DAO Query to Swap Boolean Values in ROOM Database-CodePudding

I am working on a picture app where I have a list of pictures entities cached in a ROOM database:

This is my Picture Entity class:

@Entity
data class PictureEntity(

    @PrimaryKey
    val id: String,
    val title: String,
    val url: String,
    var isFavorite:Boolean)

I am looking to toggle the boolean value of isFavorite field when a user hits the Mark/Unmark favorite button in the UI for that particular picture item's isFavorite field

I am using this dao query but it is updating all the fields for isFavorite column.

@Update(onConflict = OnConflictStrategy.REPLACE)
suspend fun updatePicture(picture: PictureEntity)

What I want is to just update one single field for the picture which has been selected favorite.

I tried this query too but I got an error:

@Query("UPDATE picture_table SET isFavorite = NOT isFavorite")
suspend fun updatePicture()

I am totally lost and can't find any way around this issue. I will appreciate any help to get me back on track.

CodePudding user response：

To update an entity in room database you need the to use the same object with the change that you want so for example in you case you should make a copy from picture object where you toggle isFavorite like that:

val pictures = getAllPicturesFromRoom()
val picture = pictures[0]

updatePicture(picture.copy(isFavorite = !picture.isFavorite))

Also no need for OnConflictStrategy in update function so your update function should look like this:

@Update
suspend fun updatePicture(picture: PictureEntity)

CodePudding user response：

I am using this dao query but it is updating all the fields for isFavorite column.

That's how the convenience @Update works, it finds the appropriate row according to the primary key and updates all of the other columns.

I tried this query too but I got an error: @Query("UPDATE picture_table SET isFavorite = NOT isFavorite")

You have the wrong table name, it is, according to the provided code, pictureEntity. Furthermore, you have no clause limiting the update to a specific row, therefore it would toggle ALL rows in the table.

You should be using something like:-

@Query("UPDATE pictureEntity SET isFavorite = NOT isFavorite WHERE id=:id")

As an example consider the following snippet :-

    ....

    dao.insert(PictureEntity("Picture1","Picture1","TheURL",false))
    dao.insert(PictureEntity("Picture2","Picture2","TheURL",true))
    dao.insert(PictureEntity("Picture3","Picture3","TheURL",false))

    logPictures("STAGE1")
    dao.toggleFavorite("Picture2")
    logPictures("STAGE2")
}

fun logPictures(tagSuffix: String) {
    for(pe in dao.getAllPictures()) {
        Log.d("DBINFO_$tagSuffix","Picture is ${pe.id} Title is ${pe.title} isFavorite is ${pe.isFavorite}")
    }
}

The result being :-

D/DBINFO_STAGE1: Picture is Picture1 Title is Picture1 isFavorite is false
D/DBINFO_STAGE1: Picture is Picture2 Title is Picture2 isFavorite is true
D/DBINFO_STAGE1: Picture is Picture3 Title is Picture3 isFavorite is false


D/DBINFO_STAGE2: Picture is Picture1 Title is Picture1 isFavorite is false
D/DBINFO_STAGE2: Picture is Picture2 Title is Picture2 isFavorite is false
D/DBINFO_STAGE2: Picture is Picture3 Title is Picture3 isFavorite is false

i.e. Picture2 has been toggled from true to false, Picture1 and Pictuire3 remain as they were (false)