When you design your Core Data data model, you can choose between a whole bunch of data types for your attributes. In your managed object model, many of these data types (namely, Integer 16, Integer 32, Integer 64, Double, Float, and Bool) are modeled with a property of type NSNumber *.

What if, for some reason, you need to determine the underlying data type of a Core Data attribute in your code? Turns out this is quite easy using Core Data’s introspection APIs.

NSEntityDescription

As you probably know, each entity in your Core Data model is represented by an instance of NSEntityDescription. So suppose you have an entity named “Person”:

NSEntityDescription *personEntity = [NSEntityDescription entityForName:@"Person" inManagedObjectContext:self.managedObjectContext];

NSPropertyDescription and NSAttributeDescription

Following this pattern, each property an entity has is represented by an instance of a subclass of NSPropertyDescription, depending on the kind of property we are dealing with: attribute (represented by NSAttributeDescription), relationship (NSRelationshipDescription), or fetched property (NSFetchedPropertyDescription).

To iterate over all properties of your entity, do this:

for (NSPropertyDescription *property in eventEntity) {
    ...
}

If you are just interested in the entity’s attributes, the -attributesByName method returns a dictionary you can either iterate over or ask for a specific attribute. The NSPropertyDescription and NSAttributeDescription classes then offer methods to inspect the attribute’s properties, e.g. the -attributeType:

NSDictionary *attributes = [eventEntity attributesByName];
NSAttributeDescription *ageAttribute = [attributes objectForKey:@"age"];
if ([ageAttribute attributeType == NSInteger32AttributeType]) {
    // We have a 32-bit Integer
    ...
}

NSAttributeType

Valid values for NSAttributeType are listed in the NSAttributeDescription.h header:

// types explicitly distinguish between bit sizes to ensure data store
// independence of the underlying operating system
enum {
    NSUndefinedAttributeType = 0,
    NSInteger16AttributeType = 100,
    NSInteger32AttributeType = 200,
    NSInteger64AttributeType = 300,
    NSDecimalAttributeType = 400,
    NSDoubleAttributeType = 500,
    NSFloatAttributeType = 600,
    NSStringAttributeType = 700,
    NSBooleanAttributeType = 800,
    NSDateAttributeType = 900,
    NSBinaryDataAttributeType = 1000
    // If your attribute is of NSTransformableAttributeType, the attributeValueClassName
    // must be set or attribute value class must implement NSCopying.
    , NSTransformableAttributeType = 1800
    , NSObjectIDAttributeType = 2000
};

typedef NSUInteger NSAttributeType;