Android 架构组件之Room数据库处理Schema export Error

柔情只为你懂 2022-06-04 05:44 1048阅读 0赞

在使用 Android Room数据库的时候，虽然项目可以运行起来。

但是，却报以下error:

Error:(22, 17) 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.

实际上，上面已经提示了开发者应该怎么处理，给出了两种方案。

--------------------

**解决方式一**：

给RoomDatabase设置exportSchema注解为false。

@Database(entities = { YourEntity.class }, version = 1, exportSchema = false)
    public abstract class MovieDatabase extends RoomDatabase { 
    
       ...
    
    }

**解决方案二**：

在项目中gradle中通过 annotationProcessorOptions 注解，为`room.schemaLocation`指定schemas的子文件夹。

android {
        compileSdkVersion 26
        buildToolsVersion "26.0.2"
        defaultConfig {
            applicationId "com.xingen.architecturecomponents"
            minSdkVersion 15
            targetSdkVersion 26
            versionCode 1
            versionName "1.0"
            testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
    
            //指定room.schemaLocation生成的文件路径
            javaCompileOptions {
                annotationProcessorOptions {
                    arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
                }
            }
        }
    
    }

当执行项目后，在Android Studio 的Project视图下，查看项目，会发现Module生成了一个schemas的文件夹，如下图所示：

![这里写图片描述][SouthEast]

其中，会生成版本1的Json文件,这里可以查看Room数据库的配置情况：

{
      "formatVersion": 1,
      "database": { "version": 1, "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\")" ] } }

#### **以上项目案例的连接**： [https://github.com/13767004362/ArchitectureComponentsDemo][https_github.com_13767004362_ArchitectureComponentsDemo] ####

--------------------

**资源参考**：

*  [https://stackoverflow.com/questions/44322178/room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we][https_stackoverflow.com_questions_44322178_room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we]

[SouthEast]: /images/20220604/475cdcf3678149cdbed575a0821f974a.png
[https_github.com_13767004362_ArchitectureComponentsDemo]: https://github.com/13767004362/ArchitectureComponentsDemo
[https_stackoverflow.com_questions_44322178_room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we]: https://stackoverflow.com/questions/44322178/room-schema-export-directory-is-not-provided-to-the-annotation-processor-so-we