I'm making an Workout log app.
One Workout has multiple sets.
I want to store this in a one-to-many relationship in Room.
In conclusion, I succeeded in saving, but I'm not sure what one class does.
All of the other example sample code uses this class, so I made one myself, but it doesn't tell me what it means.
WorkoutWithSets
data class WorkoutWithSets(
#Embedded val workout: Workout,
#Relation (
parentColumn = "workoutId",
entityColumn = "parentWorkoutId"
)
val sets: List<WorkoutSetInfo>
)
The following two entity classes seem to be sufficient to express a one-to-many relationship. (Stored in Room)
Workout
#Entity
data class Workout(
#PrimaryKey(autoGenerate = true)
var workoutId: Long = 0,
var title: String = "",
var memo: String = "",
)
It seems that the following two entity classes are sufficient enough to store a one-to-many relationship.. (stored in Room)
WorkoutSetInfo
#Entity(
foreignKeys = [
ForeignKey(
entity = Workout::class,
parentColumns = arrayOf("workoutId"),
childColumns = arrayOf("parentWorkoutId"),
onDelete = ForeignKey.CASCADE
)
]
)
data class WorkoutSetInfo(
#PrimaryKey(autoGenerate = true)
val id: Long = 0,
val set: Int,
var weight: String = "",
var reps: String = "",
var unit: WorkoutUnit = WorkoutUnit.kg,
val parentWorkoutId: Long = 0
)
Even if the WorkoutWithSet class does not exist, the Workout and WorkoutSetInfo classes are stored in Room.
What does WorkoutWithSets class mean? (or where should I use it?)
What does WorkoutWithSets class mean?
It is a class that can be used to retrieve a Workout along with all the related WorkoutSetInfos via a simple #Query that just retrieves the parent Workouts.
What Room does is add an additional query that retrieves the children (WorkoutSetInfo's) for each Workout.
The result being a list of WorkOutWithSets each element (a Workout) containing/including a list of all the related WorkoutSetInfo's.
You would use this when you want to process a Workout (or many Workouts) along with the related WorkoutSetInfo's (aka the child WorkoutSetInfo's for the parent Workout).
What Room does is consider the type (objects) to be returned.
So if you had
#Query("SELECT * FROM workout")
fun getJustWorkouts(): List<Workout>
then the function would return just a list of Workout objects.
But if you had
#Query("SELECT * FROM workout")
fun getWorkoutsWithSets(): List<WorkoutWithSets>
then the function would return a list of WorkoutWithSets and thus the parent Workouts with the child WorkoutSetInfo's.
What Room does is build and execute an underlying query, for eack Workout extracted, along the lines of "SELECT * FROM workoutInfoSet WHERE workout.workoutId = parentWorkoutId" and hence why it suggests the use of the #Transaction annotation (the build will include a warning if #Transaction is not coded).
I have a Json similar to below format:
{
"gender": "male",
"name": {
"first": "Axel",
"last": "Raab"
}
}
I want to create 2 tables, say Person and Name and store this data in these 2 tables.
My Entity classes look like these:
#Entity
data class Person(
#PrimaryKey(autoGenerate = true)
var pid: Int,
#SerializedName("gender")
var gender: String?,
#SerializedName("name")
#Ignore
var name: Name?,
)
#Entity(indices = [Index("pId")],
foreignKeys = [ForeignKey(
entity = Person::class,
parentColumns = ["pid"],
childColumns = ["pId"],
onDelete = ForeignKey.CASCADE)])
data class Name(
#PrimaryKey(autoGenerate = true)
val mId: Int,
#SerializedName("first")
var first: String?,
#SerializedName("last")
var last: String?,
var pId: Int
)
I have created corresponding Daos but unable to identify a way where I can write a transaction that would store this data into 2 tables and relate then using provided ids.
I have gone through many solutions that would either use #Embedded or #Relation or TypeConverter approaches but either they do not fit my use case or the solution is about querying the data and not how to save or insert.
Thanks.
