Android 架構元件之Room資料庫 處理Schema export Error

在使用 Android Room資料庫的時候，雖然項目可以運作起來。

但是，卻報以下error:

Error:(, ) 警告: Schema export directory is not provided to the annotation processor so we cannot export the schema. 

You can either provide `room.schemaLocation` annotation processor argument OR set exportSchema to false.
           

實際上，上面已經提示了開發者應該怎麼處理，給出了兩種方案。

解決方式一：

給RoomDatabase設定exportSchema注解為false。

@Database(entities = { YourEntity.class }, version = , exportSchema = false)
public abstract class MovieDatabase extends RoomDatabase {

   ...

}
           

解決方案二：

在項目中gradle中通過 annotationProcessorOptions 注解，為

room.schemaLocation

指定schemas的子檔案夾。

android {
    compileSdkVersion 
    buildToolsVersion "26.0.2"
    defaultConfig {
        applicationId "com.xingen.architecturecomponents"
        minSdkVersion 
        targetSdkVersion 
        versionCode 
        versionName "1.0"
        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

        //指定room.schemaLocation生成的檔案路徑
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
            }
        }
    }

}
           

當執行項目後，在Android Studio 的Project視圖下，檢視項目，會發現Module生成了一個schemas的檔案夾，如下圖所示：

其中，會生成版本1的Json檔案,這裡可以檢視Room資料庫的配置情況：

{
  "formatVersion": ,
  "database": {
    "version": ,
    "identityHash": "8240057b6178b803a0bf9915edf969ef",
    "entities": [
      {
        "tableName": "movies",
        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT NOT NULL, `year` TEXT, `title` TEXT, `image` TEXT)",
        "fields": [
          {
            "fieldPath": "id",
            "columnName": "id",
            "affinity": "INTEGER",
            "notNull": true
          },
          {
            "fieldPath": "year",
            "columnName": "year",
            "affinity": "TEXT",
            "notNull": false
          },
          {
            "fieldPath": "title",
            "columnName": "title",
            "affinity": "TEXT",
            "notNull": false
          },
          {
            "fieldPath": "image",
            "columnName": "image",
            "affinity": "TEXT",
            "notNull": false
          }
        ],
        "primaryKey": {
          "columnNames": [
            "id"
          ],
          "autoGenerate": true
        },
        "indices": [],
        "foreignKeys": []
      }
    ],
    "setupQueries": [
      "CREATE TABLE IF NOT EXISTS room_master_table (id INTEGER PRIMARY KEY,identity_hash TEXT)",
      "INSERT OR REPLACE INTO room_master_table (id,identity_hash) VALUES(42, \"8240057b6178b803a0bf9915edf969ef\")"
    ]
  }
}
           

以上項目案例的連接配接： https://github.com/13767004362/ArchitectureComponentsDemo

資源參考：

• https://stackoverflow.com/questions/44322178/room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we