在生成帖子的最新帖子列表时，如何避免依赖周期? [英] How do I avoid a dependency cycle when generating a list of recent posts on posts?

问题描述

这可行:

create ["archive.html"] $ do
    route idRoute
    compile $ do
        posts <- (myRecentFirst gitTimes) =<< loadAll "posts/**"
        let archiveCtx =
                listField "posts" (postCtx allTags allCategories gitTimes) (return posts) `mappend`
                constField "title" "Archives"            `mappend`
                (postCtx allTags allCategories gitTimes)

        makeItem ""
            >>= loadAndApplyTemplate "templates/archive.html" archiveCtx
            >>= loadAndApplyTemplate "templates/default.html" archiveCtx
            >>= relativizeUrls

在archive.html中创建最近发布的列表；这是沼泽标准的，它来自我认为的其中一篇教程.除了postsCtx之外，这有点复杂，但此处不相关.

to create a list of recent posts in archive.html ; this is bog-standard, it came from one of the tutorials I think. Except for postsCtx, which is a tad complicated, but shouldn't be relevant here.

但是，我想在普通帖子的侧边栏中列出一些最近的帖子.问题在于最近的帖子最终取决于他们自己.我尝试将帖子本身从自己的生成列表中排除，但找不到合适的位置.这是到目前为止我得到的:

However, I want to put a list of a few recent posts in the sidebar of normal posts. The problem becomes that the recent posts end up depending on themselves. I tried excluding the post itself from its own generated list, but I couldn't find a good place to do that. Here's what I've got so far:

match "posts/**" $ do
    route $ (gsubRoute "posts/" (const "")) `composeRoutes` setExtension "html"
    compile $ do
        recents <- (myRecentFirst gitTimes) =<< loadAll "posts/**"
        let postsContext = postCtx allTags allCategories gitTimes `mappend`
                           -- Show recent posts
                           recentsNotSelfField "recents" (postCtx allTags allCategories gitTimes) (return $ take 3 recents)

        pandocCompilerWithTransform hblogPandocReaderOptions hblogPandocWriterOptions (titleFixer titles)
            >>= loadAndApplyTemplate "templates/post.html"    postsContext
            >>= loadAndApplyTemplate "templates/default.html" postsContext
            >>= relativizeUrls

recentsNotSelfField :: String -> Context a -> Compiler [Item a] -> Context b
recentsNotSelfField key context items = Context $ \k _ i ->
    if k == key then do
        let myId = itemIdentifier i
        strippedItems <- items
        let remains = filter (\x -> (itemIdentifier x) /= myId) strippedItems
        return $ ListField context remains
    else
        CA.empty

recentsNotSelfField 应该产生一个包含所有最新消息 except 本身的字段，但是它似乎不起作用或执行该操作的位置不正确，原因是:

recentsNotSelfField should produce a field with all the recents except itself, but it doesn't seem to be working or it's the wrong place to do that, because:

Initialising...
  Creating store...
  Creating provider...
  Running rules...
Checking for out-of-date items
Compiling
  [ERROR] Hakyll.Core.Runtime.chase: Dependency cycle detected: posts/computing/contact.md depends on posts/computing/contact.md

我被困住了.

我看到 Hakyll说检测到依赖性周期:..." ，它是由loadPosts完成的，所以我尝试了这一点:

I saw Hakyll says "Dependency cycle detected: ..." , that it's the loadPosts that does it, so I tried this:

match "posts/**" $ do
    route $ (gsubRoute "posts/" (const "")) `composeRoutes` setExtension "html"
    compile $ do
        myId <- getUnderlying
        recents <- (myRecentFirst gitTimes) =<< loadAll ("posts/**" .&&. complement (fromList [myId]))
        let postsContext = postCtx allTags allCategories gitTimes `mappend`
                           -- Show recent posts
                           listField "recents" (postCtx allTags allCategories gitTimes) (return $ take 3 recents)

        pandocCompilerWithTransform hblogPandocReaderOptions hblogPandocWriterOptions (titleFixer titles)
            >>= loadAndApplyTemplate "templates/post.html"    postsContext
            >>= loadAndApplyTemplate "templates/default.html" postsContext
            >>= relativizeUrls

但这让我明白了:

[ERROR] Hakyll.Core.Runtime.chase: Dependency cycle detected: posts/computing/contact.md depends on posts/computing/general/ched.md depends on posts/computing/contact.md

，换句话说，我最后经历了两个最近的循环.

, in other words I end up with the two most recent cycling around each other.

推荐答案

在 https://stackoverflow.com/a/35651294/1461430 对我有用，实际上，它对我来说比作者说的要好.这是我的代码的相关内容:

Turns out the technique at https://stackoverflow.com/a/35651294/1461430 works for me, and in fact it works better for me than the author said it would. Here's the relevant bits of my code now:

match "posts/**" $ version "recents" $ do
    route $ (gsubRoute "posts/" (const "")) `composeRoutes` setExtension "html"
    compile $ do
        pandocCompilerWithTransform hblogPandocReaderOptions hblogPandocWriterOptions (titleFixer titles)
            >>= loadAndApplyTemplate "templates/post.html"    (postCtx allTags allCategories gitTimes)
            >>= relativizeUrls

match "posts/**" $ do
    route $ (gsubRoute "posts/" (const "")) `composeRoutes` setExtension "html"
    compile $ do
        myId <- getUnderlying
        recents <- (myRecentFirst gitTimes) =<< loadAll ("posts/**" .&&. hasVersion "recents")
        let postsContext = postCtx allTags allCategories gitTimes `mappend`
                           -- Show recent posts
                           listField "recents" (postCtx allTags allCategories gitTimes) (return $ take 3 recents)

        pandocCompilerWithTransform hblogPandocReaderOptions hblogPandocWriterOptions (titleFixer titles)
            >>= loadAndApplyTemplate "templates/post.html"    postsContext
            >>= loadAndApplyTemplate "templates/default.html" postsContext
            >>= relativizeUrls

我不得不在使用template/default.html的其他几个地方添加listField和最近使用的内容，但这很简单.

I had to add the listField and recents to several other places that used templates/default.html, but that was straightforward.

我还必须修改一个使用标识符的函数，以查找从git提取的时间列表:

I also had to modify a function that used Identifier to look up a list of times pulled from git:

-- Pull a file's time out of the list
getGitTimeUTC :: Identifier -> [GitTimes] -> (GitTimes -> UTCTime) -> UTCTime
getGitTimeUTC ident times typeF =
  -- The identifier for the things compiled with the "recents"
  -- version has the identifierVersion "recents", but we don't care
  -- about that since the only reason that exists is to avoid loops,
  -- so we strip it here for our lookup.
  let fixedIdent = ident { identifierVersion = Nothing }
      timeList = filter (\x -> fixedIdent == (gtid x)) times in
    if length timeList /= 1 then
      -- It's not obvious to me how this could occur even in theory; I'd expect it to error out during getGitTimes
      error $ "getGitTimeUTC: Couldn't find the time for " ++ (show fixedIdent) ++ " in GitTimes list " ++ (show times)
    else
      typeF $ head timeList

因此，我没有文件重复，也没有链接到最新文件的问题.一切正常.

I have no duplication of files as a result, and had no problem making links to the recents files; everything just works.

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