Room Persistence: Error:Entities and Pojos must ha

问题:

I'm converting a project to Kotlin and I'm trying to make my model (which is also my entity) a data class I intend to use Moshi to convert the JSON responses from the API

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int,
    var title: String,
    var overview: String,
    var poster_path: String,
    var backdrop_path: String,
    var release_date: String,
    var vote_average: Double,
    var isFavorite: Int
)

I can't build the app cause of the following error

Entities and Pojos must have a usable public constructor. You can have an empty constructor or a constructor whose parameters match the fields (by name and type). Cannot find setter for field.

The examples I found are not far from this

Ideas on how to solve it?

回答1:

Had a similar issue before.

First I've updated/added apply plugin: 'kotlin-kapt' to gradle.

Next, I've used it instead of annotationProcessor in gradle:

kapt "android.arch.persistence.room:compiler:1.0.0-alpha4"

Tha last thing was to create an immutable data class:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    val id : Int,
    val title: String,
    val overview: String,
    val poster_path: String,
    val backdrop_path: String,
    val release_date: String,
    val vote_average: Double,
    val isFavorite: Int
)

UPDATE:

This solution works when you have classes for the model and classes for Database in the same Android Module. If you have model classes in Android Library module and the rest of the code in your main module, Room will NOT recognize them.

回答2:

you need to specify a secondary constructor like so:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int,
    var title: String,
    var overview: String,
    var poster_path: String,
    var backdrop_path: String,
    var release_date: String,
    var vote_average: Double,
    var isFavorite: Int
) {
    constructor() : this(0, "", "", "", "", "", 0.0, 0)
}    

回答3:

It's not a problem in your case, but for others, this error can occur if you have @Ignore params in your constructor, i.e. Room expects to have either:

• parameterless constructor or
• constructor with all fields not marked with @Ignore

for example:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int,
    var title: String,
    @Ignore var overview: String) 

will not work. This will:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int,
    var title: String) 

回答4:

What worked for me:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int? = 0,
    var title: String? = "",
    var overview: String? = "",
    var poster_path: String? = "",
    var backdrop_path: String? = "",
    var release_date: String? = "",
    var vote_average: Double? = 0.0,
    var isFavorite: Int? = 0
)

回答5:

For me all I had to do was to add a constructor to the data class with empty params sent to it like so:

    @Entity(tableName = "posts")
data class JobPost(
    @Ignore
    @SerializedName("companyLogo")
    var companyLogo: String,
    @Ignore
    @SerializedName("companyName")
    var companyName: String,
    @Ignore
    @SerializedName("isAggregated")
    var isAggregated: String,
    @PrimaryKey(autoGenerate = false)
    @SerializedName("jobID")
    var jobID: String,
    @Ignore
    @SerializedName("jobTitle")
    var jobTitle: String,
    @Ignore
    @SerializedName("postedOn")
    var postedOn: String,
    @Ignore
    @SerializedName("region")
    var region: String
) {
    constructor() : this("","","","","","","")
}

回答6:

I think that a good option for resolve it is:

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int = 0,
    var title: String = "",
    var overview: String = "",
    var poster_path: String = "",
    var backdrop_path: String = "",
    var release_date: String = "",
    var vote_average: Double = 0.0,
    var isFavorite: Int = 0
)

回答7:

Kotlin allows long as a parameter name, but this won't work when room generates java code.

回答8:

I also had this issue, but i realized the problem was that i added the @Embedded annotation to a property that already had a type converter, so anyone having the same problem should check the property declarations for your model class carefully and make sure the @Embedded annotation is not on a property that has a type converter associated with it.

回答9:

It turned out to be a bug on the library https://github.com/googlesamples/android-architecture-components/issues/49

回答10:

https://issuetracker.google.com/issues/62851733

i found this is @Relation's projection bug! not Kotlin language problem. based google GithubBrowserSample java also happend error, but different error message.

below is my kotlin code:

data class UserWithCommunities(
        @Embedded
        var user: User = User(0, null),

        @Relation(parentColumn = "id",
                entityColumn = "users_id",
                entity = CommunityUsers::class,
                projection = arrayOf("communities_id")) // delete this line.
        var communityIds: List<Int> = emptyList()
)

right:

data class UserWithCommunities(
        @Embedded
        var user: User = User(0, null),

        @Relation(parentColumn = "id",
                entityColumn = "users_id",
                entity = CommunityUsers::class)
        var communityList: List<CommunityUsers> = emptyList()
)

回答11:

I had this problem with an entity (all fields were properly-initialized vars like a lot of the answers here are suggesting) that included a list of related, non-primitive items like the OP in this SO question had. For example:

@Entity(tableName = "fruits")
data class CachedFruitEntity(
        @PrimaryKey var id: Long = 0L,
        @Embedded(prefix = "buyer_") var buyerEntity: CachedBuyerEntity? = null
        @TypeConverters(VendorsConverter::class)
        var vendorEntities: List<CachedVendorEntity?> = listOf()))

That is, it has an embedded field, and it took me a while to realize that what I actually needed was a type converter for the vendor entity list instead (the compiler wasn't throwing the usual Error:(58, 31) error: Cannot figure out how to save this field into database. You can consider adding a type converter for it. So my solution was very similar to this answer

This google architecture components github thread has more info on this misleading error, but not sure if the issue has been fixed yet.

