Android，如何检查 Room DB 中是否已存在列？

Question

How can I check if a specific column entry already exists in Room database?

For example, I have id as primary key. But also there is a column "username" which is also unique. So I want to check and see if a specific username like "Marshal" already exists in database to warn user about it.

Answer 1

All you have to do is create a Query like so:

@Query("SELECT COUNT(username) FROM MY_ENTITY WHERE username = :username")
fun getUsername(username: String) : LiveData<Integer>

If the result is 0 then there is no user with the same name if not you'll get the number of people with the same username.