我开始使用Room数据库,并浏览了一些文档来创建Room实体。这些是我的关系。聊天频道可以进行很多对话。因此,这是一对多关系。因此,我创建了如下实体。
频道实体
@Entity(primaryKeys = ["channelId"])
@TypeConverters(TypeConverters::class)
data class Channel(
@field:SerializedName("channelId")
val channelId: String,
@field:SerializedName("channelName")
val channelName: String,
@field:SerializedName("createdBy")
val creationTs: String,
@field:SerializedName("creationTs")
val createdBy: String,
@field:SerializedName("members")
val members: List<String>,
@field:SerializedName("favMembers")
val favMembers: List<String>
) {
// Does not show up in the response but set in post processing.
var isOneToOneChat: Boolean = false
var isChatBot: Boolean = false
}
对话实体
@Entity(primaryKeys = ["msgId"],
foreignKeys = [
ForeignKey(entity = Channel::class,
parentColumns = arrayOf("channelId"),
childColumns = arrayOf("msgId"),
onUpdate = CASCADE,
onDelete = CASCADE
)
])
@TypeConverters(TypeConverters::class)
data class Conversation(
@field:SerializedName("msgId")
val msgId: String,
@field:SerializedName("employeeID")
val employeeID: String,
@field:SerializedName("channelId")
val channelId: String,
@field:SerializedName("channelName")
val channelName: String,
@field:SerializedName("sender")
val sender: String,
@field:SerializedName("sentAt")
val sentAt: String,
@field:SerializedName("senderName")
val senderName: String,
@field:SerializedName("status")
val status: String,
@field:SerializedName("msgType")
val msgType: String,
@field:SerializedName("type")
val panicType: String?,
@field:SerializedName("message")
val message: List<Message>,
@field:SerializedName("deliveredTo")
val delivered: List<Delivered>?,
@field:SerializedName("readBy")
val read: List<Read>?
) {
data class Message(
@field:SerializedName("txt")
val txt: String,
@field:SerializedName("lang")
val lang: String,
@field:SerializedName("trans")
val trans: String
)
data class Delivered(
@field:SerializedName("employeeID")
val employeeID: String,
@field:SerializedName("date")
val date: String
)
data class Read(
@field:SerializedName("employeeID")
val employeeID: String,
@field:SerializedName("date")
val date: String
)
// Does not show up in the response but set in post processing.
var isHeaderView: Boolean = false
}
现在您可以看到对话属于频道。当用户看到频道列表时,我需要在列表项中显示Last Conversation的几个属性。我的问题是,如果我只是像上面那样声明关系还是在Channel类中包含Converstion对象就足够了吗?我还可以通过哪些其他方式处理它?因为当用户滚动时,UI需要在频道列表的每个项目中获取与时间,状态等一起发生的最新对话。因此,当我查询时,UI不应因此而滞后。
我如何在Channel对象中拥有最近的Converstaion对象?
我建议像这样创建另一个类(不在DB中,只是为了在UI中显示):
data class LastConversationInChannel(
val channelId: String,
val channelName: String,
val creationTs: String,
val createdBy: String,
val msgId: String,
val employeeID: String,
val sender: String,
val sentAt: String,
val senderName: String
.
.
.
)
通过此查询获取每个频道中的最后一个会话:
SELECT Channel.*
,IFNULL(LastConversation.msgId,'') msgId
,IFNULL(LastConversation.sender,'') sender
,IFNULL(LastConversation.employeeID,'') employeeID
,IFNULL(LastConversation.sentAt,'') sentAt
,IFNULL(LastConversation.senderName,'') senderName
from Channel left join
(SELECT * from Conversation a
WHERE a.msgId IN ( SELECT b.msgId FROM Conversation AS b
WHERE a.channelId = b.channelId
ORDER BY b.sentAt DESC LIMIT 1 )) as LastConversation
on Channel.channelId = LastConversation.channelId
然后像这样在您的dao中使用它:
@Query(" SELECT Channel.*\n" +
" ,IFNULL(LastConversation.msgId,'') msgId\n" +
" ,IFNULL(LastConversation.sender,'') sender\n" +
" ,IFNULL(LastConversation.employeeID,'') employeeID\n" +
" ,IFNULL(LastConversation.sentAt,'') sentAt\n" +
" ,IFNULL(LastConversation.senderName,'') senderName\n" +
" from Channel left join \n" +
" (SELECT * from Conversation a \n" +
" WHERE a.msgId IN ( SELECT b.msgId FROM Conversation AS b \n" +
" WHERE a.channelId = b.channelId \n" +
" ORDER BY b.sentAt DESC LIMIT 1 )) as LastConversation\n" +
" on Channel.channelId = LastConversation.channelId")
fun getLastConversationInChannel(): LiveData<List<LastConversationInChannel>>
如果我只是像上面那样声明关系,或者我应该在Channel类中包含Converstion对象,就足够了吗?
您不应该在Channel类中包含“对话”,因为Room将在“对话”表中为其创建一些列。
您可以在Chanel内部拥有一个LastConversation
,即Conversation object
。每次更新lastConversation时,都必须通过从“房间”层修改表Chanel来更新此内容。 (对于更新数据库而言,性能不高)。通过对香奈儿列表进行排序(可比较)。您的用户界面更新将很酷。 UI或ViewModel的逻辑更简单。我也是这样做的。