问题描述
我插入值的代码是:
def insert(link: entity.Link) : IO[Int] = {
logger.info("Inserting link: " + link.toString())
sql"insert into links (title,url,publication_date,feed_id) values (${link.getTitle},${link.getUrl},${link.getPublicationDate},${link.getFeed.getId})"
.update
.run
.transact(transactor)
}
调用它的方法是:
val links = for{
feeds <- getFeeds()
ls: List[Link] = feeds.flatMap(rssFeedReader.readFeedItems(_).asScala)
ios = ls.map(
link =>
linkPersistence
.countByUrl(link.getUrl())
.map(x => if(x==0) linkPersistence.insert(link) else identity(x))
)
s <- ios.sequence
}yield(s)
val result = links.unsafeRunSync()
logger.info("Result: " + result.toString())
不幸的是,我不能使用 For Expressions,因为 IO
没有 withFilter
并且我在 Maven 项目中(我正在将 Spring Boot 应用程序迁移到 Typelevel 堆栈),所以我不能使用改进的 For Expressions sbt 插件。
我的问题是行没有插入到数据库中。 日志上有:
reddit_bot_1 | 2021-04-23 13:06:57.805 INFO 1 --- [text-global-167] r.i.repository.LinkPersistence : Inserting link: Link{id=0,feed=Feed{id=79,url='https://ytali.com/feed/'},title='Se il grillo non fosse stato parlante',url='https://ytali.com/2021/04/21/se-il-grillo-non-fosse-stato-parlante/',publicationDate=Wed Apr 21 11:12:59 GMT 2021}
reddit_bot_1 | 2021-04-23 13:06:57.838 INFO 1 --- [text-global-167] r.i.repository.LinkPersistence : Inserting link: Link{id=0,feed=Feed{id=82,url='https://cronacheletterarie.com/feed/'},title='Scrivere come in una serie tv',url='https://www.cronacheletterarie.com/2021/04/22/scrivere-come-in-una-serie-tv-due-nuovi-thriller-italiani/',publicationDate=Thu Apr 22 06:50:30 GMT 2021}
reddit_bot_1 | 2021-04-23 13:06:57.993 INFO 1 --- [nio-8080-exec-1] reddit_bot.service.LinkUpdater : Result: List(1,1,IO$970148716,IO$398844220,IO$2051359159,IO$1102460161,IO$1646104176,IO$1525243662,IO$183629085,IO$2057291647,IO$1962915922,IO$1686018284,IO$1629671523,IO$1703036679,IO$1823891149,IO$2090799695,IO$189359223,IO$2089070694,IO$572184845,IO$638827115,IO$1723402242,IO$1063752499,IO$1262614371,IO$1882901634,IO$1592599455,IO$1561386362,IO$422495060,IO$1071010351,IO$135298961,IO$1395689700,IO$1022084533,IO$824291117,IO$977707631,IO$1835432555,IO$264428575,IO$858145293,IO$1014815708,IO$1654086426,IO$2074886515,IO$2048606753,IO$551801989,IO$2029261832,IO$1640654268,IO$1096825326,IO$2132380347,IO$664110340,IO$364966863,IO$1429149648,IO$1724908444,IO$1835403239,IO$2133511951,IO$1385617069,IO$876405632,IO$1773704159,IO$1078164304,IO$604307019,IO$2004298152,IO$1526495986,1)
交易者是这样创建的:
def transactor() = Transactor.fromDriverManager[IO](
"com.mysql.cj.jdbc.Driver","jdbc:mysql://database:3306/redditbot","redditbot","redditbot"
)
更新
按照@luis-miguel-mejía-suárez 的建议,我修改了我的 pom.xml
文件,如下所示:
<plugin>
<groupId>net.alchim31.maven</groupId>
<artifactId>scala-maven-plugin</artifactId>
<version>4.4.1</version>
<executions>
<execution>
<goals>
<goal>compile</goal>
<goal>testCompile</goal>
</goals>
</execution>
</executions>
<configuration>
<scalaVersion>${scala.version}</scalaVersion>
<sourceDir>src/main/scala</sourceDir>
<compilerPlugins>
<compilerPlugin>
<groupId>com.olegpy</groupId>
<artifactId>better-monadic-for_2.13</artifactId>
<version>0.3.1</version>
</compilerPlugin>
</compilerPlugins>
</configuration>
</plugin>
但问题依然存在。
解决方法
如@LuisMiguelMejíaSuárez 所写
正如错误明确指出的那样,IO 没有 withFilter
方法。 (You can check the scaladoc here)。当您明确输入类型时,您基本上是在过滤与此类类型匹配的所有元素。而且,由于该方法不存在,它不会编译。 - 不,我不知道任何解决方法。
但是,我至少可以想到一个不应该拥有它的原因。 IO 不完全是元素的“容器”,就像 List,因为它只是一个计算的描述,如果你把它看成一个容器,它会只有一个元素,比如 Option。但是,与前者不同的是,没有空IO的概念。因此,过滤 IO 没有意义。
我发现的解决方法是将过滤器移到另一个函数中:
def insertIfNotPresent(link: Link,foundLinksCount: Int): IO[Option[Int]] =
foundLinksCount match{
case 0 => linkPersistence.insert(link).map(Option(_))
case _ => IO.pure(None)
}
调用代码变为:
for{
foundLinksCount: Int <- linkPersistence.countByUrl(link.getUrl())
n: Option[Int] <- insertIfNotPresent(link,foundLinksCount)
}yield(n)