CODEWITHSUNDEEP
vapor
KrzysiekS
KrzysiekS

Reputation: 35

Database seeding and Eager Loading in Vapor

This is my code to perform database seeding:

func prepare(on database: Database) -> EventLoopFuture<Void> {
       
       var citySaveResults: [EventLoopFuture<Void>] = []
       
       return User.query(on: database).first().flatMap({ user -> EventLoopFuture<Void> in
           
           guard let userId = user?.id else { return citySaveResults.flatten(on: database.eventLoop).transform(to: ()) }
           
           let cities = [
               City(id: UUID(), name: "London", isActive: true, createdAt: Date()),
               City(id: UUID(), name: "New York", isActive: true, createdAt: Date()),
               City(id: UUID(), name: "San Francisco", isActive: true, createdAt: Date()),
           ]
           
           for city in cities {
               city.plans.append(contentsOf: createPlans(cityId: city.id, userId: userId))
               citySaveResults.append(city.save(on: database))
           }
           
           return citySaveResults.flatten(on: database.eventLoop) .transform(to: ())
       })
   }

But it crash in line:

 city.plans.append(contentsOf: createPlans(cityId: city.id, userId: userId))

 Fatal error: Children relation not eager loaded, use $ prefix to access.

Can someone explain me how to use Eager Loading feature to avoid crash in this situation?

This is my City model:

final class City: Model {
    
    static let schema = "cities"
    
    @ID(key: .id) var id: UUID?
    
    @Field(key: "name") var name: String
    @Field(key: "isActive") var isActive: Bool
    
    @Children(for: \Plan.$city) var plans: [Plan]

    ...
}

Upvotes: 1

Views: 285

Answers (1)

0xTim
0xTim

Reputation: 5565

Eager loading is for loading only as the name suggests. To save children you need to save the parent first and then save the children separately.

    func prepare(on database: Database) -> EventLoopFuture<Void> {
       
       var citySaveResults: [EventLoopFuture<Void>] = []
       
       return User.query(on: database).first().flatMap { user -> EventLoopFuture<Void> in
           
           guard let userId = user?.id else { return citySaveResults.flatten(on: database.eventLoop).transform(to: ()) }
           
           let cities = [
               City(id: UUID(), name: "London", isActive: true, createdAt: Date()),
               City(id: UUID(), name: "New York", isActive: true, createdAt: Date()),
               City(id: UUID(), name: "San Francisco", isActive: true, createdAt: Date()),
           ]
           
           for city in cities {
               let saveResult = city.save(on: database).flatMap {
                   let plans = createPlans(cityId: city.id, userId: userId)
                   return plans.save(on: database)
               }
               citySaveResults.append(saveResult)
           }
           
           return citySaveResults.flatten(on: database.eventLoop) .transform(to: ())
       }
   }

Upvotes: 3

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