One_To_Many about sugar HOT 33 OPEN

Here’s an example:

Say you have two classes Author and Book. An Author can have many books.
In this case, the Book class would contain the Author object. like this:

class Book{
    String name;
    Author author;
}

class Author{
    String name;

    public List<Book> getBooks(){
        return Book.find(Book.class, "author = ?", new String{author.getId()})
    }
}

You can achieve the one to many relationship like this.

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@satyan Thanks, your example helped me to understand how to implement oneToMany relationships ! I suggest you to maybe add this on your doc as it is not so clear how to implement it, I struggled a bit before I found this issue !

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Many to many is slightly tricky.

You could create a LinkerClass similar to the link table in database, and use that to link the two objects.

eg:

Book
Author
AuthorBooks

where AuthorBooks would be

class AuthorBooks{
    Author author;
    Book book;
}

you can fetch in a similar style then:

List<AuthorBooks> authorBooks = AuthorBooks.find(AuthorBooks.class, “author = ?”, author.getId());

This would have the list of books.

It’s a round about approach.. but so far there’s no direct support for many to many relationship.

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I don't understand the example - I'm using 1.4, but the code won't compile.

class Book{
    String name;
    Author author;
}

class Author{
    String name;

    public List<Book> getBooks(){
        return Book.find(Book.class, "author = ?", new String{author.getId()})
    }
}

The "author.getId()" always says "cannot resolve symbol". This example seems very incomplete - neither class extends SugarRecord, and author and getId() are not visible symbols within the Author class. Am I missing something here?

Also, if I switch the anonymous String to an anonymous string array

new String[]{author.getId()})

That returns a long, not a string. Syntax errors abound.

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@MisterSpicy, please try this:

class Book extends SugarRecord<Book> {
    String name;
    Author author;
}

class Author extends SugarRecord<Author> {
    String name;

    public List<Book> getBooks(){
        return Book.find(Book.class, "author = ?", String.valueOf(this.getId()))
    }
}

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I never would have thought that I needed to check to see if a highly regarded ORM supported one-to-many relationships. This is absolutely crucial. Is there ever going to be an update to support this?

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I'm want understand how to make relationship one-to-many too. I try
private ArrayList images;
but this method doesn't work.
E/Sugar﹕ Class cannot be read from Sqlite3 database.

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ArrayList or other collections aren't supported yet. You could define your relationship like this example: http://satyan.github.io/sugar/creation.html#why

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I'm not sure based on the docs posted how to create a one to many relationship. Could you elaborate?

from sugar.

I've hit this roadblock also. Struggling with this one!

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Any chance of this being supported soon? Or does anyone recommend any other ORM for Android?

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Is this being worked on currently?

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Sugar does not handle many to many relationship for you currently. You'd have to manage the relationship yourself using an approach suggested above #60 (comment)

It's not worked upon currently. Would love to hear some suggestions on this..

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I'd definitely like to help if I can. Would you mind chatting a bit via email? I sent you one a few minutes ago before I stumbled upon this ticket.

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+1 on the suggestion of @OlivierRevial to add the example on the documentation!

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yes, +1 on adding that to the documentation! i was struggling with this for hours because i didnt know that Collections aren't supported

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What about one to many relationships? Are this being worked on?

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An book can have many Authors how to insert the values in this condition ?

class Book{
    String name;
    Author author;
 public List<Author> getAuthors{
        return Author.find(Book.class, "name = ?", new String{author.getName()})
    }

}

class Author{
    String name;
...

}

above code is correct ?

To-Many lists Relations?
One more thing how to insert the list of (array/Arraylist) values to One To Many relationship? (like mentioned in GreenDAO http://greendao-orm.com/documentation/relations/)

code from AddNoteActivity of Samples

Tag tag = new Tag(tagBox.getText().toString());
                save(tag);
                save(new Note(10 + (int) (10 * Math.random()), titleBox.getText().toString(), descBox.getText().toString(), tag));

How to save if there are list of many tags to the note?

List<Tag> taglist=new ArrayList<Tag>();
taglist.add(new Tag("Tagname")):
.
.
.

Tag tag = new Tag(taglist);

save(tag);

  save(new Note(10 + (int) (10 * Math.random()), titleBox.getText().toString(), descBox.getText().toString(), tag));

this Will work for inserting many tags to to a single note? or any other ways to achieve this?

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Ah just ran into this solution, but wanted to share what I ended up doing, maybe it helps someone out:

• @ignore the actual list structure
• Add a String "listJson" or the likes that keeps a json representation of the list
• Make sure that listJson is in sync before calling save on the object
• in you getList() method restore the list structure from the listJson String if the structure is empty/null

Not the most efficient/clean way but works for me for now (using small lists). Hoping to see proper list support soon though!

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Thanks Cuberob for the Info, I finally did it in the same way by storing the string in json format! but json/gson parsing while retrieving inserting will effect performance! GeenDAO have mentioned some solutions for this.. Need try that Ref: #195

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This is definitely much needed functionality. Is there a way to pass values to the constructor for sugar orm? I know it needs the default constructor. If possible then we can build up the many - many lists by passing the parent_id to the child_id class. So on querying the parent, in the constructor you do the find all by parent_id and build that object in the parent.

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This is a critical feature and it will go into 1.4.0.

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Is this feature present in 1.4 beta release ?

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@rdenadai Hey, thanks for that, I was pretty tired and a little frustrated. I also found the whole set of examples in the project, which implements things like you have. Hopefully the docs get updated soon for 1.4!

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sorry,who can give me one full example about one-to-many?I'm always not successThanks

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Documentation did not help guys. I tried more than 1 time to implement simple Relation One to Many without succes. Android crash every time saying: android.database.sqlite.SQLiteException: no such column: travelSugar (code 1): , while compiling: SELECT * FROM PLACE_SUGAR WHERE travelSugar = ? where travelSugar is like "author" in @MisterSpicy above comment

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@multivoltage In Sugar your field(travelSugar) will be represented as 'travel_sugar' in the database. So try like this YourClass.find(YourClass.class,"travel_sugar = ?", "somthing");

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I don't understand how the example is supposed to work when you can't store objects as parameters in sugar, I mean the one with the Book and the Author. I get an error "no such column: author (code 1)" which is exactly what I expected when I saw the example, am I missing something?

If I could store objects as parameters in the database I wouldn't need to use a one to many solution.

EDIT: I found my problem, I had a table with something like this "nameTable", but sugarORM automatically changes those kinds of names to "name_table", so I had to search for it that way.

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@satyan So we will have a direct support for many-to-many relationship in 2.0.0 for sure?

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Hello.
I am a little confused.

class Book extends SugarRecord<Book> {
    String name;
    Author author;
}

class Author extends SugarRecord<Author> {
    String name;

    public List<Book> getBooks(){
        return Book.find(Book.class, "author = ?", String.valueOf(this.getId()))
    }
}

This code is really needed?

public List<Book> getBooks(){
        return Book.find(Book.class, "author = ?", String.valueOf(this.getId()))
    }

Thank you for helping me.

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public String venueId;
public String venueName;
public String venueType;
public List < String > profileImages = new ArrayList < String > ();

this is my response model keys.. what should i do so that i can store that profileImages array in my database using SugarORM v1.5?
if any one can help please reply me , thank you

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I'm having save issue with one to many relationship.

The example here http://satyan.github.io/sugar/creation.html#why is too vague and it also seems that @OneToMany annotation is removed in 1.5 release.

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If someone can help. I have a similar kind of issue.. https://stackoverflow.com/questions/45389403/sugarorm-not-saving-object-inside-arraylist

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