CrimeDao can't be built witih suspend functions

Android Programming (5th Edition) 14. Databases and the Room Library
1

Using the eBook, PDF, I’m following all the instructions in chapter 12: “Coroutines and Databases”. I’ve gotten all the way through defining the CriminalIntentApplication object and adding it to the manifest. But what I go to build…

With CrimeDao defined as this:

package com.selbie.criminalintent.CrimeDatabase
import androidx.room.Dao
import androidx.room.Query
import com.selbie.criminalintent.Crime
import java.util.*

@Dao
interface CrimeDao {
    @Query("SELECT * from crime")
    suspend fun getCrimes() : List<Crime>

    @Query("SELECT * FROM crime WHERE id=(:id)")
    suspend fun getCrime(id: UUID):Crime
}

I get a lot of errors as shown below. I found a Stack Overflow article saying Dao’s can’t contain suspend functions. So I removed suspend keyword from each and it builds fine. Is there something I missed? I’m specifying id 'org.jetbrains.kotlin.kapt' version '1.6.10' apply false in the build.gradle as well as version 2.4.2 for the three Room dependencies the eBook instructed me to add.

Is there a fix such that Dao functions can have suspend functions? If I remove suspend from these function declarations, will that block me later?

C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:11: error: Not sure how to convert a Cursor to this method's return type (java.lang.Object).
    public abstract java.lang.Object getCrimes(@org.jetbrains.annotations.NotNull()
                                     ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:12: error: Query method parameters should either be a type that can be converted into a database column or a List / Array that contains such type. You can consider adding a Type Adapter for this.
    kotlin.coroutines.Continuation<? super java.util.List<com.selbie.criminalintent.Crime>> continuation);
                                                                                            ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:11: error: Unused parameter: continuation
    public abstract java.lang.Object getCrimes(@org.jetbrains.annotations.NotNull()
                                     ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:16: error: Not sure how to convert a Cursor to this method's return type (java.lang.Object).
    public abstract java.lang.Object getCrime(@org.jetbrains.annotations.NotNull()
                                     ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:18: error: Query method parameters should either be a type that can be converted into a database column or a List / Array that contains such type. You can consider adding a Type Adapter for this.
    kotlin.coroutines.Continuation<? super com.selbie.criminalintent.Crime> continuation);
                                                                            ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:16: error: Unused parameter: continuation
    public abstract java.lang.Object getCrime(@org.jetbrains.annotations.NotNull()
                                     ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:11: warning: The query returns some columns [id, title, date, isSolved, requiredPolice] which are not used by java.lang.Object. You can use @ColumnInfo annotation on the fields to specify the mapping. You can annotate the method with @RewriteQueriesToDropUnusedColumns to direct Room to rewrite your query to avoid fetching unused columns.  You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: id, title, date, isSolved, requiredPolice.
    public abstract java.lang.Object getCrimes(@org.jetbrains.annotations.NotNull()
                                     ^
C:\Users\jselbie\source\repos\AndroidStudioProjects\CriminalIntent\app\build\tmp\kapt3\stubs\debug\com\selbie\criminalintent\CrimeDatabase\CrimeDao.java:16: warning: The query returns some columns [id, title, date, isSolved, requiredPolice] which are not used by java.lang.Object. You can use @ColumnInfo annotation on the fields to specify the mapping. You can annotate the method with @RewriteQueriesToDropUnusedColumns to direct Room to rewrite your query to avoid fetching unused columns.  You can suppress this warning by annotating the method with @SuppressWarnings(RoomWarnings.CURSOR_MISMATCH). Columns returned by the query: id, title, date, isSolved, requiredPolice.
    public abstract java.lang.Object getCrime(@org.jetbrains.annotations.NotNull()
2

Can you share the list of dependencies in the app/build.gradle file? I want to make sure you have the coroutines library in there.

3

To solve this problem, you can use the room-ktx library, which provides support for suspend functions. To do this, you need to make the following changes:
In the build.gradle file, add a dependency on room-ktx:
implementation “androidx.room:room-ktx:2.4.2”
Change the declaration of functions in the CrimeDao interface to use Flow instead of suspend:
@Query(“SELECT * from crime”)
fun getCrimes(): Flow<List>

@Query(“SELECT * FROM crime WHERE id=(:id)”)
fun getCrime(id: UUID): Flow.
Notice that the return types are now changed to Flow<List> and Flow, respectively.

After making these changes, Room will convert query results correctly and notify you of any data changes.

Good luck with developing your application!