Alexandr Alexandr - 4 years ago 171
JSON Question

Using Realm with Gson

I have

json
with field
_id


String json = "{ _id : 1, name : 'Alex', role: 'admin' }"


In my Realm model I use
@SerializedName
attribute:

public class User extends RealmObject {

@SerializedName("_id")
@PrimaryKey
private int id;
private String name;
private String comment;

public int getId() {
return id;
}

public void setId(int id) {
this.id = id;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public String getComment() {
return comment;
}

public void setComment(String comment) {
this.comment = comment;
}

}


If try save the json:

realm.createOrUpdateObjectFromJson(User.class, json)


field
_id
can't parsed and in database created record with id = 0

In docs using
@SerializedName
attribute

Gson gson = new GsonBuilder()
.setExclusionStrategies(new ExclusionStrategy() {
@Override
public boolean shouldSkipField(FieldAttributes f) {
return f.getDeclaringClass().equals(RealmObject.class);
}

@Override
public boolean shouldSkipClass(Class<?> clazz) {
return false;
}
}).create();


User user = gson.fromJson(json, User.class);
realm.beginTransaction();
realm.copyToRealmOrUpdate(user);


In this case
json = "{ _id : 1, role: 'user' }"
just remove user
name
from database, because default value for String is null.

So, probably I incorrectly using the attribute. How to consider the attribute when dealing with the methods of conservation of json (
createOrUpdateObjectFromJson
, etc)?

Answer Source

You probably need a hybrid solution in order to make this work. The reason is that @SerializedName is a GSON annotation and not one that Realm knows about. So this means you have two choices as you already discovered:

1) Use GSON, which means the end result is an object with null as the default for name.

2) Use createOrUpdateObjectFromJson which means that _id will be ignored because Realm's JSON parser require a 1:1 mapping.

As neither solution will work correctly you can modify them in the following way:

1) With GSON, instead of doing copyToRealmOrUpdate you can manually search for the object and update the role:

realm.beginTransaction();
realm.where(User.class).equalTo("id", user.getId()).findFirst().setRole(user.getRole());
realm.commitTransaction();

2) Using just the pure JSON you can modify to match the expected format:

JSONObject obj = new JSONObject(json);
obj.put("id", obj.getString("_id"));
obj.remove("_id");

Realm has an issue tracking the request for custom mappings, but it has a low priority as that feature is usually better covered by frameworks such as GSON, Jacokson, etc. : https://github.com/realm/realm-java/issues/1470

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