Question

我正在尝试使用Google在I / O 2017中引入的Android Room Persistence（一种ORM）来设计和实现Android SQLite中的文件夹树结构。在我的设计中，文件夹可以包含其他文件夹和文件。以下是我的文件夹和文件代码：

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;
}

其父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<Folder> getAll();

    @Query("SELECT * FROM folders WHERE id IN (:folderIds)")
    List<Folder> 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);

        }
    });

得到此错误：

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)

有没有人知道什么是错的或建议我的项目表的另一个设计？

Answer 1

我让这个工作，但没有使用firewall-cmd --zone=external --permanent --add-masquerade firewall-cmd --zone=public --permanent --add-masquerade firewall-cmd --reload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int类，它使用Category作为主键：

UUID

现在你可以使用DAO方法：

/***
 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;
  }
}

Answer 2

我花了很长时间才弄清楚，即使是使用默认Kotlin数据类的uuid，也似乎根本不允许使用parentColumns元素作为自动生成的主键。像这样的值：

MyClass{
    //Don't do this
    @PrimaryKey(autoGenerate = true)
    var uuid: String = UUID.randomUUID()
}

始终确保您直接指定了父列。

Android Room FOREIGN KEY约束失败

2 个答案: