entityandroid-roomandroid-databaseandroid-room-embedded

Android Room Embedded Field Not Compiling

I am trying to create an embedded field. This is a simple example but I can't get this simple example to work. Eventually I need to have 3 levels of embedded items but trying to get this test case to work.

@Entity(tableName = "userItemsEntity")
@Parcelize
data class Item(
    var objecttype: String?,
    @PrimaryKey(autoGenerate = false)
    var objectid: Int?,
    var subtype: String?,
    var collid: Int?,
    @Embedded
    var name: Name?
) : Parcelable

@Parcelize
data class Name(
    var primary: Boolean? = true,
    var sortindex: Int? = null,
    var content: String? = null) : Parcelable

When I try and compile it it complains on the DAO that the updateItem()

SQL error or missing database (no such column: name)

DAO function

@Query("UPDATE userItemsEntity SET " +
    "objecttype=:objecttype, objectid=:objectid, subtype=:subtype, collid=:collid, name=:name " +
    "WHERE objectid=:objectid")
fun updateItem(
    objecttype: String?,
    objectid: Int,
    subtype: String?,
    collid: Int?,
    name: Name?)
Solution

  • The reason is as it says there is no name column. Rather the table consists of the columns, as per the member variables of the EMBEDDED class (i.e. primary, sortindex and content).

    i.e. the table create SQL is/will be :-

    CREATE TABLE IF NOT EXISTS `userItemsEntity` (`objecttype` TEXT, `objectid` INTEGER, `subtype` TEXT, `collid` INTEGER, `primary` INTEGER, `sortindex` INTEGER, `content` TEXT, PRIMARY KEY(`objectid`))

    Room knows to build the respective Name object from those columns when extracting rows.

    So you could use :-

    @Query("UPDATE userItemsEntity SET " +
        "objecttype=:objecttype, objectid=:objectid, subtype=:subtype, collid=:collid, `primary`=:primary, sortindex=:sortindex, content=:content " +
        "WHERE objectid=:objectid")
fun updateItem(
    objecttype: String?,
    objectid: Int,
    subtype: String?,
    collid: Int?,
    primary: Boolean?,
    sortindex: Int?,
    content: String?
)

    However, as you are using a WHERE clause based upon the primary key (objectid) then the update will only apply to a single row and as such you can simply use:-

    @Update
fun update(item: Item): Int

    Impementing a name column

    If you want a name column and for that name column to hold a Name object. Then, as SQLite does not have storage/column types for objects then you would not EMBED the Name class.

    You would have var name: Name? with an appropriate TypeConverter that would convert the Name object into a type that SQLite caters for :-

    However, using a JSON representation of an object, introduces bloat and reduces the usefulness of the converted data from an SQL aspect.

    For example say you had :-

    @Entity(tableName = "userOtherItemsEntity")
@Parcelize
data class OtherItem (
    var objecttype: String?,
    @PrimaryKey(autoGenerate = false)
    var objectid: Int?,
    var subtype: String?,
    var collid: Int?,
    var name: OtherName?) : Parcelable
@Parcelize
data class OtherName(
    var primary: Boolean? = true,
    var sortindex: Int? = null,
    var content: String? = null) : Parcelable

    Then the underlying table does have the name column. The CREATE SQL, generated by Room, would be :-

    CREATE TABLE IF NOT EXISTS `userOtherItemsEntity` (`objecttype` TEXT, `objectid` INTEGER, `subtype` TEXT, `collid` INTEGER, `name` TEXT, PRIMARY KEY(`objectid`))

    However, you would need TypeConverters which could be :-

    @TypeConverter
fun fromOtherName(othername: OtherName ): String {
    return Gson().toJson(othername)
}
@TypeConverter
fun toOtherName(json: String): OtherName {
    return Gson().fromJson(json,OtherName::class.java)
}

    using Item with Name embedded then data would be stored along the lines of :-

    enter image description here

    Whilst with the OtherItem with OtherName being converted then the data (similar data) would be along the lines of :-

    enter image description here