execute(ResolveChangesStep.java:37)
    at org.gradle.internal.execution.steps.legacy.MarkSnapshottingInputsFinishedStep.execute(MarkSnapshottingInputsFinishedStep.java:36)
    at org.gradle.internal.execution.steps.legacy.MarkSnapshottingInputsFinishedStep.execute(MarkSnapshottingInputsFinishedStep.java:26)
    at org.gradle.internal.execution.steps.ResolveCachingStateStep.execute(ResolveCachingStateStep.java:90)
    at org.gradle.internal.execution.steps.ResolveCachingStateStep.execute(ResolveCachingStateStep.java:48)
    at org.gradle.internal.execution.impl.DefaultWorkExecutor.execute(DefaultWorkExecutor.java:33)
    at org.gradle.api.internal.tasks.execution.ExecuteActionsTaskExecuter.execute(ExecuteActionsTaskExecuter.java:120)
    ... 35 more


* Get more help at https://help.gradle.org

BUILD FAILED in 7s
10 actionable tasks: 3 executed, 7 up-to-date

【问题讨论】：

标签： java join count android-room

【解决方案1】：

获取您的代码并使用它运行它（没有 LiveData 和类型转换器（使用字符串而不是日期和时间类型））：-

emailsDatabase = Room.databaseBuilder(this,EmailsDatabase.class,"emailsdb")
                .allowMainThreadQueries()
                .build();

        ContactEntity c1 = new ContactEntity("email1","password","Fred");
        c1.setEmailTo("email1");
        ContactEntity c2 = new ContactEntity("email2","password","Mary");
        c2.setEmailTo("email2");
        ContactEntity c3 = new ContactEntity("email3","password","Jane");
        c3.setEmailTo("email3");
        emailsDatabase.contactsDao().insert(c1);
        emailsDatabase.contactsDao().insert(c2);
        emailsDatabase.contactsDao().insert(c3);
        emailsDatabase.emailsDao().insert(
                new EmailEntity(
                        "email1",
                        "email2",
                        "Blah",
                        "2019-12-31",
                        "10:30","filex",
                        false,
                        "This")
        );
        emailsDatabase.emailsDao().insert(
                new EmailEntity(
                        "email1",
                        "email3",
                        "Blah",
                        "2019-12-31",
                        "10:30","filex",
                        false,
                        "This")
        );
        emailsDatabase.emailsDao().insert(
                new EmailEntity(
                        "email2",
                        "email1",
                        "Blah",
                        "2019-12-31",
                        "10:30","filex",
                        false,
                        "This")
        );
        emailsDatabase.emailsDao().insert(
                new EmailEntity(
                        "email1",
                        "email2",
                        "Blah",
                        "2019-12-31",
                        "10:40","filex",
                        false,
                        "This")
        );
        List<EmailEntity> emailEntityList = emailsDatabase.emailsDao().getAllEmails();
        for (EmailEntity e: emailEntityList) {
            logEmail(e);
        }
        List<ContactEntity> contactEntityList = emailsDatabase.contactsDao().getAllContacts();
        for (ContactEntity c: contactEntityList) {
            logContact(c);
        }
        List<ContactWithEmailCounts> contactWithEmailCountsList = emailsDatabase.contactsDao().testit();
        for (ContactWithEmailCounts cwec: contactWithEmailCountsList) {
            Log.d("CWECINFO","Email Count = " + cwec.emailcount);
        }
    }

    private void logEmail(EmailEntity e) {
        Log.d("EMAIlINFO","Email From = " + e.getEmailFrom() + "Email To " + e.getEmailTo() + "Email Token = " + e.getEmailToken());
    }
    private void logContact(ContactEntity c) {
        Log.d("CONTACTINFO","Name = " + c.getContactName() + " Email = " + c.getEmailToken());
    }

还有一个类：-

public class ContactWithEmailCounts {

    @Embedded
    ContactEntity contactEntity;
    int emailcount;
}

添加到 ContactsDao 的查询为（即除了添加的要调用的方法之外未更改）：-

@Query("SELECT  e.emails_count AS emailcount, c.* " +
        "FROM contacts_table c " +
        "INNER JOIN ( " +
        "   SELECT email_to, COUNT(email_to) emails_count " +
        "   FROM emails_table " +
        "   GROUP BY email_to) e " +
        "ON e.email_to = c.email_to")
List<ContactWithEmailCounts> testit();

然后我得到以下结果（即@Query 工作而不是失败）：-

2020-01-11 20:36:37.439 D/EMAIlINFO: Email From = email1Email To email2Email Token = null
2020-01-11 20:36:37.439 D/EMAIlINFO: Email From = email1Email To email3Email Token = null
2020-01-11 20:36:37.439 D/EMAIlINFO: Email From = email2Email To email1Email Token = null
2020-01-11 20:36:37.439 D/EMAIlINFO: Email From = email1Email To email2Email Token = null
2020-01-11 20:36:37.440 D/CONTACTINFO: Name = Fred Email = email1
2020-01-11 20:36:37.441 D/CONTACTINFO: Name = Mary Email = email2
2020-01-11 20:36:37.441 D/CONTACTINFO: Name = Jane Email = email3
2020-01-11 20:36:37.442 D/CWECINFO: Email Count = 1
2020-01-11 20:36:37.442 D/CWECINFO: Email Count = 2
2020-01-11 20:36:37.442 D/CWECINFO: Email Count = 1

因此，我怀疑未找到的表到底是什么，即由于某种原因该表不存在，也许它与您的测试运行方式有关。

【讨论】：

嘿迈克！感谢您对其进行测试并提供反馈。我的测试是在 SDK 的模拟器中运行应用程序，不是很健壮。我应该更多地研究如何运行测试吗？这是我的“我想学习如何编写应用程序”项目，第一次用 java 编写，如果我的问题似乎没有受过教育，很抱歉 - 这是因为它们是。
@RexB 简而言之，我看不出给出的代码有任何错误，我也看不出在典型用法下你会如何得到这样的错误，因为如果表没有，Room 会抛出异常' t 存在或无法创建（我看不到任何拼写错误，也没有使用您的代码显示一个）。就好像在房间建立数据库之后表已经被删除了。所以我的意思是问题似乎出在代码运行的其他地方。首先是将堆栈跟踪添加到问题中，而不仅仅是堆栈跟踪中的单个消息。
我已经用构建过程的堆栈跟踪输出更新了我的问题
@RexB 尝试重建项目，同时确保您使用的是最新的 Room 库（以防万一我认为是 2.2.3）。
我的 build.gradle(Module: app) 文件有这个：
def room_version = "2.2.3"
implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"