prisma 按关系排序只有 _count 属性。不能按关系字段排序

Question

考虑以下 Prisma 架构：

model Conversation {
  id           Int                         @id @default(autoincrement())
  createdAt    DateTime                    @db.Timestamp(6)
  messages     ConversationMessage[]
}

model ConversationMessage {
  id             Int                     @id @default(autoincrement())
  text           String                  @db.VarChar(1000)
  sentAt         DateTime                @map("sent_at") @db.Timestamp(6)
  conversationId Int?                    @map("conversation_id")
  userId         Int?                    @map("user_id")
  conversation   Conversation?           @relation(fields: [conversationId], references: [id])
  sender         User?                   @relation(fields: [userId], references: [id])
}

我想运行这样的查询，以便获得按消息日期排序的会话列表，即首先有新消息的会话。

prisma.conversation.findMany({
    orderBy: {
        messages: {
            sentAt: 'desc'
        }
    },
    ...
})

但我现在可以查询的唯一方法是这样，即关系在某种程度上只有_count 属性。

prisma.conversation.findMany({
    orderBy: {
        messages: {
           '_count': 'desc'
        }
     },
     ...
})

环境和设置

    OS: Mac OS,
    Database: PostgreSQL
    Node.js version: v12.19.0

棱镜版本

prisma               : 2.24.1
@prisma/client       : 2.24.1
Current platform     : darwin
Query Engine         : query-engine 18095475d5ee64536e2f93995e48ad800737a9e4 (at node_modules/@prisma/engines/query-engine-darwin)
Migration Engine     : migration-engine-cli 18095475d5ee64536e2f93995e48ad800737a9e4 (at node_modules/@prisma/engines/migration-engine-darwin)
Introspection Engine : introspection-core 18095475d5ee64536e2f93995e48ad800737a9e4 (at node_modules/@prisma/engines/introspection-engine-darwin)
Format Binary        : prisma-fmt 18095475d5ee64536e2f93995e48ad800737a9e4 (at node_modules/@prisma/engines/prisma-fmt-darwin)
Default Engines Hash : 18095475d5ee64536e2f93995e48ad800737a9e4
Studio               : 0.397.0
Preview Features     : orderByRelation

谢谢！

Answer 1

虽然 Prisma V2.19 引入了 sort by relation aggregate value，但在撰写本文时，唯一支持的聚合属性是 count。据我所知，目前 Prisma 不直接支持您的要求。如果他们添加 min 和 max 聚合属性进行排序，这是可能的。

一种可能的解决方法是在检索后对 Node.js 中的消息进行排序。我正在添加一个解决方案，该解决方案使用orderByRelation 预览功能来简化排序并确保对话中的消息始终按顺序排列（最新消息在前）。

更新 Prisma 客户端以使用 orderByRelation 预览功能。

首先更新schema.prisma添加预览功能

generator client {
  provider = "prisma-client-js"
  previewFeatures = ["orderByRelation"]
}

现在更新 prisma 客户端

prisma generate client   

获取conversations 并按最新消息对其进行排序

// Assuming inside an async function 

let unsortedConversations = await prisma.conversation.findMany({
    include: {
        messages: {
            orderBy: {    
                sentAt: 'desc'  // messages for each converastion will be ordered newest first. 
            }
        }
    },
    // other conditions
})

unsortedConversations 包含所有必需的对话，但它们是无序的。您可以通过创建自定义比较器函数按所需顺序对其进行排序。

function conversationComparatorFunction(conversationA, conversationB) {
    // Conversations with 0 messages will be placed last in arbitrary order. 
    if (!conversationB.messages.length) return 1;  
    if (!conversationA.messages.length) return -1;
    
    // sort conversations based on sentAt date of the first message. 
    // since messages were previously sorted, messages[0] always contain the most recent message. 
    if (conversationA.messages[0].sentAt > conversationB.messages[0].sentAt) {
        return -1;
    } else if (conversationA.messages[0].sentAt < conversationB.messages[0].sentAt) {
        return 1;
    } else return 0;

}

let sortedConversations = unsortedConversations.sort(conversationComparatorFunction)

但请注意，如果 Conversation 记录的数量非常在应用程序端排序可能会导致性能下降，尤其是考虑到 Node.js 是单线程的。

Answer 2

如果启用此预览功能，现在可以按一对多关系排序：

One-to-Many
For one-to-many relationships, you can order by the relation from one side:

✅ Order posts by their author's name

⛔️ Order authors by their post's titles

model Author {
  id Int @id
  name String
  posts Post[]
}

model Post {
  id Int @id
  title String
  author Author
}
prisma.post.findMany({
  orderBy: [{
    author: {
      name: 'asc'
    }
  }]
})

见https://github.com/prisma/prisma/issues/5008

Answer 3

OrderBy 关系仍然是一个预览功能 - 您需要确保使用功能标志

generator client {
  provider        = "prisma-client-js"
  previewFeatures = ["orderByRelation"]
}

https://www.prisma.io/docs/concepts/components/prisma-client/filtering-and-sorting#sort-by-relation-preview