Search query using Android room relation - android

In Android room relation, is it possible to use search query using the property of the related table. Below is my table structure. In this i am relating transaction with payment and lines(transaction items). I have an search field in my UI where the user could search using payment amount which is inside payment table. How to form a query to access the properties of payment table.
class TransactionWithPaymentAndLines(
#Embedded
var transactions: Transactions? = null,
#Relation(
parentColumn = "id",
entityColumn = "transactionId",
entity = Payment::class
)
var payments: List<Payment> = listOf(),
#Relation(
parentColumn = "id",
entityColumn = "transactionId",
entity = TransactionLines::class
)
var transactionLines: List<TransactionLines> = listOf()
)


Ideal way is to query multiple related tables is to create a View. A view combines data from two or more tables using join.
In Android, using Room Persistance library, you can create such a view, and then you can query the fields of view. This is how you can do it:
Suppose, you have tables:
User: id, name, departmentId
Department: id, name
Create a View:
#DatabaseView("SELECT user.id, user.name, user.departmentId," +
"department.name AS departmentName FROM user " +
"INNER JOIN department ON user.departmentId = department.id")
data class UserDetail(
val id: Long,
val name: String?,
val departmentId: Long,
val departmentName: String?
)
Add View to Database:
#Database(entities = arrayOf(User::class),
views = arrayOf(UserDetail::class), version = 1)
abstract class AppDatabase : RoomDatabase() {
abstract fun userDetailDao(): UserDetailDao
}
Create a DAO:
#Dao
interface UserDetailDao {
#Query("SELECT * FROM UserDetail")
fun loadAllUserDetails(): Array<UserDetail>
}
Now, you can query a View using this DAO.


Absolutely possible, you can use #Query in your DAO class please read Room Database Documentation
Examples of #Query
#Query("SELECT * FROM user")
List<User> getAll();
#Query("SELECT * FROM user WHERE uid IN (:userIds)")
List<User> loadAllByIds(int[] userIds);
#Query("SELECT * FROM user WHERE first_name LIKE :first AND " +
"last_name LIKE :last LIMIT 1")
User findByName(String first, String last);


use #DB or #Query.
That should perfectly work...
#Query("SELECT * FROM TABLE_NAME")
List<Identifier> getAll();

Related

Room query returns list instead of map

I have a table Messages (PrimaryKey messageId) and a table ReadUpdates. Each message has many ReadUpdates that are related with
I want to query the Room Database with the below sql, and get a Map with key=Message and value=List
#Query(
"""
Select * from messages
inner join readUpdates on messages.messages_message_id = readUpdates.read_upd_message_id
where messages.messages_message_id = :messageId
and messages.messages_server_id = :serverId
"""
)
fun getMessageRecipients(
serverId: Long,
messageId: String
): LiveData<Map<Message, List<ReadUpdateAccount>>>
ReadUpdateAcccount is the model joined ReadUpdate and Account
data class ReadUpdateAccount(
#Embedded
val readUpdate: ReadUpdate,
#Relation(entity = Account::class, parentColumn = "read_upd_connection_id", entityColumn = "accounts_account_id")
val account: Account?
)
After debugging the query i see that instead of example
<Message(AAA), [ReadUpdateAccount(111), ReadUpdateAccount(222), ReadUpdateAccount(333)]>
i have
<Message(AAA), [ReadUpdateAccount(111)]> <Message(AAA), [ReadUpdateAccount(222)]>, <Message(AAA), [ReadUpdateAccount(333)]>
Obviously, i need the First but i get the Second
Why is this happening and how can i solve this?

how to populate intermediate table in Android

I have two tables with a many-to-many relationship. So I created an intermediate table, but I can't find a way to populate this table correctly because I can't set a correct list from my data.
I have a list of 'courses' : each 'course' can have one or several categories.
So my table looks like this :
|idcourses|title|date|categories|
|----|----|----|----|
|700|title1|01012021|[54]|
|701|title2|01022021|[54]|
|702|title3|01032021|[48]|
|868|title4|01042021|[47, 52, 54]|
If I try a map like this :
val myMap = coursesList.map { itcategory to it.idcourses}.distinct()
I have this kind of result :
([54], 700), ([54], 701), ([48], 702), ([47, 52, 54], 868)
The whole "[47, 52, 54]" is considered as one string but I want it to be split so I can have this :
([54], 700), ([54], 701), ([48], 702), ([47], 868), ([52], 868), ([54], 868)
Does anyone know how to achieve this ??

