CODEWITHSUNDEEP
androidkotlinrx-java2android-room
Sourabh
Sourabh

Reputation: 8482

Room - SELECT query, get or default

In SQL Brite, there's a method mapToOneOrDefault. Is there a similar thing in Room?

Say for Model

@Entity(tableName = "users")
data class User(@PrimaryKey val name: String)

and Dao

@Dao
interface UserDao {
    @Query("SELECT FROM users where name = :name")
    fun getUserByName(name: String): Flowable<User>
}

Not the stream returns nothing for getUserByName("John") if there's no John in DataBase. Is there a way to get a default value, say User("")?

Upvotes: 2

Views: 2849

Answers (2)

Blackbelt
Blackbelt

Reputation: 157457

Not the stream returns nothing for getUserByName("John") if there's no John in DataBase. Is there a way to get a default value, say User("")

There is no default mechanism.

You could change from Flowable<User> to Flowable<List<User>>. In case of no user you will get an empty list back. You can use a map to check and return a default value or filter+switchIfEmpty.

Or you could change from Flowable to Single. With Single, in case of no rows, matching your query, onError will be triggered. You can then implement onErrorReturn or onErrorResumeNext to return a default value

Upvotes: 4

Ahmed Ashraf
Ahmed Ashraf

Reputation: 2835

You can use Maybe instead of the Flowable in this case.

Maybe: Conceptually, it is a union of Single and Completable providing the means to capture an emission pattern where there could be 0 or 1 item or an error signaled by some reactive source.

You can then use the operator defaultIfEmpty to map to a new object if the query didn't return a value.

Reference

Upvotes: 0

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