我需要从Expense对象获取值字段的总和,并将其显示在textview中,但是我真的不知道如何在Room Database中进行操作。我需要在Dao中创建特定的查询,还是有其他方法?
Pojo:
@Entity(tableName = "expense_table")
public class Expense {
@PrimaryKey
private int id;
private String note;
private Double value;
private String type;
道:
@Dao
public interface ExpenseDao {
@Insert
void insertExpense(Expense expense);
@Query("SELECT * FROM expense_table")
LiveData<List<Expense>> getExpensesByDay();
答案 0 :(得分:2)
您需要在DAO中创建一个新查询
@Query("SELECT COALESCE(sum(COALESCE(value,0)), 0) From expense_table")
LiveData<Double> getTotal();