Compare the Room Database and fetch the respective Data - mvvm

Question

We have Birthdate and Phone Number as user data. We need to Compare Today's date with Birthdate and fetch the Phone number to send an SMS.
We tried to use Repo class and View Model class, but unable to fetch details.

Answer 1

If you store the birthdate in a format supported by SQLite
see https://www.sqlite.org/lang_datefunc.html
Then you can use the 'now' timevalue (i.e. the date/ datetime NOW (i.e. when the query is run)).
As an example consider the following based upon a table (#Entity annotated class when dealing with Room) with 2 columns dob and altdob
two different formats
dob stores the time as a Long (more efficient storage wise)
altdob stores the date as a string format YYYY-MM-DD
4 rows are inserted with varying dates (both columns storing the same date)
Then a SELECT query that extracts the age (roughly) 3 ways and outputs the ages (3 columns output).
DROP TABLE IF EXISTS example; /* just in case table still exists */
CREATE TABLE IF NOT EXISTS example (dob INTEGER, altdob TEXT); /* create the table (room will do this) */
/* Add some data */
INSERT INTO example VALUES
(strftime('%s','1957-01-08'),'1957-01-08'),
(strftime('%s','1967-02-08'),'1967-02-08'),
(strftime('%s','1977-03-08'),'1977-03-08'),
(strftime('%s','1987-04-08'),'1987-04-08')
;
SELECT * FROM example; /* result 1 - the data as it is stored in the table */
/* result 2 the age in years (approx) using some of the datetime functions based upon the run/execution date */
SELECT
(strftime('%s','now')-dob) / (365 /* days in a year (close) */ * 24 /* hours in a day*/ * 60 /* mins in hour */ * 60 /* secs in minute*/) AS age,
(strftime('%s',date('now')) - strftime('%s',date(altdob))) / (365 * 24 * 60 * 60) AS altage,
date('now') - date(altdob)
FROM example;
DROP TABLE IF EXISTS example; /* cleanup demo environment */
When executed then the results are:-
Result 1
note the first column is the number of seconds since or before (if negative) 00:00:00 on 1st Jan 1970.
The second is obvious
the dates are the same just stored in different formats (both supported by the SQLite datetime functions)
Result 2
note that really there are not 365 days in a year (due to leap years)
Doing the above in Room (not mvvm for brevity/convenience)
First the Database related components:-
#Entity
data class Example(
#PrimaryKey
val dob: Long,
val altdob: String
)
data class POJOToGet3Ages(
val age: Int,
val altage: Int,
#ColumnInfo(name = "otheraltage") /* change to expect the output column name to be otheraltage instead of actual field name */
val notTheSameAsOutputColumnName: Int
)
#Dao
interface TheDAO {
#Insert(onConflict = OnConflictStrategy.IGNORE)
fun insert(example: Example): Long
#Query("SELECT " +
"(strftime('%s','now')-dob) / (365 /* days in a year (close) */ * 24 /* hours in a day*/ * 60 /* mins in hour */ * 60 /* secs in minute*/) AS age," +
"(strftime('%s',date('now')) - strftime('%s',date(altdob))) / (365 * 24 * 60 * 60) AS altage," +
"date('now') - date(altdob) AS otheraltage " +
"FROM example;")
fun getAllAges(): List<POJOToGet3Ages>
}
#Database(entities = [Example::class], exportSchema = false, version = 1)
abstract class TheDatabase: RoomDatabase() {
abstract fun getTheDAO(): TheDAO
companion object {
private var instance: TheDatabase?=null
fun getInstance(context: Context): TheDatabase {
if (instance==null) {
instance = Room.databaseBuilder(context,TheDatabase::class.java,"the_database.db")
.allowMainThreadQueries() /* run on main thread for brevity/convenience */
.build()
}
return instance as TheDatabase
}
}
}
To utilise the above some activity code (MainActivity) that will replicate the demo above (add the same 4 rows) and extract the ages based upon the date now and output the results to the log :-
class MainActivity : AppCompatActivity() {
lateinit var dbInstance: TheDatabase
lateinit var dao: TheDAO
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
dbInstance = TheDatabase.getInstance(this)
dao = dbInstance.getTheDAO()
dao.insert(Example(-409622400,"1957-01-08"))
dao.insert(Example(-91411200,"1967-02-08"))
dao.insert(Example(226627200,"1977-03-08"))
dao.insert(Example(544838400,"1987-04-08"))
for (ages in dao.getAllAges()) {
Log.d("DBINFO","Ages is ${ages.age} ALTAGE is ${ages.altage} OTHERALTAGE is ${ages.notTheSameAsOutputColumnName}")
}
}
}
When run the log includes:-
D/DBINFO: Ages is 66 ALTAGE is 66 OTHERALTAGE is 66
D/DBINFO: Ages is 55 ALTAGE is 55 OTHERALTAGE is 56
D/DBINFO: Ages is 45 ALTAGE is 45 OTHERALTAGE is 46
D/DBINFO: Ages is 35 ALTAGE is 35 OTHERALTAGE is 36