Android房間FOREIGN KEY約束失敗

Question

我試圖在谷歌在I/O 2017中引入的Android Room Persistence（ORM）的幫助下，在Android SQLite中設計和實現文件夾樹結構。 在我的設計中，可以包含其他文件夾和文件。 這裏是我的文件夾和文件代碼：

文件型號：

@Entity(tableName = "files", foreignKeys = @ForeignKey(entity = Folder.class, 
    parentColumns = "id", 
    childColumns = "parent_id", 
    onDelete = CASCADE)) 
public class File { 
    @PrimaryKey(autoGenerate = true) 
    private int id; 

    private String title; 
    private Date creationDate; 

    @ColumnInfo(name = "parent_id") 
    public int parentId; 

    //here setters and getters skipped but exist in original code 
} 

這裏是文件夾代碼：

@Entity(tableName = "folders", foreignKeys = @ForeignKey(entity = Folder.class, 
    parentColumns = "id", 
    childColumns = "parent_id", 
    onDelete = CASCADE,onUpdate = SET_NULL)) 
public class Folder { 
    @PrimaryKey(autoGenerate = true) 
    private int id; 

    private String name; 

    @ColumnInfo(name = "parent_id") 
    private int parentId; 
} 

這對吧ID列的外鍵自父。

這裏是FolderDAO：

@Dao 
public interface FolderDAO { 
    @Insert(onConflict = OnConflictStrategy.REPLACE) 
    public void insertFolder(Folder... folders); 

    @Update 
    public void updateFolder(Folder... folders); 


    @Delete 
    public void deleteFolders(Folder... folders); 

    @Query("SELECT * FROM folders") 
    List<Folder> getAll(); 

    @Query("SELECT * FROM folders WHERE id IN (:folderIds)") 
    List<Folder> loadAllByIds(int[] folderIds); 
} 

但是當我做一個文件夾對象，並嘗試將其插入：

AsyncTask.execute(new Runnable() { 
     @Override 
     public void run() { 
      Folder folder = new Folder(); 
      folder.setName("All"); 

      DatabaseInstance.getInstance(getApplicationContext()).folderDAO().insertFolder(folder); 

     } 
    }); 

得到這個錯誤：

外鍵約束失敗

  --------- beginning of crash 
E/AndroidRuntime: FATAL EXCEPTION: AsyncTask #1 
       Process: sahraei.hamidreza.com.note, PID: 1835 
       android.database.sqlite.SQLiteConstraintException: FOREIGN KEY constraint failed (code 787) 
        at android.database.sqlite.SQLiteConnection.nativeExecuteForLastInsertedRowId(Native Method) 
        at android.database.sqlite.SQLiteConnection.executeForLastInsertedRowId(SQLiteConnection.java:782) 
        at android.database.sqlite.SQLiteSession.executeForLastInsertedRowId(SQLiteSession.java:788) 
        at android.database.sqlite.SQLiteStatement.executeInsert(SQLiteStatement.java:86) 
        at android.arch.persistence.db.framework.FrameworkSQLiteStatement.executeInsert(FrameworkSQLiteStatement.java:80) 
        at android.arch.persistence.room.EntityInsertionAdapter.insert(EntityInsertionAdapter.java:80) 
        at sahraei.hamidreza.com.note.DAO.FolderDAO_Impl.insertFolder(FolderDAO_Impl.java:80) 
        at sahraei.hamidreza.com.note.ItemListActivity$1.run(ItemListActivity.java:62) 
        at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231) 
        at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112) 
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587) 
        at java.lang.Thread.run(Thread.java:818) 

D任何人都知道什麼是錯的或者爲我的項目表提出了另一個設計？

Answer 1

我得到這個工作，但沒有使用int主鍵。僅僅因爲這些問題，我不是那種對這種ORM場景的狂熱粉絲。

所以，這裏是一個使用UUID其主鍵的自我指涉Category類：

/*** 
Copyright (c) 2017 CommonsWare, LLC 
Licensed under the Apache License, Version 2.0 (the "License"); you may not 
use this file except in compliance with the License. You may obtain a copy 
of the License at http://www.apache.org/licenses/LICENSE-2.0. Unless required 
by applicable law or agreed to in writing, software distributed under the 
License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS 
OF ANY KIND, either express or implied. See the License for the specific 
language governing permissions and limitations under the License. 
*/ 

package com.commonsware.android.room.dao; 

import android.arch.persistence.room.Entity; 
import android.arch.persistence.room.ForeignKey; 
import android.arch.persistence.room.Ignore; 
import android.arch.persistence.room.Index; 
import android.arch.persistence.room.PrimaryKey; 
import java.util.UUID; 
import static android.arch.persistence.room.ForeignKey.CASCADE; 

@Entity(
    tableName="categories", 
    foreignKeys=@ForeignKey(
    entity=Category.class, 
    parentColumns="id", 
    childColumns="parentId", 
    onDelete=CASCADE), 
    indices=@Index(value="parentId")) 
public class Category { 
    @PrimaryKey 
    public final String id; 
    public final String title; 
    public final String parentId; 

    @Ignore 
    public Category(String title) { 
    this(title, null); 
    } 

    @Ignore 
    public Category(String title, String parentId) { 
    this(UUID.randomUUID().toString(), title, parentId); 
    } 

    public Category(String id, String title, String parentId) { 
    this.id=id; 
    this.title=title; 
    this.parentId=parentId; 
    } 
} 

現在你可以有DAO的方法，如：

@Query("SELECT * FROM categories WHERE parentId IS NULL") 
Category findRootCategory(); 

@Query("SELECT * FROM categories WHERE parentId=:parentId") 
List<Category> findChildCategories(String parentId);