RLMObject with array of strings

[Bruno-Furtado]

I have the following JSON and I need to convert it to object:

{
"title" : "Title",
"description" : "Description",
"tags" : ["First", "Second"]
}

I tried using the following class to serialize:

@interface Object : RLMObject
@property NSString *title;
@property NSString *description;
@property RLMArray<Tag> *tags;
@end

@interface Tag : RLMObject
@property NSString *value;
@end
RLM_ARRAY_TYPE(TGTag)

The following error message appears:

Terminating app due to uncaught exception 'RLMException', reason: 'Invalid value 'nil' for property 'value''

How could I serialize an array of pure strings?
Thanks and sorry for the silly question but have not found anything about it.

[GreatApe]

Hello Bruno-Fortado, thank you for trying Realm! It looks like you are trying to set a string property to nil, which is not possible at the moment. Could you share the code that produces the error?

(Looking at your model, is this exactly what it looks like? It looks like it shouldn't work, because the Tag interface should come before that for Object, and the RLM_ARRAY_TYPE macro has TGTag as argument.)

[Bruno-Furtado]

@GreatApe, sorry.
Exemplified in the wrong way.

Is another example:

JSON

{
"title" : "Title",
"rating" : 90,
"tags" : ["Tag1", "Tag2"]
}

NSDictionary

{
    rating = 90;
    tags =     (
        "Tag1",
        "Tag2"
    );
    title = "Title";
}

Models

#import "RLMObject.h"
#import "Tag.h"

@interface Recipe : RLMObject
@property NSString *title;
@property float rating;
@property RLMArray<Tag> *tags;
@end

#import "RLMObject.h"

@interface Tag : RLMObject
@property NSString *value;
@end
RLM_ARRAY_TYPE(Tag)

NSDictionary to RLMObject

AFHTTPRequestOperationManager *operationManager = [AFHTTPRequestOperationManager instance];
[operationManager GET:path parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
     // responseObject is NSDictionary
     Recipe *recipe = [[Recipe alloc] initWithObject:responseObject];        
} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
     completion(nil);
}];

Error

The error occurs when the object starts from the dictionary:

2014-10-16 08:41:50.445 App[77768:8853055] *** Terminating app due to uncaught exception 'RLMException', reason: 'Invalid value 'nil' for property 'value''

[GreatApe]

OK, thank you for clarifying. The issue is most likely that you are setting the tags property to the value @[@"tag1", @"tag2"] which is an NSArray, and not an RLMArray with object type Tag. You would need to manually parse it. One way would be to initWithObject with a dictionary where the tags property is an empty NSArray, and then manually populate that array with Tag objects.

[Bruno-Furtado]

@GreatApe,
Thank you so much!

Just a doubt, this array will be saved to the database normally?

[GreatApe]

Well, it depends on what you mean by 'normally', but probably the answer is yes!

Also, another way to do it would be to supply an NSArray of Tag objects, that would also work. So you would first create the Tag objects using the strings in that array, then put the Tag:s in an array and replace the string array in the dictionary with that. Then you can use initWithObject.

The thing is that if you give it an array of NSStrings when it expects an array of Tag:s is that it will not create those Tag:s from the strings. It is not that automatic. In this case it is pretty straightforward since Tag:s only have one property, which is an NSString, but generally speaking the RLMObject subclass that is contained in the array property could be arbitrarily complex.

This project would probably be useful for you if you want to parse anything more complex:
https://github.com/matthewcheok/Realm-JSON

[alazier]

@GreatApe is incorrect here. You can pass in an array of object literals which represent Tag objects and they will be created automatically. For example:

Recipe *recipe = [[Recipe alloc] initWithObject:@[@"title", @2, @[@[@"tag1"], @[@"tag2"]]]];

would create the recipe and its two tag automatically. The key is that each tag (and any other object) is represented by an array (or dictionary) of all its properties. Even in the case of Tag where there is one property it needs to be an array and not just the string which is the value of the sole property.

[GreatApe]

Sorry about that. In other words initWithObject is recursive but since it requires you to put the properties of a nested object in an array the dictionary you have will still need to be parsed, but at least you will not have to create the nested objects manually.

[ipeisong]

doesn't realm support sth like RLMArray ?

[GreatApe]

Sure, realm supports RLMArray, but an RLMArray can only contain instances of (subclasses of) RLMObjects, so you can't make an RLMArray of strings directly. In this case there was an RLMArray of Tag objects, where each Tag object had a single property, an NSString. So in order to init a Tag object you would have to do this:

Tag *aNewTagObject = [[Tag alloc] initWithObject:@["someTag"]];

or this:

Tag *aNewTagObject = [[Tag alloc] initWithObject:@{@"value" : "someTag"}];

So even if an RLMObject subclass only has one property, you have to put that property in an array or dictionary when you initialise it. Consequently, if you want to initialise an instance of the Recipe class, which contains a property that was an array of Tag objects, you have to put the value of each tag property in an array or dictionary, like in Ari's example:

{
    "title" : "Title",
    "description" : "Description",
    "tags" : [["First"], ["Second"]]
}

which is equivalent to:

{
    "title" : "Title",
    "description" : "Description",
    "tags" : [aTagInstanceWithValuePropertyEqualToFirst, aTagInstanceWithValuePropertyEqualToSecond]
}

but the dictionary that Bruno used had the tag strings directly in the tags array like this:

{
    "title" : "Title",
    "description" : "Description",
    "tags" : ["First", "Second"]
}

and then when initWithObject reaches the tags property it expects an array of Tag instances (or something that a recursive call to initWithObject can turn into that) and instead just finds an array of strings.

[ipeisong]

if a RLMObject has only one property, the initWithObject will find it even without having a default property name? In this case the property name is 'value', but if I name it as 'stringValue' it will work exactly the same, right?

[GreatApe]

Yes, and that actually works even if there are multiple properties, but then you need to make sure they are in the correct order. That is why in Ari's example he could initialise the Recipe object simply like this:

@[@"title", @2, @[@[@"tag1"], @[@"tag2"]]]

instead of this:

@{@"title" : @"title", @"rating" : @2, @"tags : "@[@[@"tag1"], @[@"tag2"]]}

which would also work.