Core Data Query Interface (CDQI) is a type-safe, fluent, intuitive library for working with Core Data in Swift. CDQI tremendously reduces the amount of code needed to do Core Data, and dramatically improves readability by allowing method chaining and by eliminating magic strings. CDQI is a bit like jQuery or LINQ, but for Core Data.
NOTE: The cdqi tool used to generate attribute proxies is deprecated. Bug fixes and changes in Swift make it very simple to hand-code attribute proxies, so the cdqi tool is no longer necessary.
Features
- Fluent interface, i.e., chainable methods
- Large number of useful overloads
- Type-safety in filter comparisons.
- Filtering, sorting, grouping, aggregate expressions, limits, etc.
- Optionally eliminates the use of magic strings so common in Core Data
- Query reuse, i.e., no side-effects from chaining
- Support for iOS 9+, macOS 10.11+, tvOS 9+, and watchOS 2+.
- Swift 5
Overview
In essence, CDQI is a tool that allows the creation (and execution) of fetch requests using a fluent syntax. In most cases, this can reduce many lines of code to a single (but still highly readable) line.
let swiftDevelopers = managedObjectContext.from(Developer.self).
filter(any(Developer.e.languages.name == "Swift"))
orderDesc(by: Developer.e.lastName)
.limit(5)
.all()
Integration
Carthage
In your Cartfile, add the following line:
github "prosumma/CoreDataQueryInterface" ~> 7.0
CocoaPods
Add the following to your Podfile. If it isn't already present, you will have to add use_frameworks! as well.
pod 'CoreDataQueryInterface', '~> 7.0'
Attribute And Model Proxies
CDQI works through the use of attribute and model proxies. In CDQI, a proxy is a type that stands in for a Core Data model or attribute. There are built-in proxies for all the Core Data attribute types, e.g., Int32Attribute, StringAttribute and so on. For your own Core Data models, you will need to create your own proxies, which is very simple to do. Imagine we have two Core Data models, Employee and Department. There is a many-to-one relationship in Core Data between these models. To keep things simple, each has a simple name attribute of type String:
class Employee: NSManagedObjectModel {
@NSManaged var name: String
@NSManaged var department: Department
}
class Department: NSManagedObjectModel {
@NSManaged var name: String
@NSManaged var employees: Set<Employee>
}
The proxy classes for these should look like this:
class EmployeeAttribute: EntityAttribute, Subqueryable {
public private(set) lazy var name = StringAttribute(key: "name", parent: self)
public private(set) lazy var department = DepartmentAttribute(key: "department", parent: self)
}
extension Employee: Entity {
public typealias CDQIEntityAttribute = EmployeeAttribute
}
class DepartmentAttribute: EntityAttribute, Subqueryable {
public private(set) lazy var name = StringAttribute(key: "name", parent: self)
public private(set) lazy var employees: EmployeeAttribute(key: "employees", parent: self)
}
extension Department: Entity {
public typealias CDQIEntityAttribute = DepartmentAttribute
}
Once this is done, CDQI can do its magic. Read on.
Starting a Query
A CDQI query is a chain of methods that build an NSFetchRequest. Almost all of the NSFetchRequest's functionality is supported, such as choosing the result type, limiting the number of records fetched, filtering, sorting, etc.
A query is started by creating an instance of Query, which takes two generic type parameters. The first one tells us which NSManagedObject subclass is the target of our query. The second tells us what the result of the query should be: Either the same NSManagedObject subclass or an NSDictionary.
let developerQuery = Query<Developer, Developer>()
let developerDictionaryQuery = Query<Developer, NSDictionary>()
Most Query instances are of the form Query<M, M> where M is an NSManagedObject which implements the Entity protocol. A perhaps better way to start a query is…
let developerQuery = Developer.cdqiQuery
Queries started with Query<Developer, Developer> or Developer.cdqiQuery have no implicit NSManagedObjectContext, so one must be passed when executing a query.
try Developer.cdqiQuery.order(by: Developer.e.lastName).all(managedObjectContext: moc)
try Developer.cdqiQuery,order(by: Developer.e.lastName).context(moc).all()
This pattern is so common that a convenience method exists on NSManagedObjectContext.
try moc.from(Developer.self).order(by: Developer.e.lastName).all()
Filtering
Filtering in Core Data requires an NSPredicate. CDQI has overloads of many of the built-in operators. These overloads generate Core Data friendly NSPredicates instead of Bools. They are carefully designed so as not to conflict with the ordinary operators.
| Swift | NSPredicate |
|---|---|
Developer.e.lastName == "Li" |
"lastName == 'Li'" |
Person.e.age >= 18 |
"age >= 18" |
21...55 ~= Person.e.age |
"age BETWEEN 21 AND 55" |
Person.e.firstName == "Friedrich" && Person.e.lastName == "Hayek" |
"firstName == 'Friedrich' AND lastName == 'Hayek'" |
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