Develop Reference

Is it possible to hide some fields from our model?

I decided to use Room for caching data and now because of the situation of the library that I developed, I need to hide some fields of my model and then give them to the client that use my library.
The model below had orderId and I added this because I need that but when I don't want to give this filled model with orderId. i know how to ignore fields in JSON. But how can i hide this one from my model and then give it to the client.
Do I make a mistake in using Room in the first place?
public class Participant {
#PrimaryKey
private long id;
#ColumnInfo(name = "order_id")
private long orderId;
private long threadId;
private String name;
private String firstName;
private String lastName;
For example :
i have a listener that is like the below
listener.add(participant);
i want to hide orderId first and then pass it to the listener.
Then in another class override this:
#Override
public void onAdd(Paticipant participant) {
super.onAdd(participant);
//here
}

One way to hide orderId from classes which use Participant, is to provide a getter for this variable and return null:
public Long getOrderId() {
return null;
}
We must change orderId to a Long in order for it to be set as null.
Additionally, you can override the toString() method to ignore orderId in any string representations of the class.

Use GSON library and create a new class for JSON model, without orderId:
class ParticipantJson {
final long id;
final long threadId;
final String name;
final String firstName;
final String lastName;
// Constructor
}
Then you can create JSON representation with:
ParticipantJson participant = new ParticipantJson(/* fields from Room model */);
Gson gson = new Gson();
String json = gson.toJson(participant);

USE A DIFFERENT MODEL FOR PRESENTATION!
Sorry for the caps but I cannot emphasize how important it is to use a different model for presentation.
Although you can hide fields from libraries like GSON or ROOM using keywords like transient or annotation like ignore you cannot hide a model attribute from class itself. Also remember that you cannot enforce a rule on a model that is not designed for the purpose.
TLDR; Create a new model and using a mapper map the Room model to this new presentation model.

Confuse on dealing with relations between objects using Android Room

When using the android data-persistent library Android Room ,how can I directly insert the Comment Object into the database including all the field value, and how can I query all the value out as a Comment Object?
As I know, I can not use the Comment Object as a Entity in Room directory, because of the field replyComment is also a Comment Object. And I can not query out a Comment Object even I define a POJO using the #Relations annotation either because of the one-to-one relations and one-to-many relations all included in the Comment Object.
Is there any other way except changing the Comment Model definition, such as using foreign key, making a effect on insert action and query action?
public class Comment {
public String content;
public String id;
public Comment replyComment;
public User user;
public List<ImageMedia> images;
}
public class User{
public String id;
public String name;
}
public class ImageMedia{
public String key;
public String url;
}

Is there any other way except changing the Comment Model definition
No. You would need to create a set of entities that model the database structure, where children have foreign key columns pointing back to their parents:
CommentEntity has a foreign key back to CommentEntity for the reply
CommentEntity has a foreign key back to UserEntity
ImageMediaEntity has a foreign key back to CommentEntity

Sugar ORM overwrites ID from feed

I'm writing an Android application that uses Sugar ORM for my data persistence. I have a case where I am getting an objectID from a web server, and this ID needs to be the same as my record's ID on the local database. That way my data record will be updated correctly when saved later on.
The issue I am having is that whenever I extend the SugarRecord class Sqlite is overwriting the ID I am setting in the object. For example, the ID in my feed is 2 but when inserted into the database the ID is changed to 1.
Is there anyways to prevent the auto incrementing that the database is doing with Sugar ORM?
Thanks!

In sugar ORM primary key with autoincrement property is set with id column by default.Try to update the schema version by entering some higher number in Manifest file and also rename the variable(id variable in POJO class)

I had the same problem that I solved by overwriting the ID setter in my model class like this :
public class MyClass extends SugarRecord {
#Unique
private Long id;
// default constructor for SugarRecord
public MyClass() {
}
#Override
public Long getId() {
return this.id;
}
#Override
public void setId(Long id) {
// Use "super" to overwrite
super.setId(id);
this.id = id;
}
}

Practical use of #Ignore in Realm?

