我如何在房间数据库Android中求和 [英] How can i sum value in room database android

问题描述

我想知道如何对房间数据库中的值求和.

I want to know that how can i sum value in the room database .

假设我已将此值(10,000)插入到会议室数据库中，并且我想向数据库(20,000)中插入新值，并且我希望新值与旧值相加而不替换它.

Let say i have insert this value (10,000) in the room database and i want to insert new value to database (20,000) and i want the new value to be sum with old value not replace it .

我该怎么做??

代码示例:

数据库表:

@entity 
class sum (

id : int , 
value : Long )

Dao :

@insert (onConflict = OnConflictStrategy.REPLACE)
suspend fun insert (model :sum)

what shoud i use instead of above insert . 


@Query("SELECT * FROM sum")

fun getall () : LiveData<sum>

和活动中:

late init var : viewmodel : Viewmodeldatabase 
val textvalue : TextView

viewmodel = Viewmodelprovider(this).get(Viewmodeldatabase::class.java)

textvalue = findvidwbyid(R.id.text)
viewmodel.insert(sum(1 , 10000)

// when the above value insert , if there is an old value sum with it and not replace it or remove it 

viewmodel.getall.observe(this , Observer {

textvalue.text = it.value


)}

谢谢大家观看我的代码并为我提供帮助.

thank's guys for watch my code and help me .

推荐答案

尝试在dao中添加下一个方法:

Try to add next method in your dao:

@Query("UPDATE sum SET value = value + :addValue WHERE id =:id")
suspend fun updateSum(id: Int, addValue: Long)

然后您可以从ViewModel/Activity中调用它

Then you can call it from your ViewModel/Activity

更新

对于用于更新/插入的单个方法，请将这些方法放在dao中:

For single method for update/insert put these methods in dao:

@Insert(onConflict = OnConflictStrategy.REPLACE)
suspend fun insertSum(model: Sum)

@Query("UPDATE sum SET value = value + :value WHERE id = :id")
suspend fun updateSum(id: Int, value: Long)

@Query("SELECT * FROM sum WHERE id = :id")
suspend fun getSumById(id: Int): Sum?

@Transaction
suspend fun updateOrInsertSum(sum: Sum) { // <-- this method updates value or insert new item, if id is not found
    getSumById(sum.id)?.let { updateSum(sum.id, sum.value) } ?: insertSum(sum)
}

当然，您还应该将方法updateOrInsertSum添加到存储库和viewmodel中 然后，如果您首次要求id ='1'，则会插入值:

Of course you should add method updateOrInsertSum to your repository and viewmodel as well Then if you call for id = '1' for the first time value will be inserted:

viewmodel.updateOrInsertSum(Sum(1 ,10000)) // <-- id = 1, value = 10000

在下一个通话项目上，将使用相同的方法进行更新:

On the next call item will be updated with the same method:

viewmodel.updateOrInsertSum(Sum(1 ,20000)) // <-- id = 1, value = 10000+2000 

这篇关于我如何在房间数据库Android中求和的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！