隱式轉換的案例類問題

Question

我想隱式轉換一個案例類到另一個案例類，但不能讓代碼工作。我的編輯給了我Seq [LegacyPhase]不會轉換爲期望的Seq [Phase]的錯誤。任何人都可以指出我的方向嗎？提前致謝！

implicit def legacyToDashboardBrand(brand: LegacyDashboardBrand)(implicit session: Session): DashboardBrand = { 
    val phaseSeq: Seq[Phase] = (for { phaseDataset <- dashboardPhasesQ if phaseDataset.brandId === brand.id 
    } yield phaseDataset).list.toSeq 
    DashboardBrand(id = brand.id, projectId = brand.projectId, name = brand.name, currentPhase = brand.currentPhase, phases = phaseSeq) 
} 

implicit def legacyToDashboardPhase(phase: LegacyPhase): Phase = { 
    Phase(id = phase.id, brandId = phase.brandId, title = phase.title, steps = Seq()) 
} 

編輯：如果我在第一個隱式轉換定義中執行第二個隱式轉換行，它將起作用。

implicit def legacyToDashboardBrand(brand: LegacyDashboardBrand)(implicit session: Session): DashboardBrand = { 
    val legacyPhaseSeq = (for { 
    phaseDataset <- dashboardPhasesQ if phaseDataset.brandId === brand.id 
    } yield phaseDataset).list.toSeq 
    val phaseSeq: Seq[Phase] = legacyPhaseSeq.map(phase => 
    Phase(id = phase.id, brandId = phase.brandId, title = phase.title, steps = Seq()) 
) 

    DashboardBrand(id = brand.id, projectId = brand.projectId, name = brand.name, currentPhase = brand.currentPhase, phases = phaseSeq) 
} 

Answer 1

你的第二個解決方案（與複製代碼）的作品，因爲你明確地轉換Seq[LegacyPhase]爲Seq[Phase]。

你可以達到同樣的效果，通過在第一legacyToDashboardBrand功能增加一種隱含的參數爲您LegacyPhase => Phase轉換功能：

implicit def legacyToDashboardBrand(
    brand: LegacyDashboardBrand 
)(implicit 
    session: Session, 
    phaseConv: LegacyPhase => Phase 
): DashboardBrand = { 
    val phaseSeq: Seq[Phase] = (for { 
    phaseDataset <- dashboardPhasesQ if phaseDataset.brandId === brand.id 
    } yield phaseDataset).list.map(phaseConv).toSeq 
    DashboardBrand(
    id = brand.id, projectId = brand.projectId, name = brand.name, 
    currentPhase = brand.currentPhase, phases = phaseSeq 
) 
} 

這樣你LegacyDashboardBrand => DashboardBrand轉換功能，使用您的LegacyPhase => Phase轉換功能。

注意：我不認爲在隱式轉換函數中查詢數據庫不是一個好主意。隱式轉換本身非常「神奇」，並且使代碼更難理解，添加諸如查詢數據庫的副作用只會使其更加神奇。