I am using Room Persistence Library and I am trying to avoid boilerplate code by creating a Generic DAO class, like this
@Dao
public interface PendingTaskDao<V> {
@Query("SELECT * FROM :tableName")
Maybe<List<V>> getAllEntitiesFrom(String tableName);
}
But the compiler complains <table or subquery> expected got : tableName. Is there a way to create Generic DAO, or the library must work that way in order to prevent SQL injection?
the library must work that way in order to prevent SQL injection, yes, you're right.
From the docs of @Query:
This query is verified at compile time by Room to ensure that it compiles fine against the database.
So to let the query compile correctly, you must provide a tableName, not as a parameter, but directly in the query, hardcoded
Though, you cannot create a generic DAO for all the operations for all the entities, you can at least create a BaseDao to commonize the insert, insertAll, update, updateAll, delete, and deleteAll operations.
/**
* Created by Yousuf Sohail on 10/7/18.
*/
interface BaseDao<T> {
/**
* Insert an object or array of objects in the database.
*
* @param obj the objects to be inserted.
*/
@Insert(onConflict = OnConflictStrategy.REPLACE)
fun insert(vararg obj: T): LongArray
/**
* Update an object or array of objects from the database.
*
* @param obj the object to be updated
*/
@Update
fun update(vararg obj: T)
/**
* Delete an object or array of objects from the database
*
* @param obj the object to be deleted
*/
@Delete
fun delete(vararg obj: T)
}
select and selectAll will go to specific Daos of entities.
