Develop Reference

Android Room doesn't allow me to do the one-to-N relationship multiple times

I have implemented a DB where I have two one-to-many relationships but it would seem that room does not allow it. Is that so?
The entities are:
#Entity(tableName = "arete_sheet")
data class EAreteSheet(
#PrimaryKey val id: Long,
#ColumnInfo(name = "sheet") val form: Sheets,
#ColumnInfo(name = "version") val version: Int,
)
#Entity(tableName = "arete_sheet_paragraph")
data class EAreteSheetParagraph(
#PrimaryKey val id: Long,
#ColumnInfo(name = "arete_sheet_id") val sheet: Long,
#ColumnInfo(name = "name") val name: String
)
#Entity(tableName = "arete_sheet_form")
data class EAreteSheetForm(
#PrimaryKey val id: Long,
#ColumnInfo(name = "arete_sheet_paragraph_id") val paragraph: Long,
#ColumnInfo(name = "fieldType") val fieldType: FieldType,
#ColumnInfo(name = "cell") val cell: String,
#ColumnInfo(name = "label") val label: String
)
To solve the schema I have implemented these join classes:
data class EAreteSheetWithParagraph(
#Embedded val sheet: EAreteSheet,
#Relation(
parentColumn = "id",
entityColumn = "arete_sheet_id"
)
val paragraph: List<EAreteSheetParagraphWithForm>
)
data class EAreteSheetParagraphWithForm(
#Embedded val paragraph: EAreteSheetParagraph,
#Relation(
parentColumn = "id",
entityColumn = "arete_sheet_paragraph_id"
)
val forms: List<EAreteSheetForm>
)
This is the DAO implementation:
#Transaction
#Query("SELECT * FROM arete_sheet")
suspend fun getSheetWithParagraphsAndForms(): List<EAreteSheetWithParagraph>
This is the mistake he gives me in the building phase:
app/build/generated/source/kapt/debug/it/ximplia/agri2000/model/db/dao/AreteSheetDAO_Impl.java:203: error: constructor EAreteSheetWithParagraph in class EAreteSheetWithParagraph cannot be applied to given types;
_item = new EAreteSheetWithParagraph();
^
required: EAreteSheet,List<EAreteSheetParagraphWithForm>
found: no arguments
reason: actual and formal argument lists differ in length
app/build/generated/source/kapt/debug/it/ximplia/agri2000/model/db/dao/AreteSheetDAO_Impl.java:204: error: sheet has private access in EAreteSheetWithParagraph
_item.sheet = _tmpSheet;
I think that Room does not allow to resolve dependencies in cascade but I would like to know if someone was successful or if I made a mistake before changing the code.

