具有多个 parentColumn 和 entityColumn 的 Android 房间关系

Posted 2023-04-13

【中文标题】具有多个 parentColumn 和 entityColumn 的 Android 房间关系

【英文标题】：Android Room Relations with multiple parentColumn and entityColumn

【发布时间】：2019-02-06 14:48:50

【问题描述】：

假设您有一个 Room 数据库，其中包含两个使用外键关联的表（实体）。 （这只是一个简化的例子，所以不需要提出新的数据结构:)）

@Entity(tableName = "Streets", primaryKeys = "Country", "City")
public class Street 
...


@Entity(tableName = "Users",
    primaryKeys = "Country", "City", "Name",
    foreignKeys = @ForeignKey(entity = Street.class,
            parentColumns = "Country", "City",
            childColumns = "Country", "City",
            onDelete = CASCADE))
public class User 
...

如何在一次查询中检索数据库中的所有信息？ 下面的工作几乎与预期一样，但我还需要添加 City 列，但是如何做到这一点？ 如何添加多个parentColumn和entityColumn？

@Query("SELECT * FROM Streets")
public abstract LiveData<List<PoJo>> getAllUsers();

public static class PoJo 
    @Embedded
    private Street street;
    @Relation(parentColumn = "Country", entityColumn = "Country")
    private List<User> mUsers;

【参考方案1】：

此答案不会解决使用 Room 的问题。我们使用的是 SQLite，因此代码需要为 Room 设置样式。这段代码在 Kotlin 首先是两个模型类 ParentModel 和 ChildModel

data class ParentModel (
    val title : String = "",
    val children : List<ChildModel>
)

data class ChildModel(
    val image : Int = -1,
    val title : String = ""
)

旁注我们没有使用图像，因此很容易松动 现在这两个Adapter YEA Parent和Child没有创意命名

class ChildAdapter(private val children : List<ChildModel>)
: RecyclerView.Adapter<ChildAdapter.ViewHolder>()

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder 
    val v =  LayoutInflater.from(parent.context)
                  .inflate(R.layout.child_recycler,parent,false)
    return ViewHolder(v)


override fun getItemCount(): Int 
    return children.size


override fun onBindViewHolder(holder: ViewHolder, position: Int) 
    val child = children[position]
    holder.imageView.setImageResource(child.image)
    holder.textView.text = child.title



inner class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView)

    val textView : TextView = itemView.child_textView
    val imageView: ImageView = itemView.child_imageView




class ParentAdapter(private val parents : List<ParentModel>) : RecyclerView.Adapter<ParentAdapter.ViewHolder>()

private val viewPool = RecyclerView.RecycledViewPool()

override fun onCreateViewHolder(parent: ViewGroup, viewType: Int): ViewHolder 
    val v = LayoutInflater.from(parent.context).inflate(R.layout.parent_recycler,parent,false)
    return ViewHolder(v)


override fun getItemCount(): Int 
   return parents.size


override fun onBindViewHolder(holder: ViewHolder, position: Int) 
    val parent = parents[position]
    holder.textView.text = parent.title
    holder.recyclerView.apply 
        layoutManager = LinearLayoutManager(holder.recyclerView.context, LinearLayout.HORIZONTAL, false)
        adapter = ChildAdapter(parent.children)
        recycledViewPool = viewPool
    



inner class ViewHolder(itemView : View) : RecyclerView.ViewHolder(itemView)
    val recyclerView : RecyclerView = itemView.rv_child
    val textView:TextView = itemView.textView

注意在 ParentAdapter 中，ChildAdapter 必然会将信息带过来 现在 XML 关联文件首先是父文件，然后是子文件

<android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:card_view="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/card_view"
android:layout_
android:layout_
android:layout_gravity="center"
android:layout_margin="2dp"
card_view:cardBackgroundColor="#fff"
card_view:cardCornerRadius="5dp"
card_view:cardElevation="4dp"
card_view:cardUseCompatPadding="true">

<RelativeLayout
    android:layout_
    android:layout_
    android:orientation="vertical">

    <TextView
        android:id="@+id/textView"
        style="@style/Base.TextAppearance.AppCompat.Subhead"
        android:layout_
        android:layout_
        android:layout_alignParentTop="true"
        android:layout_alignStart="@+id/rv_child"
        android:padding="20dp"
        android:text="Hello World"
        android:textColor="@color/colorAccent"
        android:textStyle="bold" />

    <android.support.v7.widget.RecyclerView
        android:id="@+id/rv_child"
        android:layout_
        android:layout_
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:padding="20dp"
        android:layout_marginTop="30dp"
        android:orientation="horizontal"
        tools:layout_editor_absoluteX="74dp" />

</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:orientation="horizontal"
    android:layout_
    android:layout_>

    <TextView
        android:id="@+id/child_textView"
        android:layout_
        android:layout_
        android:layout_alignParentStart="true"
        android:layout_alignParentTop="true"
        android:layout_marginBottom="8dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="1dp"
        android:background="@android:color/darker_gray"
        android:padding="10dp"
        android:text="TextView"
        android:textColor="@android:color/white"
        android:textStyle="bold"
        app:layout_constraintBottom_toTopOf="@id/child_imageView"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="0.0" />

    <ImageView
        android:id="@+id/child_imageView"
        android:layout_
        android:layout_
        android:layout_marginBottom="38dp"
        android:layout_marginEnd="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="42dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="1.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:layout_constraintVertical_bias="1.0"
        app:srcCompat="@drawable/aviator" />

</android.support.constraint.ConstraintLayout>

以及调用获取数据的SQLite代码（我们还没有编写Activity来实现视图）

fun getDepartments(): List<ParentModel>
    val cursor = writableDatabase.query(DEPARTMENTS, arrayOf(ID, TITLE), null, null,
        null, null, ID)
    val list = mutableListOf<ParentModel>()
    if (cursor != null) 
        cursor.moveToFirst()
        while (!cursor.isAfterLast)
            val departmentId = cursor.getLong(cursor.getColumnIndex(ID))
            val items = getItems(departmentId)
            val d = ParentModel(cursor.getString(cursor.getColumnIndex(TITLE)), items)
            list.add(d)
            cursor.moveToNext()
        
        cursor.close()
    
    return list