You can use Embedded
e.g
public class Coordinates {
double latitude;
double longitude;
}
public class Address {
String street;
#Embedded
Coordinates coordinates;
}
Insert example in your DAO
#Insert
fun insert(item: Coordinates)
you can pass Coordinates instance variable in your insert function
Address("your street", Coordinates(your_lat,your_lng))
I have a Many to Many relationship set up on my Room database denoted by the following diagram:
eveything works great but I would like to make the following addition:
My question is how do I go about having RecipeWithIngredients get this unit:String variable from the RecipeIngredientRef Entity when a recipeWithIngredients is constructed on a query?
#Entity(indices = [Index(value = ["name"],unique = true)])
data class Recipe(
var name: String,
val image: String?
) {
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "recipeID")
var ID: Long = 0
}
#Entity(indices = [Index(value = ["name"],unique = true)])
data class Ingredient(
val name: String,
val image: String?,
val amount: Int
) {
#PrimaryKey(autoGenerate = true)
#ColumnInfo(name = "ingredientID")
var ID: Long = 0
}
#Entity(primaryKeys = ["recipeID", "ingredientID"])
data class RecipeIngredientRef(
val recipeID: Long,
val ingredientID: Long,
val unit: String
)
data class RecipeWithIngredients(
#Embedded
val recipe: Recipe,
#Relation(
parentColumn = "recipeID",
entity = Ingredient::class,
entityColumn = "ingredientID",
associateBy = Junction(
value = RecipeIngredientRef::class,
parentColumn = "recipeID",
entityColumn = "ingredientID"
)
)
val ingredients: List<Ingredient>
)
As far as I know there is no built-in way using current many-to-many Relations in Room for that. So I just want to save your time for researches.
This RecipeIngredientRef table is used internally just for two other tables' join and for now adding there additional fields will not help to get these fields with #Relations/Junction mechanism.
You can try workarounds, but they are no so elegant and they needed to dig deeper into Room's result's processing:
Don't use #Relation/Junction mechanism for RecipeWithIngridients at all, write your own query with two JOINs (since you should get data from 3 tables). As a result you'll get some raw set of records and then you should use loops and methods of Kotlin collections to turn result into needed form.
Use #Relation/Junction mechanism, but after getting result - make additional processing of result - make one more query to RecipeIngredientRef table and set missing unit value manually (again with loops and methods of Kotlin collections).
I've this json :
{
"products": [{
"id": "150",
"num": "7",
"name": "450 SA"
}, {
"id": "122",
"num": "13",
"name": "Gillette Blue"
}]}
I've created my models from it , i've these classes for it :
#Entity
data class ProductsModel(
#Json(name = "products")
val products: List<Product>
)
#Entity
data class Product(
#PrimaryKey(autoGenerate = false)
val id: String,
#Json(name = "name")
val name: String,
#Json(name = "num")
val num: String,
)
this is my DAO class for inserting data into my room database :
#Dao
interface ProductsDAO {
// 2: Insert
#Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(product: ProductsModel)
When I want to run the application , I get this error :
error: Cannot figure out how to save this field into database. You can consider adding a type converter for it.
How can I save these data into my database ?
Room provides functionality for converting between primitive and boxed types but doesn't allow for object references between entities.
You can simply create a table that has 3 columns - id, name and num. So each row would be a different Product
OR
Your data base should only save the list of Product's and you should provide a TypeConverter, which converts a Product class to and from a known type that Room can persist.
more about type converters - link
The original question is at the very bottom. I have created a minimal (non-)working example of my problem which is hopefully easier to read through. The example is here at gitlab. There is a readme describing the problem. I am pasting some parts of the project here.
The data model is plain simple:
Owner <--(1:N)-- Child --(N:1)--> ReferencedByChild
All I want to do is to read an Owner from the database with all its associated Child objects and for each Child object
also the ReferencedByChild object that it references.
The whole code that reproduces my problem is below. What I am not 100% sure about is the #Relation on the OwnerWithEverything POJO. See below please.
