检查列 NULL 或 Room DB 中是否为空

Question

I want to get a list of MyModel whose deletedAt value is NULL . Here is my table:

@Entity(tableName = "my_table")
data class MyModel(
    @PrimaryKey
    @ColumnInfo(name = "id")
    var id: String,
    @ColumnInfo(name = "deletedAt")
    var deletedAt: Date? = null
)

Dao:

@Dao
abstract class MyDao : BaseDao<MyModel> {

@Query("SELECT * from my_table WHERE deletedAt IS NULL")
abstract fun getList(): LiveData<List<MyModel>>
}

My TypeConverter:

object DateTypeConverter {
@TypeConverter
@JvmStatic// It need to added else gives unwanted data binding error :D
fun fromTimestamp(value: Long?): Date? {
    return if (value == null) null else Date(value)
}

@TypeConverter
@JvmStatic
fun dateToTimestamp(date: Date?): Long? {
    return date?.time
}

But it returns all of MyModel data even if deletedAt values are null for some entries.

Answer 1

Try to use NULLIF to check null or empty like below

NULLIF(deletedAt, '') IS NULL

Complete Query is

@Query("SELECT * from my_table WHERE NULLIF(deletedAt, '') IS NULL")

Answer 2

You can use in model class

@ColumnInfo(name = "user_name")
@NonNull private String strname;

Answer 3

Just write

@Query("SELECT * from my_table WHERE deletedAt IS NULL")

a common mistake is writing like null
make sure that your data class is

data class(
    val id : Long,
    val deletedAt : Long? 
    /....
}