Yesod:通过Int从ID获取数据库实体 [英] Yesod: Getting a database entity by ID from an Int
问题描述
我对Haskell和Yesod都很陌生,并且正在尝试构建一个简单的Web应用程序,它可以回答来自外部API的查询。我已经构建了一个解析器(使用Parsec),它可以获取我想要作为常规Int值加载的实体的ID。
然而,我为了我无法弄清楚如何将这个Int变成 get
会接受的东西(即
任何帮助都将不胜感激,因为我好像被卡住了... :)
即使答案已经可以在评论中找到,我想举一个完整的例子。假设我们有一个 Person
Model,下面的函数返回给定ID的persion记录(如果存在的话) ):
import Database.Persist.Types(PersistValue(PersistInt64))
getByIntId :: Integral i =>我 - > Handler(也许是人)
getByIntId i = runDB $ get $ Key $ PersistInt64(fromIntegral i)
需要 import
来让我们构造一个整数的持久版本。 fromIntegral
将任何整数转换为期望的类型 Int64
。
更新:由于Yesod 1.2 PersistValue
存在于模块 Database.Persist.Types
中,在1.2之前它是 Database.Persist.Store
( API文档)。
更新2 :从Persistent 2.0.2开始,有两个内置函数可以将数据库键转换为数据库键: I'm new to both Haskell and Yesod, and am trying to build a simple web application that can answer queries from an external API. I have built a parser (using Parsec), that gets me the ID of an entity I want to load as a regular Int value. However, I for the life of me can't figure out how to turn this Int into something that Any help would be greatly appreciated, since I seem to be stuck... :) Even if the answer can already be found in the comments, I would like to give a complete example. Assuming we have a The Update: Since Yesod 1.2 Update 2: Since Persistent 2.0.2 there are two build-in functions to convert from/to database keys: 这篇关于Yesod:通过Int从ID获取数据库实体的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持IT屋! toSqlKey
和 fromSqlKey code>( API文档)。
get
will accept (i. e. a Key
(?)). All the examples in the documentation only get the id from previous inserts, or from url dispatch.Person
Model, the following function returns a record for the persion with the given ID (if it exists):import Database.Persist.Types (PersistValue(PersistInt64))
getByIntId :: Integral i => i -> Handler (Maybe Person)
getByIntId i = runDB $ get $ Key $ PersistInt64 (fromIntegral i)
import
is needed to let us construct the persist-version of an integer. fromIntegral
converts any integer to the expected type Int64
.PersistValue
lives in the module Database.Persist.Types
, before 1.2 it was Database.Persist.Store
(API Documentation).toSqlKey
and fromSqlKey
(API Documentation).