Extensions for using KeyPaths in Vapor4 Fluent migrations

SchemaBuilder_generic.swift

import Vapor
import Fluent

// Example models
final class Organization: Model, Content {
    static var schema = "organizations"
    
    @ID (key: .id)
    var id: UUID?
    
    @Field (key: "name")
    var name: String?
    
    @Children(for: \.$organization)
    var users: [User]
  
    init() {}
}

final class User: Model, Content {
    static var schema = "users"
    
    @ID (key: .id)
    var id: UUID?
    
    @Field (key: "name")
    var name: String?
    
    @Field (key: "email")
    var email: String?
    
    @OptionalParent (key: "org_id")
    var organization: Organization?
  
    init() {}
}



// Example migrations using the generic extensions
struct CreateOrgs: Migration {
    func prepare(on database: Database) -> EventLoopFuture<Void> {
        return database.schema(Organization.schema)
            .id()
            .field(\Organization.$name, .string, .required)
            .create()
    }
    
    func revert(on database: Database) -> EventLoopFuture<Void> {
        return database.schema(Organization.schema).delete()
    }
}

struct CreateUsers: Migration {
    func prepare(on database: Database) -> EventLoopFuture<Void> {
        return database.schema(User.schema)
            .id()
            .field(\User.$name,  .string)
            .field(\User.$email, .string, .required)
            .unique(on: \User.$email)
            .foreignKey(\User.$organization.$id, references: \Organization.$id, onDelete: .cascade, onUpdate: .cascade)
            .create()
    }
    
    func revert(on database: Database) -> EventLoopFuture<Void> {
        return database.schema(User.schema).delete()
    }
}



// Generic extensions allowing to use KeyPaths in migrations
extension SchemaBuilder {
    public func field<T, U>(
        _ key: KeyPath<T, U>,
        _ dataType: DatabaseSchema.DataType,
        _ constraints: DatabaseSchema.FieldConstraint...
    ) -> Self where T: Model, U: QueryableProperty {
        self.field(.definition(
            name: .key(T.path(for: key).last!),
            dataType: dataType,
            constraints: constraints
            ))
    }
    
    /// Passing multiple keypaths confuses the compiler, whereas one is fine.
    public func unique<T, U>(on fields: KeyPath<T, U>..., name: String? = nil) -> Self where T: Model, U: QueryableProperty {
        self.constraint(.constraint(
            .unique(fields: fields.map { .key(T.path(for: $0).last!) }),
            name: name
            ))
        return self
    }
    
    public func foreignKey<T, U, V, W>(
        _ field: KeyPath<T, V>,
        references foreignField: KeyPath<U, W>,
        onDelete: DatabaseSchema.ForeignKeyAction = .noAction,
        onUpdate: DatabaseSchema.ForeignKeyAction = .noAction,
        name: String? = nil
    ) -> Self where T:Model, U: Model, V: QueryableProperty, W: QueryableProperty {
        self.schema.createConstraints.append(.constraint(
            .foreignKey(
                [.key(T.path(for: field).last!)],
                U.schema,
                [.key(U.path(for: foreignField).last!)],
                onDelete: onDelete,
                onUpdate: onUpdate
            ),
            name: name
            ))
        return self
    }
    
    public func updateField<T, U>(
        _ key: KeyPath<T, U>,
        _ dataType: DatabaseSchema.DataType
    ) -> Self where T: Model, U: QueryableProperty {
        self.updateField(.dataType(
            name: .key(T.path(for: key).last!),
            dataType: dataType
            ))
    }
}

extension DatabaseSchema.FieldConstraint {
    public static func references<T, U>(
        _ field: KeyPath<T, U>,
        onDelete: DatabaseSchema.ForeignKeyAction = .noAction,
        onUpdate: DatabaseSchema.ForeignKeyAction = .noAction
    ) -> Self where T: Model, U: QueryableProperty {
        .foreignKey(
            T.schema,
            .key(T.path(for: field).last!),
            onDelete: onDelete,
            onUpdate: onUpdate
        )
    }
    
}

Updated for FluentKit 1.0.0-rc.2