回答12:

Same bug, much stranger solution: Do not return cursor using reactivex Maybe<Cursor> on your Dao. Flowable, Single, and Observable did not work either.

Simply bite the bullet and make the reactive call outside the Dao request. Before:

@Dao
interface MyDao{
    @Query("SELECT * FROM mydao")
    fun getCursorAll(): Flowable<Cursor>
}

After:

@Dao
interface MyDao{
    @Query("SELECT * FROM mydao")
    fun getCursorAll(): Cursor
}

Meta:

Android Studio 3.2
Build #AI-181.5540.7.32.5014246, built on September 17, 2018
JRE: 1.8.0_152-release-1136-b06 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.12.6

回答13:

Don't use to dataclass,use normal class instead. This method will solve problem

回答14:

To expand on the answers provided by @evanchooly and @daneejela, you need a secondary constructor to be able to use @Ignore parameters in your primary constructor. This is so Room still has a constructor that it can use when instantiating your object. Per your example, if we ignore one of the fields:

@Entity(tableName = "movies")
data class MovieKt(
        @PrimaryKey
        var id : Int,
        var title: String,
        var overview: String,
        var poster_path: String,
        var backdrop_path: String,
        @Ignore var release_date: String,
        @Ignore var vote_average: Double,
        @Ignore var isFavorite: Int
) {
    constructor(id: Int, title: String, overview: String, poster_path: String, backdrop_path: String) {
        this(id, title, overview, poster_path, backdrop_path, "", 0.0, 0)
    }
}

回答15:

I had the same issue. You can move the @Ignore fields to class body. For example :

@Entity(tableName = "movies")
data class MovieKt(
    @PrimaryKey
    var id : Int,
    var title: String) {
    @Ignore var overview: String
} 

回答16:

Just add the below annotation to any constructor that causes the errors and add a new blank constructor.

@Ignore

回答17:

As stated in Room Database Entity:

Each entity must either have a no-arg constructor or a constructor whose parameters match fields (based on type and name).

So adding an empty constructor and annotating your parameterized constructor with @Ignore will solve your problem. An example:

public class POJO {

    long id;

    String firstName;

    @Ignore
    String lastName;

    public POJO() {
    }

    @Ignore
    public POJO(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    // getters and setters
    // ...

}

回答18:

With 2.1.0-alpha6, it turned out to be an invalid return type in Dao. Fixing the return type as expected fixed it.

回答19:

For me, I was using 'lat' & 'long' as a variable name in the data(Entity) class for kotlin so renaming to latitude & longitude it worked.

Not working:

@Entity(tableName = "table_User")
data class User(@PrimaryKey var userId : Int, @ColumnInfo(name = "first_name") 
var firstName: String
            , @ColumnInfo(name = "last_name") var lastName: String
            , @ColumnInfo(name = "password") var password: String
            , @ColumnInfo(name = "dob") var dob: Long
            , @ColumnInfo(name = "address") var address: String
            , @ColumnInfo(name = "lat") var latitude: Double
            , @ColumnInfo(name = "long") var longitude: Double) {

}

Working:

@Entity(tableName = "table_User")
data class User(@PrimaryKey var userId : Int, @ColumnInfo(name = "first_name") 
var firstName: String
            , @ColumnInfo(name = "last_name") var lastName: String
            , @ColumnInfo(name = "password") var password: String
            , @ColumnInfo(name = "dob") var dob: Long
            , @ColumnInfo(name = "address") var address: String
            , @ColumnInfo(name = "latitude") var latitude: Double
            , @ColumnInfo(name = "longitude") var longitude: Double) {

}

回答20:

For a variation on FutureShocked answer that implements autoGenerate:

@Entity(tableName = "movies")
data class MovieKt(
        var title: String,
        var overview: String,
        var poster_path: String,
        var backdrop_path: String,
        @Ignore var release_date: String,
        @Ignore var vote_average: Double,
        @Ignore var isFavorite: Int
) {
@PrimaryKey(autoGenerate = true) var id : Int = 0

    constructor(title: String, overview: String, poster_path: String, backdrop_path: String) {
        this(id, title, overview, poster_path, backdrop_path, "", 0.0, 0)
    }
}