Merge pull request #745 from ParsePlatform/nlutsenko.generics.relation

Add generics support to PFRelation.

Author: nlutsenko

Parse/PFRelation.h

@@ -18,7 +18,7 @@ NS_ASSUME_NONNULL_BEGIN
  The `PFRelation` class that is used to access all of the children of a many-to-many relationship.
  Each instance of `PFRelation` is associated with a particular parent object and key.
  */
-@interface PFRelation : NSObject
+@interface PFRelation<ObjectType : PFObject *> : NSObject
 
 /**
  The name of the class of the target child objects.
@@ -32,7 +32,7 @@ NS_ASSUME_NONNULL_BEGIN
 /**
  Returns a `PFQuery` object that can be used to get objects in this relation.
  */
-- (PFQuery *)query;
+- (PFQuery<ObjectType> *)query;
 
 ///--------------------------------------
 #pragma mark - Modifying Relations
@@ -43,14 +43,14 @@ NS_ASSUME_NONNULL_BEGIN
 
  @param object A `PFObject` object to add relation to.
  */
-- (void)addObject:(PFObject *)object;
+- (void)addObject:(ObjectType)object;
 
 /**
  Removes a relation to the passed in object.
 
  @param object A `PFObject` object to add relation to.
  */
-- (void)removeObject:(PFObject *)object;
+- (void)removeObject:(ObjectType)object;
 
 @end
 

Parse/PFRole.h

@@ -11,9 +11,12 @@
 
 #import <Parse/PFObject.h>
 #import <Parse/PFSubclassing.h>
+#import <Parse/PFUser.h>
 
 NS_ASSUME_NONNULL_BEGIN
 
+@class PFRelation<ObjectType : PFObject *>;
+
 /**
  The `PFRole` class represents a Role on the Parse server.
  `PFRoles` represent groupings of `PFUser` objects for the purposes of granting permissions
@@ -83,7 +86,7 @@ NS_ASSUME_NONNULL_BEGIN
  (e.g. read or write access through ACLs). You can add or remove users from
  the role through this relation.
  */
-@property (nonatomic, strong, readonly) PFRelation *users;
+@property (nonatomic, strong, readonly) PFRelation<PFUser *> *users;
 
 /**
  Gets the `PFRelation` for the `PFRole` objects that are direct children of this role.
@@ -92,7 +95,7 @@ NS_ASSUME_NONNULL_BEGIN
  (e.g. read or write access through ACLs). You can add or remove child roles
  from this role through this relation.
  */
-@property (nonatomic, strong, readonly) PFRelation *roles;
+@property (nonatomic, strong, readonly) PFRelation<PFRole *> *roles;
 
 @end
 

Parse/PFRole.m

@@ -51,11 +51,11 @@ + (instancetype)roleWithName:(NSString *)name acl:(PFACL *)acl {
 @dynamic name;
 
 // Dynamic synthesizers would use objectForKey, not relationForKey
-- (PFRelation *)roles {
+- (PFRelation<PFRole *> *)roles {
     return [self relationForKey:@keypath(PFRole, roles)];
 }
 
-- (PFRelation *)users {
+- (PFRelation<PFUser *> *)users {
     return [self relationForKey:@keypath(PFRole, users)];
 }