Crust

A flexible Swift framework for converting classes and structs to and from JSON with support for storage solutions such as Realm.

Features 🎸

• Structs and Classes
• Separation of Concerns (Mapped Model, Mapping, Storage)
• Type safe JSON
• How To Map
  • Nested Mappings
  • Binding and Collections
  • Mapping Payload
  • Custom Transformations
  • Different Mappings for Same Model
• Persistance Adapter
• Realm
• Supports Optional Types and Collections.

Requirements

iOS 10.0+ Swift 5.0+

v 0.12.0 for iOS 8 see swift-3 tag (v 0.6.0..<0.7.0) for Swift 3 see swift-4.0 tag for Swift 4.0 see swift-4.2 tag for Swift 4.2

Installation

CocoaPods

platform :ios, '10.0'
use_frameworks!

pod 'Crust'

Swift Package Manager (SPM)

dependencies: [
.package(url: "https://github.com/rexmas/Crust.git", .upToNextMinor(from: "0.13.0"))
]

Structs and Classes

Can map to/from classes or structs

class Company {
    var employees = Array<Employee>()
    var uuid: String = ""
    var name: String = ""
    var foundingDate: NSDate = NSDate()
    var founder: Employee?
    var pendingLawsuits: Int = 0
}

If you have no need for storage, which will generaly be the case for structs, use AnyMappable.

struct Person: AnyMappable {
    var bankAccounts: Array<Int> = [ 1234, 5678 ]
    var attitude: String = "awesome"
    var hairColor: HairColor = .Unknown
    var ownsCat: Bool? = nil
}

Separation of Concerns

By design Crust is built with separation of concerns in mind. It makes no assumptions about how many ways a user would like to map to and from JSON and how many various ways the user would like to store their models.

Crust has 2 basic protocols:

• Mapping - How to map JSON to and from a particular model - (model is set by the associatedtype MappedObject if mapping to an sequence of objects set associatedtype SequenceKind). - May include primary key(s) and nested mapping(s).
• PersistanceAdapter - How to store and retrieve model objects used for mapping from a backing store (e.g. Core Data, Realm, etc.).

And 2 additional protocols when no storage PersistanceAdapter is required:

• AnyMappable - Inherited by the model (class or struct) to be mapped to and from JSON.
• AnyMapping - A Mapping that does not require an PersistanceAdapter.

There are no limitations on the number of various Mappings and PersistanceAdapters one may create per model for different use cases.

JSONValue for type safe JSON

Crust relies on JSONValue for it’s JSON encoding and decoding mechanism. It offers many benefits including type safety, subscripting, and extensibility through protocols.

How To Map

1. Create a set of MappingKeys that define the key paths from the JSON payload to your model.

   enum EmployeeKey: MappingKey {
       case uuid
       case name
       case employer(Set<CompanyKey>)
   
       var keyPath: String {
           switch self {
           case .employer(_):          return "company"
           case .uuid:                 return "data.uuid"  // This means our JSON has a 'data' payload we're elevating.
           case .name:                 return "data.name"
           }
       }
   
       // You can specifically specify what keys you'd like to map from in the `keyedBy` argument of the mapper. This function retrieves the nested keys.
       func nestedMappingKeys<Key: MappingKey>() -> AnyKeyCollection<Key>? {
           switch self {
           case .employer(let companyKeys):
               return companyKeys.anyKeyCollection()
           default:
               return nil
           }
       }
   }
   
   enum CompanyKey: MappingKey {
       case uuid
       case name
       case employees(Set<EmployeeKey>)
       case founder(Set<EmployeeKey>)
       case foundingDate
       case pendingLawsuits
   
       var keyPath: String {
           switch self {
           case .uuid:                 "uuid"
           case .name:                 "name"
           case .employees(_):         "employees"
           case .founder(_):           "founder"
           case .foundingDate:         "data.founding_date"
           case .pendingLawsuits:      "data.lawsuits_pending"
           }
       }
   
       func nestedMappingKeys<Key: MappingKey>() -> AnyKeyCollection<Key>? {
           switch self {
           case .employees(let employeeKeys):
               return employeeKeys.anyKeyCollection()
           case .founder(let employeeKeys):
               return employeeKeys.anyKeyCollection()
           default:
               return nil
           }
       }
   }

