如何使用Fluent在Vapor 3的同一张表中进行两个JOIN查询？

arema 发表于 Dev

区域

这就是我想要做的（使用PostgreSQL）：

选择H.“名称”，A。“名称”

从“比赛” M

加入“团队” H ONM。“ homeTeamID” = H.id

加入“ Teams” A ON M.“ awayTeamID” = A.id

//This will give me an error

return Matches.query(on: request)
.join(\Teams.id, to: \Matches.homeTeamID)
.alsoDecode(Teams.self)
.join(\Teams.id, to: \Matches.awayTeamID)
.alsoDecode(Teams.self)

这是错误：

{

错误：是的，

原因：“表名“ Team”指定了多次”

}

任何帮助表示赞赏！谢谢！

Mixio

@arema，我尝试重现您的用例，并且Fluent也遇到类似的问题。我在Fluent的github上报告了这个问题：https : //github.com/vapor/fluent/issues/563

这是一种解决方法，但远非优雅。

// Requires conforming `Match` to hashable, Equatable.
func getMatches2Handler(_ req: Request) throws -> Future<[MatchObjects]> {
    return map(
        to: [MatchObjects].self,
        Match.query(on: req).join(\Team.id, to: \Match.homeTeamID).alsoDecode(Team.self).all(),
        Match.query(on: req).join(\Team.id, to: \Match.awayTeamID).alsoDecode(Team.self).all()
    ) { homeTuples, awayTuples in
        let homeDictionary = homeTuples.toDictionary()
        let awayDictionary = awayTuples.toDictionary()
        var matchObjectsArray: [MatchObjects] = []
        matchObjectsArray.reserveCapacity(homeDictionary.count)
        for (match, homeTeam) in homeDictionary {
            let awayTeam = awayDictionary[match]!
            matchObjectsArray.append(MatchObjects(match: match, homeTeam: homeTeam, awayTeam: awayTeam))
        }
        return matchObjectsArray
    }
}

//...

extension Array {
    func toDictionary<K,V>() -> [K:V] where Iterator.Element == (K,V) {
        return self.reduce([:]) {
            var dict:[K:V] = $0
            dict[$1.0] = $1.1
            return dict
        }
    }
}

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