具有多个parentColumn和entityColumn的Android Room关系
假设您有一个房间数据库,其中有两个表(实体),它们使用外键进行关联。(这只是一个简化的示例,因此无需提出新的数据结构:)) 如何在一次查询中检索数据库中的所有信息? 下面的工作几乎和预期的一样,但我也需要添加City列,但如何才能做到这一点? 如何添加多个parentColumn和entityColumn具有多个parentColumn和entityColumn的Android Room关系,android,android-room,android-database,Android,Android Room,Android Database,假设您有一个房间数据库,其中有两个表(实体),它们使用外键进行关联。(这只是一个简化的示例,因此无需提出新的数据结构:)) 如何在一次查询中检索数据库中的所有信息? 下面的工作几乎和预期的一样,但我也需要添加City列,但如何才能做到这一点? 如何添加多个parentColumn和entityColumn @Query("SELECT * FROM Streets") public abstract LiveData<List<PoJo>> getAllUsers();
@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;
}
@Query(“从街道选择*)
公共抽象LiveData getAllUsers();
公共静态类PoJo{
@嵌入
私家街;;
@关系(parentColumn=“Country”,entityColumn=“Country”)
私人博物馆名单;
}
此答案不会解决房间使用问题。我们使用的是SQLite,所以代码需要根据房间的需要进行样式化。此代码在Kotlin中首先是两个模型类ParentModel和ChildModel
data class ParentModel (
val title : String = "",
val children : List<ChildModel>
)
data class ChildModel(
val image : Int = -1,
val title : String = ""
)
数据类父模型(
val title:String=“”,
val子项:列表
)
数据类子模型(
val image:Int=-1,
val title:String=“”
)
旁注:我们没有使用图像,因此很容易丢失现在的两个适配器是父代和子代,没有创造性的命名
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
}
}
class ChildAdapter(私有val子项:列表)
:RecyclerView.Adapter(){
override onCreateViewHolder(父级:ViewGroup,viewType:Int):ViewHolder{
val v=LayoutInflater.from(parent.context)
.充气(右布局、儿童回收器、家长、假)
返回视窗支架(v)
}
重写getItemCount():Int{
返回大小
}
覆盖BindViewHolder(holder:ViewHolder,位置:Int){
val child=子对象[位置]
holder.imageView.setImageResource(child.image)
holder.textView.text=child.title
}
内部类ViewHolder(itemView:View):RecyclerView.ViewHolder(itemView){
val textView:textView=itemView.child\u textView
val imageView:imageView=itemView.child\u imageView
}
}
类ParentAdapter(private val parents:List):RecyclerView.Adapter(){
private val viewPool=RecyclerView.RecycledViewPool()
override onCreateViewHolder(父级:ViewGroup,viewType:Int):ViewHolder{
val v=LayoutFlater.from(parent.context)。充气(R.layout.parent\u recycler,parent,false)
返回视窗支架(v)
}
重写getItemCount():Int{
返回大小
}
覆盖BindViewHolder(holder:ViewHolder,位置:Int){
val parent=父项[位置]
holder.textView.text=parent.title
holder.recyclerView.apply{
layoutManager=LinearLayoutManager(holder.recyclerView.context,LinearLayout.HORIZONTAL,false)
adapter=ChildAdapter(parent.children)
recycledViewPool=viewPool
}
}
内部类ViewHolder(itemView:View):RecyclerView.ViewHolder(itemView){
val recyclerView:recyclerView=itemView.rv_子项
val textView:textView=itemView.textView
}
}
请注意,在ParentAdapter中,ChildAdapter将绑定信息现在,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_width="match_parent"
android:layout_height="wrap_content"
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_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/textView"
style="@style/Base.TextAppearance.AppCompat.Subhead"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
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_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
android:padding="20dp"
android:layout_marginTop="30dp"
android:orientation="horizontal"
tools:layout_editor_absoluteX="74dp" />
</RelativeLayout>
以及要调用以获取数据的SQLite代码(我们还没有编写实现视图的活动)
fun getDepartments():列表{
val cursor=writeabledatabase.query(部门、数组(ID、标题)、null、null、,
空,空,ID)
val list=mutableListOf()
如果(光标!=null){
cursor.moveToFirst()
而(!cursor.isAfterLast){
val departmentId=cursor.getLong(cursor.getColumnIndex(ID))
val items=getItems(部门ID)
val d=ParentModel(cursor.getString(cursor.getColumnIndex(TITLE)),items)
列表.添加(d)
cursor.moveToNext()
}
cursor.close()
}
返回列表
}
<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_width="match_parent"
android:layout_height="wrap_content"
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_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<TextView
android:id="@+id/textView"
style="@style/Base.TextAppearance.AppCompat.Subhead"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
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_width="match_parent"
android:layout_height="wrap_content"
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_width="wrap_content"
android:layout_height="wrap_content">
<TextView
android:id="@+id/child_textView"
android:layout_width="129dp"
android:layout_height="37dp"
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_width="126dp"
android:layout_height="189dp"
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>
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
}