Is it possible in Room to ignore a field on a basic update

Question

I have the following entity:

@Entity
class Foo(
    @PrimaryKey
    @ColumnInfo(name = "id")
    val id: Long,

    @ColumnInfo(name = "thing1")
    val thing1: String,

    @ColumnInfo(name = "thing2")
    val thing2: String,

    @ColumnInfo(name = "thing3")
    val thing3: String,

    @ColumnInfo(name = "thing4")
    val thing4: String
) {

    @ColumnInfo(name = "local")
    var local: String? = null

}

Where local is information that is not stored on the server, only local to the phone.

Currently when I pull information from the server GSON auto fills in my values, but since "local" does not come from the server it is not populate in that object.

Is there a way that when I call update I can have Room skip the update for the "local" column without writing a custom update to insert into all other columns except "local"? The pain point is that I could have many columns and each new column I add, I would have to add that to the custom insert statement.

I have also thought of a one-to-one mapping from the server entity to a new "local" entity, however now I have to deal with the pain of a join statement everywhere I get my entity since I need the local information.

I was hoping that I could do something like this:

@Entity
class Foo(
    @PrimaryKey
    @ColumnInfo(name = "id")
    val id: Long,

    @ColumnInfo(name = "thing1")
    val instructions: String,

    @ColumnInfo(name = "thing2")
    val instructions: String,

    @ColumnInfo(name = "thing3")
    val instructions: String,

    @ColumnInfo(name = "thing4")
    val instructions: String
) {

    @Ignore
    var local: String? = null

}

Using the @Ignore annotation, to try and ignore the local string on a generic update. Then provide a custom update statement to just save the local info

@Query("UPDATE foo SET local = :newLocal WHERE foo.id = :id")
fun updateLocal(id: Long, newLocal: String)

However ROOM seems to be smart enough to check that I used @Ignore on the local property and it will not compile with that update statement.

Any ideas?

Answer 1

Partial Updates got added to Room in 2.2.0

In Dao you do the following:

// Here you specify the target entity
@Update(entity = Foo::class)
fun update(partialFoo: PartialFoo)

And along your entity Foo create a PartialFoo containing the primary key and the fields you want to update.

@Entity 
class PartialFoo {
    @ColumnInfo(name = "id")
    val id: Long,

    @ColumnInfo(name = "thing1")
    val instructions: String,
}

https://stackoverflow.com/a/59834309/1724097