I've been trying to add Realm in my Android app. Their docs are pretty well explained & easy to follow. But it fails to explain this one particular area. I'm unable to figure out the practical use for the #Ignore annotation. I know that fields under this annotation are not persisted.
Can someone please share a few use cases. Also I wanted to know the scope of such fields. I mean, if I set an #Ignore field to some value, would that value be available to the other classes in my app for that particular launch session. If yes, then how do we access it? If no (which I guess is the case), then why do we need such a field anyway?
I've searched here and on web but couldn't find the relevant information. If out of my ignorance, I've missed upon some resource, please guide me to it.
Thanks.

Accordingly to the official documentation (see https://realm.io/docs/java/latest/) #Ignore is useful in two cases:
When you use GSON integration and your JSON contains more data than you want to store, but you still would like to parse it, and use right after.
You can't create custom getters and setter in classes extending RealmObject, since they are going to be overridden. But in case you want to have some custom logic anyway, ignored fields can be used as a hack to do that, because Realm doesn't override their getter & setters. Example:
package io.realm.entities;
import io.realm.RealmObject;
import io.realm.annotations.Ignore;
public class StringOnly extends RealmObject {
private String name;
#Ignore
private String kingName;
// custom setter
public void setKingName(String kingName) { setName("King " + kingName); }
// custom getter
public String getKingName() { return getName(); }
// setter and getter for 'name'
}
Ignored fields are accessible only from the object they were set in (same as with regular objects in Java).
UPDATE: As the #The-null-Pointer- pointed out in the comments the second point is out of date. Realm now allows having custom getters and setters in Realm models.

Here's a couple of real-world use cases:
1 - Get user's fullname:
public class User extends RealmObject {
private String first;
private String last;
#Ignore
private String fullName;
public String getFullName() {
return getFirst() + " " + getLast();
}
Get JSON representation of object:
public class User extends RealmObject {
private String first;
private String last;
#Ignore
private JSONObject Json;
public JSONObject getJson() {
try {
JSONObject dict = new JSONObject();
dict.put("first", getFirst());
dict.put("last", getLast());
return dict;
} catch (JSONException e) {
// log the exception
}
return null;
}

I've found it useful to define field names for when I am querying. For example
User.java
public class User extends RealmObject {
#Index
public String name;
#Ignore
public static final String NAME = "name";
}
And then later on I can do something like:
realm.where(User.class).equalTo(User.NAME, "John").findFirst();
This way if the schema changes from say name to id I don't have to hunt down every occurrence of "name".

Please see the the official documentation about #Ignore annotation:
The annotation #Ignore implies that a field should not be persisted to disk. Ignored fields are useful if your input contains more fields than your model, and you don’t wish to have many special cases for handling these unused data fields.

How to make a field auto increment in ActiveAndroid ORM

How can I make an integer or long field to be auto-incremented using annotation.

As we can read in a documentation:
One important thing to note is that ActiveAndroid creates an id field
for your tables. This field is an auto-incrementing primary key.
Maybe accessing auto-generated primary key will be enough for you?
Moreover, if you would like to create custom primary key in you model, you can check solution mentioned in GitHub issue connected with ActiveAndroid, which looks like this:
#Table(name = "Items", id = "clientId")
public class Item extends Model {
#Column(name = "id")
private long id;
}
Then, id field is custom primary key, which will be auto-incremented.

In case of ActiveAndroid ORM you do not need to write id column in model, It will automatic generate auto incremented value and you can simply use it.
I am giving a sample model below-
#Table(name="Items")
public class Item extends Model{
#Column(name="name")
public String name;
}
Instead of
#Table(name="Items")
public class Item extends Model{
#Column(name="Id")
public long id;
#Column(name="name")
public String name;
}
If item is an object of Item then you can simply get id by using
item.getId();
So, the correct model is first one. For reference you can click here.