In EAreteSheetWithParagraph you are specifying a list of EAreteSheetParagraphWithForm's
as per :-
val paragraph: List<EAreteSheetParagraphWithForm>
The #Relation will try to ascertain the columns as per the EAreteSheetParagraphWithForm form class, which is not an Entity. You should change the #Relation to specify the appropriate entity (i.e. the EAreteSheetParagraph) using the entity parameter.
So EAreteSheetWithParagraph should be something like :-
data class EAreteSheetWithParagraph(
#Embedded val sheet: EAreteSheet,
#Relation(
entity = EAreteSheetParagraph::class,
parentColumn = "id",
entityColumn = "arete_sheet_id"
)
val paragraph: List<EAreteSheetParagraphWithForm>
)
However, I don't believe that you are getting that far, as the messages appear to be complaining about the sheet variable which has a type of Sheets (and that the variable is private).
Without adding the entity= parameter then the compile, if it reached that stage, would fail with :-
> Task :app:kaptDebugKotlin FAILED
error: The class must be either #Entity or #DatabaseView. - a.a.so68953488kotlinroommany1_n.EAreteSheetParagraphWithForm
E:\AndroidStudioApps\SO68953488KotlinRoomMany1N\app\build\tmp\kapt3\stubs\debug\a\a\so68953488kotlinroommany1_n\EAreteSheetWithParagraph.java:12: error: Cannot find the child entity column `arete_sheet_id` in a.a.so68953488kotlinroommany1_n.EAreteSheetParagraphWithForm. Options:
private final java.util.List<a.a.so68953488kotlinroommany1_n.EAreteSheetParagraphWithForm> paragraph = null;
^
The class must be either #Entity or #DatabaseView. - a.a.so68953488kotlinroommany1_n.EAreteSheetParagraphWithForm
I think that Room does not allow to resolve dependencies in cascade but I would like to know if someone was successful or if I made a mistake before changing the code.
As indicated above, I believe the issue is mistakes so :-
Proof of concept
Based upon your code the following shows that nested/multiple 1-n's do work:-
Using your code BUT with the following changes (to avoid issues and simplify) :-
#Entity(tableName = "arete_sheet_form")
data class EAreteSheetForm(
#PrimaryKey val id: Long,
#ColumnInfo(name = "arete_sheet_paragraph_id") val paragraph: Long,
#ColumnInfo(name = "fieldType") val fieldType: /* FieldType */ String, // changed for convenience/brevity
#ColumnInfo(name = "cell") val cell: String,
#ColumnInfo(name = "label") val label: String
)
fieldType' stype changed from FieldType to String so no need for extra class and type converters.
and
#Entity(tableName = "arete_sheet")
data class EAreteSheet(
#PrimaryKey val id: Long,
#ColumnInfo(name = "sheet") val form: /*Sheets*/ String, // changed for convenience/brevity
#ColumnInfo(name = "version") val version: Int,
)
Sheets type substituted with String
EAreteSheetWithParagraph as above
EAreteSheetParagraphWithForm changed to
data class EAreteSheetParagraphWithForm(
#Embedded val paragraph: EAreteSheetParagraph,
#Relation(
parentColumn = "id",
entityColumn = "arete_sheet_paragraph_id",
entity = EAreteSheetForm::class
)
val forms: List<EAreteSheetForm>
)
i.e. the entity parameter has been added according to my preference to always code the entity parameter.
AreteSheetDao used :-
#Dao
abstract class AreteSheetDAO {
#Insert
abstract fun insert(eAreteSheet: EAreteSheet): Long
#Insert
abstract fun insert(eAreteSheetParagraph: EAreteSheetParagraph): Long
#Insert
abstract fun insert(eAreteSheetForm: EAreteSheetForm): Long
#Transaction
#Query("SELECT * FROM arete_sheet")
abstract fun getSheetWithParagraphsAndForms(): List<EAreteSheetWithParagraph>
}
Code in an Activity :-
class MainActivity : AppCompatActivity() {
lateinit var db: TheDatabase
lateinit var dao: AreteSheetDAO
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
db = TheDatabase.getInstance(this)
dao = db.getDao()
var s1 = dao.insert(EAreteSheet(10,"Sheet1",1))
var s2 = dao.insert(EAreteSheet(20,"Sheet2",1))
var p1 = dao.insert(EAreteSheetParagraph(100,s1,"Para1 (Sheet1)"))
var p2 = dao.insert(EAreteSheetParagraph(101,s1,"Para2 (Sheet1)"))
var p3 = dao.insert(EAreteSheetParagraph(201,s2,"Para3 (Sheet2)"))
var p4 = dao.insert(EAreteSheetParagraph(202,s2,"Para4 (Sheet2)"))
var f1 = dao.insert(EAreteSheetForm(1000,p1,"typex","cellx","Form1"))
var f2 = dao.insert(EAreteSheetForm(1001,p1,"typex","cellx","Form2"))
var f3 = dao.insert(EAreteSheetForm(1002,p1,"typex","cellx","Form3"))
var f4 = dao.insert(EAreteSheetForm(1010,p2,"typex","cellx","Form4"))
var f5 = dao.insert(EAreteSheetForm(1011,p2,"typex","cellx","Form5"))
var f6 = dao.insert(EAreteSheetForm(1020,p3,"typex","cellx","Form6"))
val TAG = "ARETEINFO"
for(sw: EAreteSheetWithParagraph in dao.getSheetWithParagraphsAndForms()) {
Log.d(TAG,"Sheet ID is ${sw.sheet.id} Form is ${sw.sheet.form} Version is ${sw.sheet.version}" )
for(pf: EAreteSheetParagraphWithForm in sw.paragraph) {
Log.d(TAG,"\tPara is ${pf.paragraph.name} etc")
for(f: EAreteSheetForm in pf.forms) {
Log.d(TAG,"\t\tForm is ${f.label}")
}
}
}
}
}
As can be seen, some data is loaded, 2 Sheets, each with 2 paragraphs and then 4 forms distributed unevenly (3 to para1, 2 to para2, 1 to para3, 0 to para4).
The data is then extracted (as array of EAreteSheetWithParagraph), the array traversed (traversing the underlying arrays of paragraphs and forms within paragraphs) and output to the log the Result being :-
D/ARETEINFO: Sheet ID is 10 Form is Sheet1 Version is 1
D/ARETEINFO: Para is Para1 (Sheet1) etc
D/ARETEINFO: Form is Form1
D/ARETEINFO: Form is Form2
D/ARETEINFO: Form is Form3
D/ARETEINFO: Para is Para2 (Sheet1) etc
D/ARETEINFO: Form is Form4
D/ARETEINFO: Form is Form5
D/ARETEINFO: Sheet ID is 20 Form is Sheet2 Version is 1
D/ARETEINFO: Para is Para3 (Sheet2) etc
D/ARETEINFO: Form is Form6
D/ARETEINFO: Para is Para4 (Sheet2) etc

