I have an android database with an entity something like

In other words, I want to use the autogenerated id to be included in a filename once the entity has been assigned. So I would like to do calls like

data.insert("cow")

and have it automatically assign an id and a filename of the form `"myfolder/" [id] ".mp3"

If I naively attempt to do this in the entity main method, with this.filename = "myfolder/" this.id ".mp3" then, since the id has not been set yet, this.id returns its null value (0).

Is it possible to do this?

CodePudding user response：

You can change the type of id to String and every time you insert a new item you generate a new UUID and set that UUID as id and filename, like that:

suspend fun insertItem(string: String) {
    val uuid = UUID.randomUUID().toString()
    val item = Item(
        id = uuid,
        string = string,
        fileName = "myFolder/$uuid.mp3"
    )
    dataDao.insert(item)
}

You can even pass that uuid as param to the insertItem function if you want to use it outside to generate a file or something:

suspend fun insertItem(string: String, uuid: String) {
    val item = Item(
        id = uuid,
        string = string,
        fileName = "myFolder/$uuid.mp3"
    )
    dataDao.insert(item)
}

CodePudding user response：

Well I can do this in the following way:

In the repository on the insert method (using a thread) we write

dataDao.insert(item)
dataDao.updateFilename()

where in the dao I have something like:

    @Query("UPDATE myTable SET filename = ('myfolder/' || id || '.mp3')")
    void updateFilename();

Of course, this means when we use a viewmodel to say myRepository.insert(item), we can include any filename in item - it will be overwritten in the corresponding repository method.

Obviously, whilst this will be fine for my small scale project, a better way to proceed is to introduce a separate method in the repository like void InsertWithAutomaticFilename or something which will be more transparent.

Perhaps somebody could agree or disagree with this way of proceeding? Or maybe there is a better way within the entity or dao itself?