Android 房间DB：UPSERT返回什么

使用@Upsert批注调用的函数/方法可以返回

1. 无/无效，或
2. 长/长，或
3. 长/长的数组(如果可能有多个插入).

• the returned value should be the rowid of the inserted or replaced row.
  • Rowid是一个通常隐藏的列，所有典型的Room表都有.
  • if the PRIMARY KEY is a single field/member 和 that field/member is an integer type (Long, Int, int, long even Boolean 和 so on) then the PRIMARY KEY will be an alias of the rowid 和 thus the PRIMARY KEY of the inserted row
  • if the PRIMARY KEY consists of multiple columns or is not a single integer type column then the rowid still exists 和 can be used
• it should be noted that Room does not use the SQLite UPSERT (at least currently) but uses an an SQLite INSERT OR REPLACE (和 hence returns the same values that an @Insert does).

通过编码和编译就可以很容易地确定

例如，使用

@Upsert
fun upsert(parent: PartCargo): Int

顶级编译失败，Not sure how to h和le upsert method's return type.

同时，

@Upsert
fun upsert(parent: PartCargo): Long

@Upsert
fun upsert(parent: PartCargo)

和

编译成功.

然而，

@Upsert
fun upsert(parent: PartCargo): LongArray

失败，错误为Upsert method accepts a single parameter but the return type is a collection of elements.

同时，

@Upsert
fun upsert(parents: List<PartCargo>): LongArray

编译成功.

• all the above are Kotlin, but Java is similar (hence void 和 long in the initial part of the answer).

Additional个

can you add a reference about Room's implementation of Upsert that behind the scene only do insert 和 replace before I accept this answer?

如果有参考文献，则不需要.实际上在"幕后"做了什么很容易确定.

The "behind the scenes", is the annotation processer generating java code. This java generated java code forms part of the package 和 is what is actually used at runtime.

The 2 core/primary annotations are the @Database 和 @Dao annotations. These determine the resultant classes that contain the respective generated java. The classes will be the name of the class/interface being processed suffixed with _Impl.

生成的Java放在文件夹的子文件夹中，通过Android Studio中的Android View显示为Java(生成的).通常会有两个同名的子文件夹.其中一个将被视为包含已生成的各个类.

例如，上述代码摘录摘自以下内容:

The extracts were from the @Dao annotated interface interface DetailsDAO .... 和 hence the DetailsDAO_Impl class that has been generated.

搜索Upsert找到:-

• 注意不要编辑文件的警告
  • 实际上，有时可以忽略，例如添加断点进行调试

It is then just a matter of ascertaining the respective code utilised 和 the SQL invoked. For the above the eventual respective code is:-

this.__insertionAdapterOfPartCargo = new EntityInsertionAdapter<PartCargo>(__db) {
      @Override
      @NonNull
      protected String createQuery() {
        return "INSERT OR REPLACE INTO `parts` (`tId`,`detailsTId`,`id`,`name`) VALUES (nullif(?, 0),?,?,?)";
      }