Android Room FOREIGN KEY约束失败

我试图在Android SQLite中设计和实现文件夹树结构,借助Google在I / O 2017中引入的Android Room Persistence(一种ORM)。在我的设计中,文件夹可以包含其他文件夹和文件。 这是我的文件夹和文件的代码:

文件模型:

@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 } 

这是文件夹代码:

 @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; } 

父ID的ID列上有一个外键。

这里是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 getAll(); @Query("SELECT * FROM folders WHERE id IN (:folderIds)") List loadAllByIds(int[] folderIds); } 

但是当我创建一个文件夹对象并尝试插入它时:

 AsyncTask.execute(new Runnable() { @Override public void run() { Folder folder = new Folder(); folder.setName("All"); DatabaseInstance.getInstance(getApplicationContext()).folderDAO().insertFolder(folder); } }); 

得到这个错误:

FOREIGN KEY约束失败

  --------- 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) 

有谁知道什么是错的或建议我的项目表的另一个设计?

我得到了这个工作,但没有使用int主键。 我不是那种ORM场景的粉丝,只是因为这些问题。

所以,这是一个自引用的Category类,它使用UUID作为其主键:

 /*** 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; } } 

现在您可以使用DAO方法:

 @Query("SELECT * FROM categories WHERE parentId IS NULL") Category findRootCategory(); @Query("SELECT * FROM categories WHERE parentId=:parentId") List findChildCategories(String parentId);