Room - Schema export directory is not provided to the annotation processor so we cannot export the schema

I am using Android Database Component Room

I've configured everything, but when I compile, Android Studio gives me this warning:

> 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.

As I understand it is the location where DB file will be located

How can it affect my app? What is the best practice here? Should I use the default location (false value)?

As per the docs:

> You can set annotation processor argument (room.schemaLocation) to tell Room to export the schema into a folder. Even though it is not mandatory, it is a good practice to have version history in your codebase and you should commit that file into your version control system (but don't ship it with your app!).

So if you don't need to check the schema and you want to get rid of the warning, just add exportSchema = false to your RoomDatabase, as follows.

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

If you follow @mikejonesguy answer below, you will follow the good practice mentioned in the docs :). Basically you will get a .json file in your ../app/schemas/ folder. And it looks something like this:

{
  "formatVersion": 1,
  "database": {
    "version": 1,
    "identityHash": "53db508c5248423325bd5393a1c88c03",
    "entities": [
      {
        "tableName": "sms_table",
        "createSql": "CREATE TABLE IF NOT EXISTS `${TABLE_NAME}` (`id` INTEGER PRIMARY KEY AUTOINCREMENT, `message` TEXT, `date` INTEGER, `client_id` INTEGER)",
        "fields": [
          {
            "fieldPath": "id",
            "columnName": "id",
            "affinity": "INTEGER"
          },
          {
            "fieldPath": "message",
            "columnName": "message",
            "affinity": "TEXT"
          },
          {
            "fieldPath": "date",
            "columnName": "date",
            "affinity": "INTEGER"
          },
          {
            "fieldPath": "clientId",
            "columnName": "client_id",
            "affinity": "INTEGER"
          }
        ],
        "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, \"53db508c5248423325bd5393a1c88c03\")"
    ]
  }
}

If my understanding is correct, you will get such a file with every database version update, so that you can easily follow the history of your db.

In the build.gradle file for your app module, add this to the defaultConfig section (under the android section). This will write out the schema to a schemas subfolder of your project folder.

javaCompileOptions {
	annotationProcessorOptions {
		arguments += ["room.schemaLocation": "$projectDir/schemas".toString()]
	}
}

Like this:

// ...

android {
	
	// ... (compileSdkVersion, buildToolsVersion, etc)

    defaultConfig {

        // ... (applicationId, miSdkVersion, etc)
        
        javaCompileOptions {
            annotationProcessorOptions {
                arguments += ["room.schemaLocation": "$projectDir/schemas".toString()]
            }
        }
    }
   
    // ... (buildTypes, compileOptions, etc)

}

// ...

Kotlin? Here we go:

android {

    // ... (compileSdkVersion, buildToolsVersion, etc)

    defaultConfig {

        // ... (applicationId, miSdkVersion, etc)

        kapt {
    	    arguments {
    		    arg("room.schemaLocation", "$projectDir/schemas")
    	    }
        }
    }

    buildTypes {
        // ... (buildTypes, compileOptions, etc)
    }
}

//...

Don't forget about plugin:

apply plugin: 'kotlin-kapt'

For more information about kotlin annotation processor please visit: Kotlin docs

Above answers are correct. This version is easy to follow:

Because "Schema export directory is not provided to the annotation processor", So we need to provide the directory for schema export:

> Step [1] In your file which extends the RoomDatabase, change the line to:

`@Database(entities = ???.class,version = 1, exportSchema = true)`

Or

`@Database(entities = ???.class,version = 1)` 

(because the default value is always true)

> Step [2] In your build.gradle(project:????) file, inside the defaultConfig{ } (which is inside android{ } big section), add the javaCompileOptions{ } section, it will be like:

         android{
                defaultConfig{
                      //javaComplieOptions SECTION
                      javaCompileOptions {
                            annotationProcessorOptions {
                                     arguments = ["room.schemaLocation":"$projectDir/schemas".toString()]
                            }
                       }
                      //Other SECTION
                      ...
                }
         }

$projectDir:is a variable name, you cannot change it. it will get your own project directory

schemas:is a string, you can change it to any you like. For example: "$projectDir/MyOwnSchemas".toString()

@mikejonesguy answer is perfect, just in case you plan to test room migrations (recommended), add the schema location to the source sets.

> In your build.gradle file you specify a folder to place these > generated schema JSON files. As you update your schema, you’ll end up > with several JSON files, one for every version. Make sure you commit > every generated file to source control. The next time you increase > your version number again, Room will be able to use the JSON file for > testing. > > - Florina Muntenescu (source)

build.gradle

android {
    
    // [...]

    defaultConfig {
        
        // [...]

        javaCompileOptions {
            annotationProcessorOptions {
                arguments = ["room.schemaLocation": "$projectDir/schemas".toString()]
            }
        }
    }

    // add the schema location to the source sets
    // used by Room, to test migrations
    sourceSets {
        androidTest.assets.srcDirs += files("$projectDir/schemas".toString())
    }

    // [...]
}

I use .kts Gradle files (Kotlin Gradle DSL) and the kotlin-kapt plugin but I still get a script compilation error when I use Ivanov Maksim's answer.

Unresolved reference: kapt

For me this was the only thing which worked:

android {
    defaultConfig {
        javaCompileOptions {
            annotationProcessorOptions {
                arguments = mapOf("room.schemaLocation" to "$projectDir/schemas")
            }
        }
    }
}

For Kotlin KSP:

ksp {
    arg('room.schemaLocation', "$projectDir/schemas")
}

If like me you recently moved certain classes to different packages ect. and you use android navigation. Make sure to change the argType to you match you new package address. from:

app:argType="com.example.app.old.Item" 

to:

app:argType="com.example.app.new.Item" 

Kotlin way according to official document:

android {
...
defaultConfig {
    ...
    javaCompileOptions {
        annotationProcessorOptions {
            arguments += mapOf(
                "room.schemaLocation" to "$projectDir/schemas",
                "room.incremental" to "true",
                "room.expandProjection" to "true"
            )
        }
    }
}
}

Probably you didn't add your room class to child RoomDatabase child class in @Database(entities = {your_classes})