Question

这是我模特的一个子集：

ServerWebsite
    desc Text
    url Text
    text Text
    username Text
    password Password
    serverDatabaseId ServerDatabaseId Maybe
    groupName Text Maybe
    serverId ServerId
    deriving Show Typeable
ServerDatabase
    desc Text
    name Text
    text Text
    username Text
    password Password
    groupName Text Maybe
    serverId ServerId
    deriving Show Typeable

我无法进行此查询构建：

filterServerWebsites :: SqlExpr (Value Text) -> SqlPersistM [Entity ServerWebsite]
filterServerWebsites query = select $ from $ \(w `LeftOuterJoin` db) -> do
    on (w ^. ServerWebsiteServerDatabaseId ==. db ?. ServerDatabaseId)
    where_ ((w ^. ServerWebsiteDesc `like` query)
        ||. (w ^. ServerWebsiteUrl `like` query)
        ||. (w ^. ServerWebsiteText `like` query)
        ||. (db ?. ServerDatabaseDesc `like` just query))
    return w

我不了解构建错误：

    • Couldn't match expected type ‘SqlQuery a1’
                  with actual type ‘(a0 -> b0) -> a0 -> a0 -> c0’
    • Probable cause: ‘on’ is applied to too few arguments
      In a stmt of a 'do' block:
        on (w ^. ServerWebsiteServerDatabaseId ==. db ?. ServerDatabaseId)

和

    • Couldn't match expected type ‘b0 -> b0 -> c0’
                  with actual type ‘SqlExpr (Value Bool)’
    • Possible cause: ‘(==.)’ is applied to too many arguments
      In the first argument of ‘on’, namely
        ‘(w ^. ServerWebsiteServerDatabaseId ==. db ?. ServerDatabaseId)’

我不明白我哪里出错了？

修改我从这段代码开始，它可以工作：

filterServerWebsites :: SqlExpr (Value Text) -> SqlPersistM [Entity ServerWebsite]
filterServerWebsites query = select $ from $ \w -> do
    where_ ((w ^. ServerWebsiteDesc `like` query)
        ||. (w ^. ServerWebsiteUrl `like` query)
        ||. (w ^. ServerWebsiteText `like` query))
    return w

Answer 1

右。所以真的是我自己的愚蠢。我应该制作一个样本项目来重现这个问题，然后我会发现这个问题。

问题是我在文件顶部...

import Database.Esqueleto hiding (on)
import Data.Function

...因为我正在使用on中该文件Data.Function中的其他位置。

我把它改为......

import Database.Esqueleto
import qualified Data.Function as F

现在一切正常......

esqueleto：外连接不编译

1 个答案: