Swift 在 Vapor 4 中使用协议的通用流利查询

我有几个型号的日期字段的名称相同，如下所示:

final class ModelA: Model {

static let schema = "model_a"

@Timestamp(key: "modification_date", on: .update, format: .unix)
var modificationDate: Date?

}

final class ModelB: Model {

static let schema = "model_b"

@Timestamp(key: "modification_date", on: .update, format: .unix)
var modificationDate: Date?

}

final class ModelC: Model {

static let schema = "model_c"

@Timestamp(key: "modification_date", on: .update, format: .unix)
var modificationDate: Date?

}

在我的代码中的某个点上，我希望获得最近更改的模型.所以我可以写下这样的东西:

func getRecentlyChangedModelAs(on db: Database) async throws -> [ModelA] {
   return try await ModelA.query(on: db)
                          .group(.and) { group in
                             group.filter(\.$modificationDate != nil)
                             group.filter(\.$modificationDate > Date.now.addingTimeInterval(TimeInterval(-3600)))
                          }
                          .all()
}

func getRecentlyChangedModelBs(on db: Database) async throws -> [ModelB] {
   return try await ModelB.query(on: db)
                          .group(.and) { group in
                             group.filter(\.$modificationDate != nil)
                             group.filter(\.$modificationDate > Date.now.addingTimeInterval(TimeInterval(-3600)))
                          }
                          .all()
}

func getRecentlyChangedModelCs(on db: Database) async throws -> [ModelC] {
   return try await ModelC.query(on: db)
                          .group(.and) { group in
                             group.filter(\.$modificationDate != nil)
                             group.filter(\.$modificationDate > Date.now.addingTimeInterval(TimeInterval(-3600)))
                          }
                          .all()
}

正如您所看到的，有很多代码重复.为了避免这种情况，我try 使用协议和通用查询:

protocol ModifiableModel: Model, Content {
    var modificationDate: Date? { set get }
}

final class ModelA: ModifiableModel {

static let schema = "model_a"

@Timestamp(key: "modification_date", on: .update, format: .unix)
var modificationDate: Date?

}

etc...

func getRecentlyChangedModel<T: ModifiableModel>(on db: Database) async throws -> [T] {
   return try await T.query(on: db)
                     .group(.and) { group in
                        group.filter(\.$modificationDate != nil) // Errors: 'nil' is not compatible with expected argument type 'KeyPath<Right, RightField>', Generic parameter 'RightField' could not be inferred
                        group.filter(\.$modificationDate > Date.now.addingTimeInterval(TimeInterval(-3600))) // Errors: Cannot convert value of type 'Date' to expected argument type 'KeyPath<Right, RightField>', No exact matches in call to instance method 'filter'
                      }
                      .all()

遗憾的是，这会在查询的过滤器中导致错误.我不太理解这些错误，但我发现没有过滤器，一切都编译得很好.我最好的猜测是，这些错误与我试图在筛选器中使用的关键路径有关.

有人知道问题出在哪里或如何解决吗？或者，有没有其他方法可以用来避免这种代码重复？任何帮助都将不胜感激！