2. Create your mappings for your model using Mapping if with storage or AnyMapping if without storage.

   With storage (assume CoreDataAdapter conforms to PersistanceAdapter)

   class EmployeeMapping: Mapping {
   
       var adapter: CoreDataAdapter
       var primaryKeys: [Mapping.PrimaryKeyDescriptor]? {
           // property == attribute on the model, keyPath == keypath in the JSON blob, transform == tranform to apply to data from JSON blob.
           return [ (property: "uuid", keyPath: EmployeeKey.uuid.keyPath, transform: nil) ]
       }
   
       required init(adapter: CoreDataAdapter) {
           self.adapter = adapter
       }
   
       func mapping(inout toMap: inout Employee, payload: MappingPayload<EmployeeKey>) throws {
           // Company must be transformed into something Core Data can use in this case.
           let companyMapping = CompanyTransformableMapping()
   
           // No need to map the primary key here.
           toMap.employer              <- (.mapping(.employer([]), companyMapping), payload)
           toMap.name                  <- (.name, payload)
       }
   }

   Without storage

   class CompanyMapping: AnyMapping {
       // associatedtype MappedObject = Company is inferred by `toMap`
   
       func mapping(inout toMap: inout Company, payload: MappingPayload<CompanyKey>) throws {
           let employeeMapping = EmployeeMapping(adapter: CoreDataAdapter())
   
           toMap.employees             <- (.mapping(.employees([]), employeeMapping), payload)
           toMap.founder               <- (.mapping(.founder([]), employeeMapping), payload)
           toMap.uuid                  <- (.uuid, payload)
           toMap.name                  <- (.name, payload)
           toMap.foundingDate          <- (.foundingDate, payload)
           toMap.pendingLawsuits       <- (.pendingLawsuits, payload)
       }
   }

3. Create your Crust Mapper.

   let mapper = Mapper()

4. Use the mapper to convert to and from JSONValue objects

   let json = try! JSONValue(object: [
               "uuid" : "uuid123",
               "name" : "name",
               "employees" : [
                   [ "data" : [ "name" : "Fred", "uuid" : "ABC123" ] ],
                   [ "data" : [ "name" : "Wilma", "uuid" : "XYZ098" ] ]
               ]
               "founder" : NSNull(),
               "data" : [
                   "lawsuits_pending" : 5
               ],
               // Works with '.' keypaths too.
               "data.founding_date" : NSDate().toISOString(),
           ]
   )
   
   // Just map 'uuid', 'name', 'employees.name', 'employees.uuid'
   let company: Company = try! mapper.map(from: json, using: CompanyMapping(), keyedBy: [.uuid, .name, .employees([.name, .uuid])])
   
   // Or if json is an array and you'd like to map everything.
   let company: [Company] = try! mapper.map(from: json, using: CompanyMapping(), keyedBy: AllKeys())

NOTE: JSONValue can be converted back to an AnyObject variation of json via json.values() and to NSData via try! json.encode().

Nested Mappings

Crust supports nested mappings for nested models E.g. from above

func mapping(inout toMap: Company, payload: MappingPayload<CompanyKey>) throws {
    let employeeMapping = EmployeeMapping(adapter: CoreDataAdapter())

    toMap.employees <- (Binding.mapping(.employees([]), employeeMapping), payload)
}

Binding and Collections

Binding provides specialized directives when mapping collections. Use the .collectionMapping case to inform the mapper of these directives. They include

• replace and/or delete objects
• append objects to the collection
• unique objects in collection (merge duplicates)
  • The latest mapped properties overwrite the existing object’s properties during uniquing. Properties not mapped remain unchanged.
  • Uniquing works automatically if the Elements of the collection being mapped follow Equatable.
  • If the Elements do not follow Equatable then uniquing is ignored unless UniquingFunctions are explicitly provided and the mapping function map(toCollection field:, using binding:, uniquing:) is used.
• Accept “null” values to map from the collection.