I believe that you may be trying to do this the wrong way as it appears that your intermediate table has a column where you are expecting a list of category id's.
You cannot have a column that is a list/array it has to be a single object.
However rather than try to fix that, what would typically be used for an intermediate table is a table that primarily has a single row per mapping. That is two columns that make up a mapping. Where the two columns are a composite primary key.
other columns that have data specific to the mapping can be used.
In your case one column to map/reference/relate/associate to the course and an second column to map the course.
For example, say you have the Course Table and the Category Table per:-
#Entity
data class Course(
#PrimaryKey
val idcourses: Long? = null,
val title: String,
val date: String
)
and
#Entity
data class Category(
#PrimaryKey
val idcategories: Long? = null,
val name: String
)
Then you could have the intermediate table as :-
#Entity(primaryKeys = ["idcoursesmap","idcategoriesmap"])
data class CourseCategoryMap(
val idcoursesmap: Long,
#ColumnInfo(index = true)
val idcategoriesmap: Long
)
the index on the idcategoriesmap will likely improve the efficiency. Room would also issue a warning.
you may wish to consider defining Foreign Key constraints to enforce referential integrity. None have been included for brevity.
This is sufficient for a many-many relationship.
You would probably want to retrieve Courses with the Categories so you would probably want a POJO for this such as:-
data class CourseWithCategories(
#Embedded
val course: Course,
#Relation(
entity = Category::class,
parentColumn = "idcourses",
entityColumn = "idcategories",
associateBy = Junction(
value = CourseCategoryMap::class,
parentColumn = "idcoursesmap",
entityColumn = "idcategoriesmap"
)
)
val categories: List<Category>
)
Here's some Dao's that would or may be wanted/useful:-
abstract class AllDao {
#Insert(onConflict = IGNORE) // Insert single Category
abstract fun insert(category: Category): Long
#Insert(onConflict = IGNORE) // Insert Single Course
abstract fun insert(course: Course): Long
#Insert(onConflict = IGNORE) // Insert Single CourseCategoryMap
abstract fun insert(courseCategoryMap: CourseCategoryMap): Long
/* Inserts many course category maps */
#Insert(onConflict = IGNORE)
abstract fun insert(courseCategoryMaps: List<CourseCategoryMap>): List<Long>
#Query("SELECT * FROM course WHERE course.title=:courseTitle")
abstract fun getCourseByTitle(courseTitle: String): Course
#Query("SELECT * FROM category WHERE category.name LIKE :categoryMask")
abstract fun getCategoriesByNameMask(categoryMask: String): List<Category>
/* For retrieving courses with all the courses categories */
#Transaction
#Query("SELECT * FROM course")
abstract fun getAllCoursesWithCategories(): List<CourseWithCategories>
#Transaction
#Query("")
fun insertManyCataegoriesForACourseByIds(idcourse: Long,categories: List<Long>) {
for (categoryId: Long in categories) {
insert(CourseCategoryMap(idcourse,categoryId))
}
}
// Anoher possibility
#Transaction
#Query("")
fun insertManyCategoriesForACourse(course: Course, categories: List<Category>) {
val categoryIds = ArrayList<Long>()
for (c: Category in categories) {
categoryIds.add(c.idcategories!!)
}
insertManyCataegoriesForACourseByIds(course.idcourses!!,categoryIds)
}
}
Demonstration
To demonstrate the above, a pretty standard class annotated with #Database :-
const val DATABASE_NAME = "the_database.db"
const val DATABASE_VERSION =1
#Database(entities = [Course::class,Category::class,CourseCategoryMap::class], exportSchema = false, version = DATABASE_VERSION)
abstract class TheDatabase: RoomDatabase() {
abstract fun getAllDao(): AllDao
companion object {
#Volatile
private var instance: TheDatabase? = null
fun getInstance(context: Context): TheDatabase {
if (instance == null) {
instance = Room.databaseBuilder(context,TheDatabase::class.java, DATABASE_NAME)
.allowMainThreadQueries()
.build()
}
return instance as TheDatabase
}
}
}
And activity code to replicate what it looks like your are attempting (but twice to show 2 ways of mapping, the second using category id's that are 20 greater then the first) :-
lateinit var db: TheDatabase
lateinit var dao: AllDao
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
db = TheDatabase.getInstance(this)
dao = db.getAllDao()
dao.insert(Course(idcourses = 700,title = "title1", date = "01012021"))
dao.insert(Course(701,"title2","01022021"))
dao.insert(Course(702,"title3","01032021"))
dao.insert(Course(868,"title4","01042021"))
// add quite a few categories for demo
for(i in 30..300) {
dao.insert(Category(i.toLong(),"Category${i}"))
}
//example of what you are trying to do (first)
var currentCourse = dao.getCourseByTitle("title1")
dao.insertManyCataegoriesForACourseByIds(currentCourse.idcourses!!, listOf(54))
dao.insertManyCataegoriesForACourseByIds(dao.getCourseByTitle("title2").idcourses!!, listOf(54))
dao.insertManyCataegoriesForACourseByIds(dao.getCourseByTitle("title3").idcourses!!, listOf(48))
dao.insertManyCataegoriesForACourseByIds(dao.getCourseByTitle("title4").idcourses!!, listOf(47,52,54))
// second (does the same but uses categroyids 20 greater than the first)
val coursecategorymaplist = listOf<CourseCategoryMap>(
CourseCategoryMap(700,74),
CourseCategoryMap(701,74),
CourseCategoryMap(702,68),
CourseCategoryMap(868,67),
CourseCategoryMap(868,72),
CourseCategoryMap(868,74)
)
dao.insert(coursecategorymaplist)
// Extract results
for (cwc: CourseWithCategories in dao.getAllCoursesWithCategories()) {
Log.d("DBINFO","Course is ${cwc.course.title}, date is ${cwc.course.date} it has ${cwc.categories.size} categories they are:-")
for (c: Category in cwc.categories) {
Log.d("DBINFO","\tCategory is ${c.name}")
}
}
}
Results
The log includes (note double the number of categories):-
D/DBINFO: Course is title1, date is 01012021 it has 2 categories they are:-
D/DBINFO: Category is Category54
D/DBINFO: Category is Category74
D/DBINFO: Course is title2, date is 01022021 it has 2 categories they are:-
D/DBINFO: Category is Category54
D/DBINFO: Category is Category74
D/DBINFO: Course is title3, date is 01032021 it has 2 categories they are:-
D/DBINFO: Category is Category48
D/DBINFO: Category is Category68
D/DBINFO: Course is title4, date is 01042021 it has 6 categories they are:-
D/DBINFO: Category is Category47
D/DBINFO: Category is Category52
D/DBINFO: Category is Category54
D/DBINFO: Category is Category67
D/DBINFO: Category is Category72
D/DBINFO: Category is Category74
The Database
The Course Table :-
The Category Table (partial)
The CourseCategoryMap (intermediate table)