#Database(
entities = [
Owner::class,
Child::class,
ReferencedByChild::class
],
version = 1
)
abstract class AppDatabase : RoomDatabase() {
abstract fun appDao(): AppDao
}
#Dao
abstract class AppDao {
#Insert
abstract fun insertOwner(owner: Owner): Long
#Insert
abstract fun insertChild(child: Child): Long
#Insert
abstract fun insertReferencedByChild(referencedByChild: ReferencedByChild): Long
#Query("SELECT * FROM Child INNER JOIN ReferencedByChild ON Child.referencedByChildId = ReferencedByChild.refByChildId ORDER BY Child.childText")
abstract fun findAllChildrenWithReferencedClasses(): List<ChildWithReferenced>
// Commenting this query out makes the build pass, so something here is incorrect.
#Query("SELECT * FROM Owner")
abstract fun findOwnersWithEverything(): List<OwnerWithEverything>
}
// ENTITIES
#Entity
data class Owner(
#PrimaryKey(autoGenerate = true)
val ownerId: Long,
val ownerText: String
)
#Entity(
foreignKeys = [
ForeignKey(
entity = Owner::class,
parentColumns = arrayOf("ownerId"),
childColumns = arrayOf("referencedOwnerId"),
onDelete = ForeignKey.CASCADE
),
ForeignKey(
entity = ReferencedByChild::class,
parentColumns = arrayOf("refByChildId"),
childColumns = arrayOf("referencedByChildId"),
onDelete = ForeignKey.CASCADE
)
]
)
data class Child(
#PrimaryKey(autoGenerate = true)
val childId: Long,
val childText: String,
val referencedOwnerId: Long,
val referencedByChildId: Long
)
#Entity
data class ReferencedByChild(
#PrimaryKey(autoGenerate = true)
val refByChildId: Long,
val refText: String
)
// POJOS
// The Child has exactly one ReferencedByChild reference. This POJO joins those two
class ChildWithReferenced(
#Embedded
var child: Child,
#Embedded
var referencedByChild: ReferencedByChild
)
class OwnerWithEverything {
#Embedded
var owner: Owner? = null
#Relation(
parentColumn = "ownerId",
entityColumn = "referencedOwnerId",
entity = Child::class // which entity should be defined here?
)
var childrenWithReferenced: List<ChildWithReferenced>? = null
}
Building this code results in this error message:
error: There is a problem with the query: [SQLITE_ERROR] SQL error or missing database (no such column: refByChildId)
I think that the Owner query is badly constructed, but I am not entirely sure. If that is the problem, what is the correct way to construct the query?
This is the original question
I have a nested POJO structure that should represent a single Game having multiple Rounds and each Round has a single Topic associated with it:
class GameWithRounds {
#Embedded
var game: Game? = null
#Relation(
parentColumn = "id",
entityColumn = "gameId",
entity = RoundRoom::class
)
var rounds: List<RoundWithTopic>? = null
}
class RoundWithTopic(
#Embedded
var round: RoundRoom,
#Embedded(prefix = "topic_")
var topic: Topic
)
The embedded annotation on Topic specifies a prefix because there are clashing id properties.
The Room Query that can fetch those classes is:
#Query("SELECT Topic.id as topic_id, Topic.name as topic_name, (...), RoundRoom.* FROM RoundRoom INNER JOIN Topic ON RoundRoom.topicId = Topic.id")
abstract fun findRoundsWithTopics(): List<RoundWithTopic>
However, building the project gives me Room errors:
There is a problem with the query: [SQLITE_ERROR] SQL error or missing database (no such column: topic_id)
Even though when I induce a warning about which fields are actually present, this is what Room tells me:
Columns returned by the query: topic_id, topic_name, topic_description, topic_language, topic_keywords, topic_sourceUrls, topic_furtherUrls, topic_questions, order, gameId, topicId, status, id. Fields in cz.melkamar.sklapecka.model.RoundWithTopic: order, gameId, topicId, status, id, topic_id, topic_name, topic_description, topic_language, topic_keywords, topic_sourceUrls, topic_furtherUrls, topic_questions, topic_image.
The topic_id column is there in the query result! Why am I getting this error?