Android Room Observer: Relational data update not displayed correctly

I am having a relational data structure like the following
Entry.kt
#Entity(tableName = "entries")
data class Entry(
#ColumnInfo(name = "entry_id") #PrimaryKey(autoGenerate = true) val entryID: Long,
#ColumnInfo(name = "time_stamp") val timeStamp: Timestamp
)
Feeling.kt
#Entity(tableName = "feelings")
data class Feeling(
#ColumnInfo(name = "feeling_id") #PrimaryKey(autoGenerate = true) val feelingID: Int,
val feeling: String,
val color: Int
)
Subentry.kt
#Entity(tableName = "sub_entries",indices = [Index("feeling_id")])
data class SubEntry(
#ColumnInfo(name = "sub_entry_id") #PrimaryKey(autoGenerate = true) val subEntryID: Long,
#ColumnInfo(name = "entry_id") var entryID: Long,
#ColumnInfo(name = "feeling_id") val feelingID: Int,
val intensity: Int
)
as well as a DOJO linking the three
EntryWithSubEntriesAndFeelings.kt
data class EntryWithSubEntriesAndFeelings(
#Embedded val entry: Entry,
#Relation(
parentColumn = "entry_id",
entityColumn = "entry_id"
)
val subEntries: List<SubEntry>,
#Relation(
parentColumn = "entry_id",
entityColumn = "feeling_id",
associateBy = Junction(SubEntry::class)
)
val feelings: List<Feeling>
)
Now with a prepopulated feelings database, everything works fine. But I am currently adding the feature to insert custom feelings. Those and the corresponding subentries end up correctly in the subentry database (I copied the database files from the virtual device and checked them manually). But for some reason, the new feeling is not getting passed to the observer and the adapter and thus it is not being displayed together with the other subentries.
Any hints are appreciated! :)

Turns out I still had some hardcoded references to the initial list in my code which prevented the new feeling from being displayed.

How to autogenerate a Room database id without providing an id

I am trying to create a room database and I want each item inserted into it to have its own unique id without me having to provide it, The problem is when I try to insert new items into the database I get an error asking me to provide an id.
Here is my entity:
#Entity(tableName = "notes_table")
data class Note(
#PrimaryKey(autoGenerate = true)
val id: Int = 0,
#ColumnInfo(name = "description")
val description: String,
#ColumnInfo(name = "priority")
var priority: Int)
Is there a way to have the database create its own auto-generated auto-increasing id column without having me having to add it like this:
val item = Note(id, item, priority)
insert(item)
And instead do this:
val item = Note(item, priority)
insert(item)

Create a constructor that takes item and priority as arguments
#Entity(tableName = "notes_table")
data class Note (var item: String,
#ColumnInfo(name = "priority")
var priority: String) {
#PrimaryKey(autoGenerate = true)
var id: Long = 0,
//.....
}

You can just simply give the id a default value and put that at the end:
#Entity(tableName = "notes_table")
data class Note(
#ColumnInfo(name = "description")
val description: String,
#ColumnInfo(name = "priority")
var priority: Int)
#PrimaryKey(autoGenerate = true) //must be at the end
val id: Int = 0 //Long type recommend
)
Then you can:
val item = Note(item, priority)
insert(item)

Because your data class Note has three parameter.
So you you have to create Note by passing three parameter.
It is nothing to do with autogenerate or room.