Room automatically sorts on the basis of primary key in Android

I have a data class like this
#Entity
data class Question(
#field:SerializedName("question")
var question: String? = null,
#field:SerializedName("answers")
var answers: ArrayList<String?>? = null,
#field:SerializedName("id")
#PrimaryKey
var id: Int? = null
)
Then in DAO I have saving and getting methods like this
#Dao
interface QnADao {
#Insert(onConflict = OnConflictStrategy.REPLACE)
fun saveQuestion(questions:Question)
#Insert(onConflict = OnConflictStrategy.REPLACE)
fun saveAllQuestions(questions: List<Question?>?)
#Query("SELECT * from Question")
fun getAllQnA():List<Question>
}
I am saving a list of Questions and then later on retrieving them. So whenever I retrieve them I get the list sorted according to the id which is the primary key.
So if I am saving questions with id:254, id:23, id:45 and id:92 then I am getting it like this id:23, id:45, id:92 and id:254
But I don't need a sorted list like that, I need to get the data as it was saved in the database. Any help would be appreciated. Thanks.

Try to use autoGenerate = true for primary key so it will create PK number in sequence
See below lines
#PrimaryKey(autoGenerate = true)
So that now your insert and retrive order will be same

You can add a Date field to your Question entity
#field:SerializedName("date")
var date: Date? = null,
and order your entities by date
#Query("SELECT * FROM Question ORDER BY date DESC")

Android Room Allow Dao #Query to populate #Ignore columns

I'm wanting my Dao to populate #Ignore columns in my Entity class. For example:
Entity
#Entity(tableName = "example")
data class Example(
#PrimaryKey
val id: Long,
val value: Int
) {
#Ignore
var nextId: Long = 0L
}
Dao
#Dao
interface ExampleDao {
#Query(value = "SELECT *, (id + 1) AS nextId FROM example")
fun getAllExamples(): List<Example>
}
However, when the application gets built, the following warning gets produced:
The query returns some columns [nextId] which are not used by com.example.app.Example and it doesn't populate nextId.
Is it possible to include #Ignore columns in a #Query (if so, how)? If not, what are some strategies that can be employed to populate columns that are not present in my tables into my Entity class.
Note: I'm fully aware with the example provided that I can simply do something like:
#Ignore
val nextId: Long = id + 1
But is not the point of the question I am asking.

Based on the information that #CommonsWare has given me, the solution that I went with is
data class ExampleWithNextId(
#Embedded
val example: Example) {
var nextId: Long = 0L
}
Then use it in Dao like so
#Dao
interface ExampleDao {
#Query(value = "SELECT *, (id + 1) AS nextId FROM example")
fun getAllExamplesWithNextId(): List<ExampleWithNextId>
}

Android Room apply constraint to Relation

I'm aware Room lets us establish 1-N relations with the #Relation keyword. Although I'd like to know if it's possible to apply conditions to this relationship.
Let's say that I have the following POJO
class UserAndPets {
#Embedded
lateinit var user: User
#Relation(entityColumn = "ownerId", parentColumn = "userId")
lateinit var pets: List<Pets>
}
interface UserDao {
#Query("SELECT * FROM users WHERE userId = :userId LIMIT 1")
fun getUserAndPetsForUserId(userId: String): UserAndPets?
}
The above method lets me query a User and all his pets. Although is there a way for me to query the User and his last 10 pets for example? Or a User and all his Pets that would be a certain type?
Thanks

If the Id field in Pets is auto-incremented then this query should give you the result you are looking for:
#Query("SELECT * FROM pets WHERE ownerId = :userId ORDER BY Id DESC LIMIT 10")
By the way, the "LIMIT 1" in your Users query is unneccessary, the query would always return a single user.

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