For completeness, this is the entities:
#Entity
data class Game(
#PrimaryKey(autoGenerate = true)
val id: Long = 0,
#Embedded
val gameConfigurationEmbed: GameConfigurationEmbed
)
data class GameConfigurationEmbed(
var secondsPerTurn: Int,
var maxSecondsPerTurn: Int,
var bonusSecondsPerAnswer: Int
)
#Entity(
foreignKeys = [
ForeignKey(
entity = Game::class,
parentColumns = arrayOf("id"),
childColumns = arrayOf("gameId"),
onDelete = ForeignKey.CASCADE
),
ForeignKey(
entity = Topic::class,
parentColumns = arrayOf("id"),
childColumns = arrayOf("topicId"),
onDelete = ForeignKey.CASCADE
)
]
)
#TypeConverters(RoomConverters::class)
data class RoundRoom(
val order: Int,
var gameId: Long,
val topicId: String,
var status: RoundStatus = RoundStatus.CREATED,
#PrimaryKey(autoGenerate = true)
val id: Long = 0
) {
enum class RoundStatus {
CREATED, UPCOMING, IN_PROGRESS, FINISHED
}
}
#Entity
data class Topic(
#PrimaryKey val id: String,
val name: String,
val description: String,
val language: String,
val keywords: List<String>,
val sourceUrls: List<String>,
val furtherUrls: List<String>,
val questions: List<String>,
val image: ByteArray?
)
After some research, specifically looking at this link : How can I represent a many to many relation with Android Room?
the only answers we found would be to
either create a hand-made sql query to handle this type of situation
where you have a many-to-many relationship
OR
to alternatively have an additional joining entity which gets
updated as the rest of the objects are updated. With this approach, you can get the ID's and then create additional queries as needed
It seems embedded fields and type converter is not properly used on observing the question. I don't want to go in detail in the solution of the question since it is trying to use complex relations and I cannot test it replicating in my machine.
But I want to provide insight on using Embedded fields and TypeConverter.
Let's take an example from the question above:
Game table has fields
id, secondsPerTurn, maxSecondsPerTurn, bonusSecondsPerAnswer.
It is okay to create entity like below.
#Entity
data class Game(
#PrimaryKey(autoGenerate = true)
val id: Long = 0,
#Embedded
val gameConfigurationEmbed: GameConfigurationEmbed
)
data class GameConfigurationEmbed(
var secondsPerTurn: Int,
var maxSecondsPerTurn: Int,
var bonusSecondsPerAnswer: Int
)
Here in the SQLite table, data is actually stored in four different columns but Room does CRUD operation based on data class structure giving higher feasibilty to the developers.
TypeConverter
Type converter will be helpful if we want to store non primitive data types or same type of data which will not be covered by #Embedded.
For example, a football game can be held in two places: home and away. Home and Away can have the same field names like placeName, latitude, longitude. In this case, we can create data class and type converters like below:
data class GamePlace(
val placeName:String,
val latitude:String,
val longitude:String
)
#Entity
data class Game(
#PrimaryKey(autoGenerate = true)
val id: Long = 0,
#Embedded
val gameConfigurationEmbed: GameConfigurationEmbed
#TypeConverters
var home: GamePlace? = null,
#TypeConverters
var away: GamePlace? = null,
)
object Converters {
private val gson = Gson()
#TypeConverter
#JvmStatic
fun fromGamePlace(gamePlace: GamePlace?): String? {
return if (gamePlace == null) null else gson.toJson(gamePlace)
}
#TypeConverter
#JvmStatic
fun toGamePlace(jsonData: String?): GamePlace? {
return if (jsonData.isNullOrEmpty()) null
else gson.fromJson(jsonData, object : TypeToken<GamePlace?>() {}.type)
}
}
While using type converter, converter class should be defined in database class as below:
#Database(
entities = [Game::class /* ,more classes here*/],
version = 1
)
#TypeConverters(Converters::class)
abstract class AppDatabase : RoomDatabase() {
abstract fun gameDao(): GameDao
//.....
}
I hope this will help to deal with Embedded and TypeConverter in Room.