Why do I have to make a setter for an auto-incremented column in a database?

In my android app I have created a database using the room persistance library. It contains of a table called stack with the columns stack_id, col_1, col_2 and stack_name. Here's the code for the entity class:
#Entity
class Stack(
#ColumnInfo(name = "stack_name") val stackName: String,
#ColumnInfo(name = "col_1") val column1: String,
#ColumnInfo(name = "col_2") val column2: String
) {
#PrimaryKey(autoGenerate = true) #ColumnInfo(name = "stack_id") val
stackId: Int = 0
}
Question 1: Is the stack_id correctly implemented? I found this solution to set en auto-incremented column to 0 and it will automaticly auto-increment the value, but it doesn't make sense to me. So, is this correct?
Question 2: Whe I want to build the app, it throws the error:
Cannot find setter for field. private final int stackId = 0;
But it would be nonsense to make a setter for an auto-incremented value. So, should I make a setter or is there another solution?

You are using concrete class so you need to provide get() and set() for properties.
Use data class which are build for this purpose only .
#Entity
data class Stack(
#PrimaryKey(autoGenerate = true) #ColumnInfo(name = "stack_id") val id: Int? = null,
#ColumnInfo(name = "stack_name") val stackName: String,
#ColumnInfo(name = "col_1") val column1: String,
#ColumnInfo(name = "col_2") val column2: String)

You need to move
#PrimaryKey(autoGenerate = true) #ColumnInfo(name = "stack_id") val
stackId: Int = 0
to the constructor.
#Entity
class Stack(
#PrimaryKey(autoGenerate = true) #ColumnInfo(name = "stack_id") val
stackId: Int = 0,
#ColumnInfo(name = "stack_name") val stackName: String,
#ColumnInfo(name = "col_1") val column1: String,
#ColumnInfo(name = "col_2") val column2: String
)
Why this works? The property is val, so is final/immutable, but the assignment in the constructor is a default value which can be overridden by passing in a value.
However in your example the property is in the class body and is assigned the value 0 on init, and cannot be changed as property is immutable.
The second option, as pointed out, is making the property mutable by using var instead of val.

Check if an entry is already in a livedata list wihout looping through the list

I am trying to build an app to help me track some of the tasks we have to do in the game.
I have a Firebase Firestore database that store all the tasks and I download at the application launch the data and add only the one I don't have.
Here is my entry model:
#Entity(tableName = "entry_table")
data class Entry(
#PrimaryKey(autoGenerate = true) var uid: Long?,
#ColumnInfo(name = "title") val title: String,
#ColumnInfo(name = "description") val description: String,
#ColumnInfo(name = "target") val target: Int = 0,
#ColumnInfo(name = "position") val position: Int = 0,
#ColumnInfo(name = "starred") val starred: Boolean = false
) {
constructor(): this(null, "", "", 0, 0, starred = false)
}
Since I download the document from the firestore database I cannot set an ID before inserting the entries in my SQLite database.
This means that I cannot use the "contains" method on my livedata list (since the entries I recieve has a "null" id and the one from the database has an id). I need to loop though all the data, here is the code:
#WorkerThread
suspend fun insertEntry(entry: Entry) {
for (doc in entriesList.value!!){
if (doc.description == entry.description && doc.title == entry.title) {
Log.d("MAIN_AC", "Entry already saved $entry")
return
}
}
entryDAO.insertEntry(entry)
}
My code works but I am not satisfied with it, is there a better way to make this happen? I was hoping that the contains method could ignore some arguments (in my case the autogenerated ID)

One way you can go about, assuming you are using Room, it is to annotate your insert function (in the relevant DAO) with OnConflictStrategy.IGNORE.
e.g.
#Dao
interface EntryDao {
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(list: List<Entry>)
// or (if you want the inserted IDs)
// fun insert(list: List<Entry>) : LongArray
}
Be sure to also annotate your entity with the relevant unique index.
e.g.
#Entity(tableName = "entry_table",
indices = [Index(value = ["title", "description"], unique = true)]
)
data class Entry(
#PrimaryKey(autoGenerate = true) var uid: Long,
#ColumnInfo(name = "title") val title: String,
#ColumnInfo(name = "description") val description: String
//...
)
Primary keys should not be null-able, you can .map to Entry wit uid = 0. If you are using the same entity model both locally and remotely that is probably not the best idea.