This table provides some examples of how “null” json values are mapped depending on the type of Collection being mapped to and given the value of nullable and whether values or “null” are present in the JSON payload.

append / replace	nullable	vals / null	Array	Array?	RLMArray
append	yes or no	vals	append	append	append
append	yes	null	no-op	no-op	no-op
replace	yes or no	vals	replace	replace	replace
replace	yes	null	removeAll	assign null	removeAll
append or replace	no	null	error	error	error

By default using .mapping will (insert: .replace(delete: nil), unique: true, nullable: true).

public enum CollectionInsertionMethod<Container: Sequence> {
    case append
    case replace(delete: ((_ orphansToDelete: Container) -> Container)?)
}

public typealias CollectionUpdatePolicy<Container: Sequence> =
    (insert: CollectionInsertionMethod<Container>, unique: Bool, nullable: Bool)

public enum Binding<M: Mapping>: Keypath {
    case mapping(Keypath, M)
    case collectionMapping(Keypath, M, CollectionUpdatePolicy<M.SequenceKind>)
}

Usage:

let employeeMapping = EmployeeMapping(adapter: CoreDataAdapter())
let binding = Binding.collectionMapping("", employeeMapping, (.replace(delete: nil), true, true))
toMap.employees <- (binding, payload)

Look in ./Mapper/MappingProtocols.swift for more.

Mapping Payload

Every mapping passes through a Payload: MappingPayload<T> which must be included during the mapping. The payload includes error information that is propagated back from the mapping to the caller and contextual information about the json and object being mapped to/from.

To include the payload during mapping include it as a tuple.

func mapping(inout toMap: Company, payload: MappingPayload<CompanyKey>) throws {
   toMap.uuid <- (.uuid, payload)
   toMap.name <- (.name, payload)
}

Custom Transformations

To create a simple custom transformation (such as to basic value types) implement the Transform protocol

public protocol Transform: AnyMapping {
    func fromJSON(_ json: JSONValue) throws -> MappedObject
    func toJSON(_ obj: MappedObject) -> JSONValue
}

and use it like any other Mapping.

Different Mappings for Same Model

Multiple Mappings are allowed for the same model.

class CompanyMapping: AnyMapping {
    func mapping(inout toMap: Company, payload: MappingPayload<CompanyKey>) throws {
        toMap.uuid <- (.uuid, payload)
        toMap.name <- (.name, payload)
    }
}

class CompanyMappingWithNameUUIDReversed: AnyMapping {
    func mapping(inout toMap: Company, payload: MappingPayload<CompanyKey>) throws {
        toMap.uuid <- (.name, payload)
        toMap.name <- (.uuid, payload)
    }
}

Just use two different mappings.

let mapper = Mapper()
let company1 = try! mapper.map(from: json, using: CompanyMapping(), keyedBy: AllKeys())
let company2 = try! mapper.map(from: json, using: CompanyMappingWithNameUUIDReversed(), keyedBy: AllKeys())

Persistance Adapter

Follow the PersistanceAdapter protocol to store data into Core Data, Realm, etc.

The object conforming to PersistanceAdapter must include two associatedtypes:

• BaseType - the top level class for this storage systems model objects.
  • Core Data this would be NSManagedObject.
  • Realm this would be RLMObject.
  • RealmSwift this would be Object.
• ResultsType: Collection - Used for object lookups. Should be set to a collection of BaseTypes.

The Mapping must then set it’s associatedtype AdapterKind = <Your Adapter> to use it during mapping.

Realm

There are tests included in ./RealmCrustTests that include examples of how to use Crust with realm-cocoa (Obj-C).

If you wish to use Crust with RealmSwift check out this (slightly outdated) repo for examples. https://github.com/rexmas/RealmCrust

Contributing

Pull requests are welcome!

• Open an issue if you run into any problems.
• Fork the project and submit a pull request to contribute. Please include tests for new code.
• Keep Linux tests up-to-date swift test --generate-linuxmain

License

The MIT License (MIT)

Copyright (c) 2015-2018 Rex

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.